Chapter 21: Anesthesia for Patients with Cardiovascular Disease

Cardiovascular diseases—particularly hypertensive, ischemic, congenital, and valvular heart disease—are among the medical illnesses most frequently encountered in anesthetic practice and are a major cause of perioperative morbidity and mortality. The neuroendocrine response to surgical stimulation and the circulatory effects of anesthetic agents, endotracheal intubation, positive-pressure ventilation, blood loss, fluid shifts, and alterations in body temperature impose additional burdens on an often already compromised cardiovascular system. Most anesthetic agents cause cardiac depression, vasodilation, or both. Even anesthetics that have no direct circulatory effects may cause apparent circulatory depression in severely compromised patients who are dependent on the enhanced sympathetic activity characteristic of heart failure or acute blood loss. Decreased sympathetic activity as a consequence of the anesthetized state can lead to acute circulatory collapse.

Anesthetic management of patients with cardiovascular disease requires a thorough knowledge of normal cardiac physiology, the circulatory effects of the various anesthetic agents, and the pathophysiology and treatment of these diseases. The same principles used in treating cardiovascular diseases in patients not undergoing surgery should be used perioperatively. In most instances, the choice of anesthetic agent is not terribly important; on the other hand, knowing how the agent is used, understanding the underlying pathophysiology, and understanding how the two interact are critical.

Patients with severe cardiovascular illnesses commonly undergo both cardiac and noncardiac surgery. The American College of Cardiology (ACC) has collaborated with the American Heart Association (AHA) in issuing numerous guidelines related to the management of patients with heart disease, and many of their recommendations are relevant to patients undergoing sedation or anesthesia. Because guidelines change as new evidence becomes available, readers are advised to review the AHA website for current evidence-based indications for the management of heart disease.

The prevalence of cardiovascular disease increases with advancing age. Moreover, the number of patients older than 65 years of age is expected to increase by 25% to 35% over the next two decades. Cardiovascular complications are estimated to account for 25% to 50% of deaths following noncardiac surgery. Perioperative myocardial infarction (MI), pulmonary edema, systolic and diastolic heart failure, arrhythmias, stroke, and thromboembolism are the most common diagnoses in patients with preexisting cardiovascular disease. The relatively high prevalence of cardiovascular disorders in surgical patients has given rise to attempts to define cardiac risk or the likelihood of intraoperative or postoperative fatal or life-threatening cardiac complications.

The ACC/AHA Task Force Report provides guidelines for perioperative cardiovascular evaluation. The guidelines state that the patient’s medical history is critical in determining the requirements for preoperative cardiac evaluation and that certain conditions (eg, unstable coronary syndromes and decompensated heart failure) warrant cardiology intervention prior to all but emergency procedures. The preoperative history should also address any past procedures, such as cardioverter defibrillator implants, coronary stents, and other interventions. Additionally, the patient’s ability to perform the tasks of daily living should be assessed as a guide to determine functional capacity. A patient with a history of cardiac disease and advanced age, but good exercise tolerance, will likely have a lower perioperative risk than a similar individual with dyspnea after minimal physical activity (Table 21–1).

The patient should be queried about other disease processes that frequently accompany heart disease. Cardiac patients often present with obstructive pulmonary disease, reduced kidney function, and diabetes mellitus.

A physical examination should be performed on all patients, and the heart and lungs should be auscultated. The physical examination is especially useful in patients with certain conditions. For example, if a harsh systolic murmur suggestive of aortic stenosis is detected in a candidate for elective surgery, additional ultrasound evaluation will likely be warranted, as aortic stenosis substantially increases the risks in patients undergoing noncardiac surgery.

The following conditions are associated with increased risk:

• Ischemic heart disease (history of MI, evidence on electrocardiogram [ECG], chest pain)

• Congestive heart failure (dyspnea, pulmonary edema)

• Cerebral vascular disease (stroke)

• High-risk surgery (vascular, thoracic)

• Diabetes mellitus

• Preoperative creatinine greater than 2 mg/dL

The ACC/AHA guidelines identify conditions that are a major cardiac risk and warrant intensive management prior to all but emergent surgery. These conditions include unstable coronary syndromes (recent MI, unstable angina), decompensated heart failure, significant arrhythmias, and severe valvular heart disease. The ACC/AHA guidelines identify an MI within 7 days, or one within 1 month with myocardium at risk for ischemia, as “active” cardiac conditions. On the other hand, evidence of past MI with no myocardium thought at ischemic risk is considered a low risk for perioperative infarction after noncardiac surgery. The ACC/AHA guidelines classify recommendations into four categories, as class I (benefit >>> risk), class IIa (benefit >> risk), class IIb (benefit ≥ risk), and class III (no benefit or harm). Additionally, they grade the strength of the evidence upon which the recommendations is based as A (multiple randomized trials), B (limited trials, nonrandomized studies), and C (consensus of experts, case studies).

Class I recommendations are as follows:

• Patients who have a need for emergency noncardiac surgery should proceed to the operating room with perioperative surveillance and postoperative risk factor management

• Patients with active cardiac conditions should be evaluated by a cardiologist and treated according to ACC/AHA guidelines

• Patients undergoing low-risk procedures should proceed to surgery

• Patients with poor exercise tolerance (<4 metabolic equivalents [METs]) and no known risk factors should proceed to surgery

The ACC/AHA guidelines use an algorithmic approach to discern risks of major adverse cardiac events (MACE; eg, perioperative death or myocardial infarction). Risks accrue secondary both to the nature of surgery and because of patient characteristics. The ACC/AHA suggest various risk calculators that are available online (eg, American College of Surgeons risk calculator, www.surgicalriskcalculator.com) to estimate patient risk of perioperative major adverse cardiac events (Figure 21–1).

The ACC/AHA guidelines also provide specific recommendations regarding various preexistent cardiac conditions (eg, heart failure, valvular heart disease, arrhythmias) likely to be encountered perioperatively. Recommendations regarding supplemental preoperative evaluation are presented in Table 21–2.

CORONARY ARTERY DISEASE

The ACC/AHA guidelines suggest that 60 days or more should elapse after an MI before noncardiac surgery in patients who were not treated with a coronary intervention. Moreover, an MI within 6 months of surgery is associated with increased perioperative mortality. Increased patient age and frailty are likewise associated with greater risk for acute coronary syndromes and stroke. Recently, studies have found a surprising number of asymptomatic patients with elevated levels of troponin after surgery. Such findings are indicative of myocardial injury despite there being no other evidence suggestive of MI. Nevertheless, these patients are at considerably increased risk. The specific management of these patients remains controversial.

HYPERTENSION

Patients with hypertension frequently present for elective surgical procedures. Some will have been effectively managed, but unfortunately, many others will not have been. Hypertension is a leading cause of death and disability in most Western societies and the most prevalent preoperative medical abnormality in surgical patients, with an overall prevalence of 20% to 25%. Long-standing uncontrolled hypertension accelerates atherosclerosis and hypertensive organ damage. Hypertension is a major risk factor for cardiac, cerebral, renal, and vascular disease. Complications of hypertension include MI, congestive heart failure, stroke, renal failure, peripheral occlusive disease, and aortic dissection. The presence of concentric left ventricular hypertrophy (LVH) in hypertensive patients may be an important predictor of cardiac mortality. However, systolic blood pressures below 180 mm Hg, and diastolic pressures below 110 mm Hg, have not been associated with increased perioperative risks. When patients present with systolic blood pressures greater than 180 mm Hg and diastolic pressures greater than 110 mm Hg, anesthesiologists face the dilemma of delaying surgery to allow optimization of oral antihypertensive therapy, but adding the risk of a surgical delay versus proceeding with surgery and achieving blood pressure control with rapidly acting intravenous agents. The incidence of adverse cardiac events in patients treated and operated upon may be similar to that in patients delayed to allow for better long-term blood pressure control. Of note, patients with preoperative hypertension are more likely than others to develop intraoperative hypotension.

Blood pressure measurements are affected by many variables, including posture, time of day, emotional state, recent activity, and drug intake, as well as the equipment and technique used. A diagnosis of hypertension cannot be made with one preoperative reading, but requires confirmation by a history of consistently elevated measurements. Although preoperative anxiety or pain may produce some degree of hypertension in normal patients, patients with a history of hypertension generally exhibit greater preoperative elevations in blood pressure.

Epidemiological studies demonstrate a direct and continuous correlation between both diastolic and systolic blood pressures and mortality rates. The definition of systemic hypertension is arbitrary: a consistently elevated diastolic blood pressure greater than 90 mm Hg or a systolic pressure greater than 140 mm Hg. A common classification scheme is listed in Table 21–3. Prehypertension is said to exist when the diastolic pressure is 80–89 mm Hg or the systolic pressure is 120–139 mm Hg. Whether patients with borderline hypertension are at some increased risk for cardiovascular complications remains unclear. Accelerated or severe hypertension is defined as a recent, sustained, and progressive increase in blood pressure, usually with diastolic blood pressures in excess of 110 to 119 mm Hg. Kidney dysfunction is often present in such patients. A hypertensive urgency reflects blood pressure elevation of >180/120 mm Hg without signs of organ injury (eg, hypertensive encephalopathy, heart failure). A hypertensive emergency is characterized by severe hypertension (>180/120 mm Hg) often associated with papilledema, encephalopathy, or other organ injury.

Pathophysiology

Hypertension can be either idiopathic (essential) or, less commonly, secondary to other medical conditions such as renal disease, renal artery stenosis, primary hyperaldosteronism, Cushing disease, acromegaly, pheochromocytoma, pregnancy, or estrogen therapy. Essential hypertension accounts for 80% to 95% of cases and may be associated with an abnormal baseline elevation of cardiac output, systemic vascular resistance (SVR), or both. An evolving pattern is commonly seen over the course of the disease, where cardiac output returns to (or remains) normal, but SVR becomes abnormally high. The chronic increase in cardiac afterload results in concentric left ventricular hypertrophy and altered diastolic function. Hypertension also alters cerebral autoregulation, such that normal cerebral blood flow is maintained in the face of high blood pressures; autoregulation limits may be in the range of mean blood pressures of 110 to 180 mm Hg.

The mechanisms responsible for the changes observed in hypertensive patients seem to involve vascular hypertrophy, hyperinsulinemia, abnormal increases in intracellular calcium, and increased intracellular sodium concentrations in vascular smooth muscle and renal tubular cells. Sympathetic nervous system overactivity and enhanced responses to sympathetic agonists are present in some patients. Hypertensive patients sometimes display an exaggerated response to vasopressors and vasodilators. Overactivity of the renin–angiotensin–aldosterone system seems to play an important role in patients with accelerated hypertension.

Long-Term Treatment

Effective drug therapy reduces the progression of hypertension and the incidence of stroke, congestive heart failure, coronary artery disease (CAD), and kidney damage. Effective treatment can also delay and sometimes reverse concomitant pathophysiological changes, such as left ventricular hypertrophy and altered cerebral autoregulation.

Some patients with mild hypertension require only single-drug therapy, which may consist of a thiazide diuretic, angiotensin-converting enzyme (ACE) inhibitor, angiotensin-receptor blocker (ARB), β-adrenergic blocker, or calcium channel blocker, although guidelines and outcome studies favor the first three options. Concomitant illnesses should guide drug selection. All patients with a prior MI should receive a β-adrenergic blocker and an ACE inhibitor (or ARB) to improve outcomes, irrespective of the presence of hypertension. In many patients, the “guideline-specified” agents will also be more than sufficient to control hypertension.

Patients with moderate to severe hypertension often require two or three drugs for control. The combination of a diuretic with a β-adrenergic blocker and an ACE inhibitor is often effective when single-drug therapy is not. As previously noted, ACE inhibitors (or ARBs) prolong survival in patients with congestive heart failure, left ventricular dysfunction, or a prior MI. Familiarity with the names, mechanisms of action, and side effects of commonly used antihypertensive agents is important for anesthesiologists (Table 21–4).

PREOPERATIVE MANAGEMENT

A recurring question in anesthetic practice is the degree of preoperative hypertension that is acceptable for patients scheduled for elective surgery. Except for optimally controlled patients, most hypertensive patients present to the operating room with some degree of hypertension. Although data suggest that even moderate preoperative hypertension (diastolic pressure >90–110 mm Hg) is not clearly statistically associated with postoperative complications, other data indicate that the untreated or poorly controlled hypertensive patient is more apt to experience intraoperative episodes of myocardial ischemia, arrhythmias, or hemodynamic instability. Careful intraoperative adjustments in anesthetic depth and use of vasoactive drugs should reduce the incidence of postoperative complications referable to poor preoperative control of hypertension.

Although patients should ideally undergo elective surgery only when rendered normotensive, accomplishing this over the short term is not always feasible or even desirable because hypertensive patients have altered cerebral autoregulation. Excessive reductions in blood pressure can compromise cerebral perfusion. Moreover, the decision to delay or to proceed with surgery should be individualized, based on the severity of the preoperative blood pressure elevation; the likelihood of coexisting myocardial ischemia, ventricular dysfunction, or cerebrovascular or renal complications; and the nature and urgency of the procedure. With rare exceptions, antihypertensive drug therapy should be continued up to the time of surgery. Some clinicians withhold ACE inhibitors and ARBs on the morning of surgery because of their association with an increased incidence of intraoperative hypotension; however, withholding these agents increases the risk of marked perioperative hypertension and the need for parenteral antihypertensive agents. It also requires the surgical team to remember to restart the medication after surgery. The decision to delay elective surgical procedures in patients with sustained preoperative diastolic blood pressures higher than 110 mm Hg should be made when the perceived benefits of delayed surgery exceed the risks. Unfortunately, there are few appropriate studies to guide the decision-making.

History

The preoperative history should address the severity and duration of the hypertension, the drug therapy currently prescribed, and the presence or absence of hypertensive complications. Symptoms of myocardial ischemia, ventricular failure, impaired cerebral perfusion, or peripheral vascular disease should be elicited, as well as the patient’s record of compliance with the drug regimen. The patient should be questioned regarding chest pain, exercise tolerance, shortness of breath (particularly at night), dependent edema, postural lightheadedness, syncope, episodic visual disturbances or episodic neurological symptoms, and claudication. Adverse effects of current antihypertensive drug therapy (Table 21–5) should also be identified.

Physical Examination & Laboratory Evaluation

Ophthalmoscopy is useful in hypertensive patients. Visible changes in the retinal vasculature usually parallel the severity and progression of arteriosclerosis and hypertensive damage in other organs. An S₄ cardiac gallop is common in patients with LVH. Other physical findings, such as pulmonary rales and an S₃ cardiac gallop, are late findings and indicate congestive heart failure. Blood pressure can be measured in both the supine and standing positions. Orthostatic changes may be due to volume depletion, excessive vasodilation, or sympatholytic drug therapy. Preoperative administration of a carbohydrate drink the night before and on the morning of surgery can promote hemodynamic stability after induction of anesthesia. Although asymptomatic carotid bruits are usually hemodynamically insignificant, they may be reflective of atherosclerotic vascular disease that may affect the coronary circulation. When a bruit is detected, further workup should be guided by the urgency of the scheduled surgery and the likelihood that further investigations, if diagnostic, would result in a change in therapy. Doppler studies of the carotid arteries can be used to define the extent of carotid disease.

The ECG is often normal, but in patients with a long history of hypertension, it may show evidence of ischemia, conduction abnormalities, an old infarction, or LVH or strain. A normal ECG does not exclude CAD or LVH. Similarly, a normal heart size on a chest radiograph does not exclude ventricular hypertrophy. Echocardiography is a sensitive test for LVH and can be used to evaluate ventricular systolic and diastolic functions in patients with symptoms of heart failure. Chest radiographs are rarely useful in an asymptomatic patient, but may show frank cardiomegaly or pulmonary vascular congestion.

Kidney function is typically evaluated by measurement of serum creatinine levels. Serum electrolyte levels (K) should be determined in patients taking diuretics or digoxin or those with kidney impairment. Mild to moderate hypokalemia (3–3.5 mEq/L) is often seen in patients taking diuretics, but does not have adverse outcome effects. Potassium replacement should be undertaken only in patients who are symptomatic or who are also taking digoxin. Hypomagnesemia is often present and may be a cause of perioperative arrhythmias. Hyperkalemia may be encountered in patients who are taking potassium-sparing diuretics or ACE inhibitors, particularly those with impaired renal function.

Premedication

Mild to moderate preoperative hypertension often resolves following administration of an agent such as midazolam.

INTRAOPERATIVE MANAGEMENT

Objectives

The anesthetic for a hypertensive patient should maintain an appropriately stable blood pressure range. Patients with borderline hypertension may be treated as normotensive patients. Those with long-standing or poorly controlled hypertension, however, have altered autoregulation of cerebral blood flow; higher than normal mean blood pressures may be required to maintain adequate cerebral blood flow. Hypertension, particularly in association with tachycardia, can precipitate or exacerbate myocardial ischemia, ventricular dysfunction, or both. Arterial blood pressure should generally be kept within 20% of preoperative levels.

Monitoring

Most hypertensive patients do not require special intraoperative monitors. Direct intraarterial pressure monitoring should be reserved for patients with wide swings in blood pressure and those undergoing major surgical procedures associated with rapid or marked changes in cardiac preload or afterload. Electrocardiographic monitoring should focus on detecting signs of ischemia. Urinary output should generally be monitored with an indwelling urinary catheter in patients with a preexisting kidney impairment who are undergoing procedures expected to last more than 2 h. Ventricular compliance (see Chapter 20) is typically reduced in patients with ventricular hypertrophy. Excessive intravenous fluid administration in patients with decreased ventricular compliance can also result in elevated pulmonary arterial pressures and pulmonary congestion.

Induction

Induction of anesthesia and endotracheal intubation are often associated with hemodynamic instability in hypertensive patients. Regardless of the level of preoperative blood pressure control, many patients with hypertension display an accentuated hypotensive response to induction of anesthesia, followed by an exaggerated hypertensive response to intubation. Many, if not most, antihypertensive agents and general anesthetics are vasodilators, cardiac depressants, or both. In addition, many hypertensive patients present for surgery in a volume-depleted state. Sympatholytic agents attenuate the normal protective circulatory reflexes, reducing sympathetic tone and unmasking vagal activity.

Hypertensive patients may exhibit severe hypertension during airway manipulation. One of several techniques may be used before intubation to attenuate the hypertensive response:

• Deepening anesthesia with a potent volatile agent

• Administering a bolus of an opioid (fentanyl, 2.5–5 mcg/kg; alfentanil, 15–25 mcg/kg; sufentanil, 0.5–1.0 mcg/kg; or remifentanil, 0.5–1 mcg/kg)

• Administering lidocaine, 1.5 mg/kg intravenously, intratracheally, or topically in the airway

• Achieving β-adrenergic blockade with esmolol, 0.3–1.5 mg/kg; metoprolol 1–5 mg; or labetalol, 5–20 mg

Choice of Anesthetic Agents

A. Induction Agents

The superiority of any one agent or technique over another has not been established. Propofol, barbiturates, benzodiazepines, and etomidate are equally safe for inducing general anesthesia in most hypertensive patients. Ketamine by itself can precipitate marked hypertension; however, it is almost never used as a single agent. When administered with a small dose of another agent, such as a benzodiazepine or propofol, ketamine’s sympathetic stimulating properties can be blunted or eliminated.

B. Maintenance Agents

Anesthesia may be safely maintained with volatile or intravenous agents. Regardless of the primary maintenance technique, addition of a volatile agent or intravenous vasodilator generally allows convenient intraoperative blood pressure control.

C. Vasopressors

Should hypotension develop, a small dose of a direct-acting agent, such as phenylephrine (25–50 mcg), may be beneficial. Patients taking sympatholytics preoperatively may exhibit a decreased response to ephedrine. Vasopressin as a bolus or infusion can also be employed to restore vascular tone in the hypotensive patient.

Intraoperative Hypertension

Intraoperative hypertension not responding to an increase in anesthetic depth (particularly with a volatile agent) can be treated with a variety of parenteral agents (Table 21–6). Readily reversible causes—such as inadequate anesthetic depth, hypoxemia, or hypercapnia—should always be excluded before initiating antihypertensive therapy. Selection of a hypotensive agent depends on the severity, acuteness, and cause of hypertension; the baseline ventricular function; the heart rate; and the presence of bronchospastic pulmonary disease. β-Adrenergic blockade alone or as a supplement is a good choice for a patient with good ventricular function and an elevated heart rate, but is relatively contraindicated in a patient with reactive airway disease. Metoprolol, esmolol, or labetalol is often used intraoperatively. Nicardipine or clevidipine may be preferable to β-blockers for patients with bronchospastic disease. Nitroprusside remains the most rapid and effective agent for the intraoperative treatment of moderate to severe hypertension. Nitroglycerin may be less effective, but is also useful in treating or preventing myocardial ischemia. Fenoldopam, a dopaminergic agonist, is also a useful hypotensive agent; furthermore, it increases renal blood flow. Hydralazine provides sustained blood pressure control, but also has a delayed onset and can cause reflex tachycardia. Reflex tachycardia is not seen with labetalol because of its combined α- and β-adrenergic blockade.

POSTOPERATIVE MANAGEMENT

Postoperative hypertension is common and should be anticipated in patients who have poorly controlled baseline blood pressure. Close blood pressure monitoring should be continued in both the postanesthesia care unit and the early postoperative period. Postoperatively, marked sustained elevations in blood pressure can contribute to the formation of wound hematomas and the disruption of vascular suture lines.

Hypertension in the recovery period is often multifactorial and enhanced by respiratory abnormalities, anxiety and pain, volume overload, bladder distention, or any combination of these. Contributing causes should be corrected and parenteral antihypertensive agents given if necessary. Intravenous labetalol is particularly useful in controlling hypertension and tachycardia, whereas vasodilators are useful in controlling blood pressure in the setting of a slow heart rate. When the patient resumes oral intake, preoperative antihypertensive medications should be restarted.

ISCHEMIC HEART DISEASE

Preoperative Considerations

Myocardial ischemia results from a metabolic oxygen demand that exceeds the oxygen supply. Ischemia can therefore result from increased myocardial metabolic demand, reduced myocardial oxygen delivery, or a combination of both. Common causes include coronary arterial thrombosis or vasospasm; severe hypertension or tachycardia (particularly in the presence of ventricular hypertrophy); severe hypotension, hypoxemia, or anemia; and severe aortic stenosis or regurgitation.

By far, the most common cause of myocardial ischemia is atherosclerosis of the coronary arteries. CAD is responsible for about 25% of all deaths in Western societies and is a major cause of perioperative morbidity and mortality. The overall incidence of CAD in surgical patients is estimated to be between 5% and 10%. Major preoperative risk factors for CAD include hyperlipidemia, hypertension, diabetes, cigarette smoking, increasing age, male sex, and a positive family history. Other risk factors include obesity, a history of cerebrovascular or peripheral vascular disease, menopause, use of high-estrogen oral contraceptives by women who smoke, and a sedentary lifestyle.

CAD may be manifested by symptoms, characteristic electrocardiographic or echocardiographic findings, or biochemical evidence of myocardial necrosis (infarction); symptoms (usually angina) or characteristic echocardiographic or electrocardiographic findings of ischemia; or arrhythmias (including sudden death), symptoms (orthopnea, dyspnea on exertion), signs (rales, dependent edema, shock), or echocardiographic changes suggestive of ventricular dysfunction. An ambulatory patient presenting with risk factors for CAD and new symptoms would normally undergo some form of stress testing to confirm the suspected diagnosis.

Unstable Angina

Unstable angina is defined as (1) an abrupt increase in severity, frequency (more than three episodes per day), or duration of anginal attacks (crescendo angina); (2) angina at rest; or (3) new onset of angina (within the past 2 months) with severe or frequent episodes (more than three per day). Unstable angina may occur following MI or be precipitated by major surgery or by noncardiac medical conditions, including severe anemia, fever, infections, thyrotoxicosis, hypoxemia, and emotional distress in previously stable patients.

Unstable angina, particularly when it is associated with significant ST-segment changes at rest, usually reflects severe underlying coronary disease and may be followed by MI. Plaque disruption with platelet aggregates or thrombi and vasospasm are frequent pathological correlates. Critical stenosis in one or more major coronary arteries is present in more than 80% of patients with these symptoms. Patients with unstable angina require evaluation and treatment, which may include admission to a coronary care unit and some form of coronary intervention.

Chronic Stable Angina

Anginal chest pains are most often substernal, exertional, radiating to the neck or arm, and relieved by rest or nitroglycerin. Variations are common, including epigastric, back, or neck pain, or transient shortness of breath from ventricular dysfunction (anginal equivalent). Nonexertional ischemia and silent (asymptomatic) ischemia are fairly common occurrences, particularly following surgery. Patients with diabetes have an increased incidence of silent ischemia.

Symptoms are generally absent until the atherosclerotic lesions cause 50% to 75% occlusion of the coronary circulation. When a stenotic segment reaches 70% occlusion, maximum compensatory dilation is usually present distally: blood flow may be adequate at rest, but inadequate with increased metabolic demand. An extensive collateral blood supply allows some patients to remain relatively asymptomatic despite severe disease. Coronary vasospasm is also a cause of transient transmural ischemia in some patients; most vasospastic episodes occur at preexisting stenotic lesions in epicardial vessels and may be precipitated by a variety of factors, including emotional upset and hyperventilation (Prinzmetal angina). Coronary spasm is more often observed in patients who have angina with varying levels of activity or emotional stress (variable-threshold); it is less common with classic exertional (fixed-threshold) angina.

The overall prognosis of patients with CAD is related to both the number and severity of coronary obstructions, as well as to the extent of ventricular dysfunction.

Treatment of Ischemic Heart Disease

The general approach in treating patients with ischemic heart disease is five-fold:

• Correction of risk factors, with the hope of slowing disease progression

• Modification of the patient’s lifestyle to reduce stress and improve exercise tolerance

• Correction of complicating medical conditions that can exacerbate ischemia (ie, hypertension, anemia, hypoxemia, hyperthyroidism, fever, infection, or adverse drug effects)

• Pharmacological manipulation of the myocardial oxygen supply–demand relationship

• Anticoagulation

• Correction of coronary lesions by percutaneous coronary intervention (angioplasty [with or without stenting] or atherectomy) or coronary artery bypass surgery

The most commonly used pharmacological agents for stable ischemic heart disease are nitrates, β-blockers, calcium channel blockers, and platelet inhibitors. Those drugs with circulatory effects are compared in Table 21–7.

A. Beta-Adrenergic Blocking Agents

These drugs are first-line agents for patients with stable ischemic heart disease. They decrease myocardial oxygen demand by reducing heart rate and contractility, and, in some cases, afterload (via their antihypertensive effect). In contrast to other agents, they increase survival in patients with impaired left ventricular function, they increase survival after MI, and they reduce the likelihood of a subsequent infarction. Optimal blockade results in a resting heart rate between 50 and 60 beats/min and prevents appreciable increases with exercise (<20 beats/min increase during exercise). Available agents differ in receptor selectivity, intrinsic sympathomimetic (partial agonist) activity, and membrane-stabilizing properties (Table 21–8). Membrane stabilization results in antiarrhythmic activity. Agents with intrinsic sympathomimetic properties are better tolerated by patients with mild to moderate ventricular dysfunction. Certain β-blockers (bisoprolol, carvedilol, and extended-duration metoprolol) improve survival in patients with chronic heart failure. Blockade of β₂-adrenergic receptors also can mask hypoglycemic symptoms in patients with diabetes, delay metabolic recovery from hypoglycemia, and impair the handling of large potassium loads. Cardioselective (β₁-receptor-specific) agents, although generally better tolerated than nonselective agents in patients with reactive airways, must still be used cautiously in such patients. The selectivity of cardioselective agents tends to be dose dependent. Patients on long-standing β-blocker therapy should have these agents continued perioperatively. Acute β-blocker withdrawal in the perioperative period places patients at a markedly increased risk of cardiac morbidity and mortality. β-Blocker therapy should be continued perioperatively in patients who take these agents chronically.

B. Calcium Channel Blockers

These agents are chosen when a patient cannot take a β-blocker or when treatment with a β-blocker is insufficient. The effects and uses of the most commonly used calcium channel blockers are shown in Table 21–9. Calcium channel blockers reduce myocardial oxygen demand by decreasing cardiac afterload and augment myocardial oxygen supply via coronary vasodilation. Verapamil and diltiazem also reduce demand by slowing the heart rate.

Nifedipine’s potent effects on the systemic blood pressure may precipitate hypotension, reflex tachycardia, or both. Its tendency to decrease afterload generally offsets any negative inotropic effect. Long-acting verapamil, diltiazem, amlodipine, or felodipine are preferred. Nicardipine and clevidipine generally have the same effects as nifedipine but are shorter acting, and clevidipine is particularly useful as a vasodilator infusion. Nimodipine is primarily used in preventing cerebral vasospasm following subarachnoid hemorrhage.

All calcium channel blockers potentiate depolarizing and nondepolarizing neuromuscular blocking agents and the circulatory effects of volatile agents. Verapamil and diltiazem can potentiate depression of cardiac contractility and conduction in the atrioventricular (AV) node by volatile anesthetics. Nifedipine and similar agents can potentiate systemic vasodilation by volatile and intravenous agents.

C. Nitrates

Nitrates decrease venous and arteriolar tone, increase vascular capacitance, and reduce ventricular wall tension. These effects tend to reduce myocardial oxygen demand. Prominent venodilation makes nitrates excellent agents when congestive heart failure is also present.

Additionally, nitrates dilate the coronary arteries. Even minor degrees of dilation at stenotic sites may be sufficient to increase blood flow, because flow is directly related to the fourth power of the radius. Nitrate-induced coronary vasodilation preferentially increases subendocardial blood flow in ischemic areas. This favorable redistribution of coronary blood flow to ischemic areas may be dependent on the presence of collaterals in the coronary circulation.

Nitrates can be used for both the treatment of acute ischemia and prophylaxis against frequent anginal episodes.

D. Anticoagulants

Chronic aspirin therapy reduces coronary events in patients with CAD and prevents coronary and ischemic cerebral events in at-risk patients. Other platelet antagonists are generally also included in patients who have undergone percutaneous coronary stenting. Careful review of anticoagulant/antiplatelet medications is a mandatory element of preanesthetic assessment, especially if neuraxial anesthesia is being considered (see Chapter 45).

E. Other Agents and Other Treatments

ACE inhibitors prolong survival in patients with congestive heart failure or left ventricular dysfunction. Antiarrhythmic therapy in patients with complex ventricular ectopy who have significant CAD and left ventricular dysfunction should be guided by an electrophysiological study. Patients with inducible sustained ventricular tachycardia (VT) or ventricular fibrillation are candidates for an automatic internal cardioverter-defibrillator (ICD). Treatment of ventricular ectopy (with the exception of sustained VT) in patients with good ventricular function does not improve survival and may increase mortality. In contrast, ICDs have been shown to improve survival in patients with advanced cardiomyopathy (ejection fraction <30%), even in the absence of demonstrable arrhythmias.

E. Combination Therapy

Moderate to severe angina frequently requires combination therapy with two or more classes of agents. Patients with ventricular dysfunction may not tolerate the combined negative inotropic effect of a β-blocker and a calcium channel blocker together; an ACE inhibitor or ARB is better tolerated and seems to improve survival. Similarly, the additive effect of a β-blocker and a calcium channel blocker on the AV node may precipitate heart block in susceptible patients.

PREOPERATIVE MANAGEMENT

The importance of ischemic heart disease—particularly a history of MI—as a risk factor for perioperative morbidity and mortality is reviewed earlier in this chapter. Most studies confirm that perioperative outcome is related to disease severity, ventricular function, and the type of surgery to be undertaken. Patients with extensive (three-vessel or left main) CAD, a recent history of MI, or ventricular dysfunction are at greatest risk of cardiovascular complications. As previously mentioned, current guidelines recommend revascularization only when such treatment would be indicated irrespective of the patient’s need for surgery.

Chronic stable (mild to moderate) angina does not seem to increase perioperative risk substantially. Similarly, a history of prior coronary artery bypass surgery or coronary angioplasty alone does not seem to substantially increase perioperative risk. In some studies, maintenance of chronic β-receptor blockers in the perioperative period has been shown to reduce perioperative mortality and the incidence of postoperative cardiovascular complications; however, other studies have shown an increase in stroke and death following preoperative introduction of β-blockers to at-risk patients. Consequently, initiating therapy with β-blockers in at-risk patients who will undergo surgery is no longer recommended. Like β-blockers, statins should be continued perioperatively in patients so routinely treated, as acute perioperative withdrawal of statins is associated with adverse outcomes. The ACC/AHA recommendations are summarized in a set of useful guidelines that also provide guidance on the timing of surgery following percutaneous coronary interventions and the deployment of coronary stents (Table 21–10).

History

The most important symptoms to elicit include chest pain, dyspnea, poor exercise tolerance, syncope, or near syncope. The relationship between symptoms and activity level should be established. Activity should be described in terms of everyday tasks, such as walking or climbing stairs. Patients may be relatively asymptomatic despite severe CAD if they have a sedentary lifestyle. Patients with diabetes are particularly prone to silent ischemia. Easy fatigability or shortness of breath suggests impaired ventricular function.

A history of unstable angina or MI should include the time of its occurrence and whether it was complicated by arrhythmias, conduction disturbances, or heart failure. Arrhythmias and conduction abnormalities are more common in patients with previous infarction and in those with poor ventricular function. This latter group of patients will often have ICDs.

Physical Examination & Routine Laboratory Evaluation

Evaluation of patients with CAD is similar to that of patients with hypertension. Laboratory evaluation in patients who have a history compatible with recent unstable angina and are undergoing emergency procedures should include cardiac enzymes. Normal serum levels of troponins, creatine kinase (MB isoenzyme), and lactate dehydrogenase (type 1 isoenzyme) are useful in excluding MI.

The baseline ECG is normal in 25% to 50% of patients with CAD but no prior MI. Electrocardiographic evidence of ischemia often becomes apparent only during angina. The most common baseline abnormalities are nonspecific ST-segment and T-wave changes. Prior infarction may be manifested by Q waves or loss of R waves in the leads closest to the infarct. First-degree AV block, bundle-branch block, or hemiblock may be present. Persistent ST-segment elevation following MI may be indicative of a left ventricular aneurysm. A long rate-corrected QT interval (QT_c > 0.44 s) may reflect the underlying ischemia, drug toxicity (usually class Ia antiarrhythmic agents, antidepressants, or phenothiazines), electrolyte abnormalities (hypokalemia or hypomagnesemia), autonomic dysfunction, mitral valve prolapse, or, less commonly, a congenital abnormality. Patients with a long QT interval are at risk of developing ventricular arrhythmias—particularly polymorphic VT (torsades de pointes), which can lead to ventricular fibrillation. The long QT interval reflects nonuniform prolongation of ventricular repolarization and predisposes patients to reentry phenomena. In contrast to polymorphic ventricular arrhythmias with a normal QT interval, which respond to conventional antiarrhythmics, polymorphic tachyarrhythmias with a long QT interval generally respond best to pacing or magnesium salts.

The chest radiograph can be used to exclude cardiomegaly or pulmonary vascular congestion secondary to ventricular dysfunction.

Specialized Studies

A. Holter Monitoring

Continuous ambulatory electrocardiographic (Holter) monitoring is useful in evaluating arrhythmias, antiarrhythmic drug therapy, and severity and frequency of ischemic episodes. Silent (asymptomatic) ischemic episodes are frequently found in patients with CAD. Frequent ischemic episodes on preoperative Holter monitoring correlate well with intraoperative and postoperative ischemia. Holter monitoring showing no ischemic episodes has an excellent negative predictive value for postoperative cardiac complications.

B. Exercise Electrocardiography

The usefulness of this test without associated cardiac imaging is limited in patients with baseline ST-segment abnormalities and those who are unable to increase their heart rate (>85% of maximal predicted) because of fatigue, dyspnea, or drug therapy. Overall sensitivity is 65%, and specificity is 90%. Exercise testing is most sensitive (85%) in patients with three-vessel or left main CAD. Disease that is limited to the left circumflex artery may also be missed because ischemia in its distribution may not be evident on the standard surface ECG. A normal test does not necessarily exclude CAD, but suggests that severe disease is not likely. The degree of ST-segment depression, its severity and configuration, the time of onset in the test, and the time required for resolution are important findings. A myocardial ischemic response at low levels of exercise is associated with a significantly increased risk of perioperative complications and long-term cardiac events. Other significant findings include changes in blood pressure and the occurrence of arrhythmias. Exercise-induced ventricular ectopy frequently indicates severe CAD associated with ventricular dysfunction. The ischemia presumably leads to electrical instability in myocardial cells. Given that risk seems to be associated with the extent of potentially ischemic myocardium, testing often includes perfusion scans or echocardiographic assessments; however, in ambulatory patients, exercise ECG testing alone is useful because it estimates functional capacity and detects myocardial ischemia.

C. Myocardial Perfusions Scans and Other Imaging Techniques

Myocardial perfusion imaging using thallium-201 or technetium-99m is used in evaluating patients who cannot exercise (eg, peripheral vascular disease) or who have underlying ECG abnormalities that preclude interpretation during exercise (eg, left bundle-branch block). If the patient cannot exercise, images are obtained before and after injection of an intravenous coronary dilator (eg, dipyridamole or adenosine) to produce a hyperemic response similar to exercise. Myocardial perfusion studies following exercise or injection of dipyridamole or adenosine have a high sensitivity, but only fairly good specificity for CAD. They are best for detecting two- or three-vessel disease. These scans can locate and quantitate areas of ischemia or scarring and differentiate between the two. Perfusion defects that fill in on the redistribution phase represent ischemia, not previous infarction. The negative predictive value of a normal perfusion scan is approximately 99%.

Magnetic resonance imaging, positron emission tomography, and computed tomography scans are increasingly being used to define coronary artery anatomy and determine myocardial viability.

D. Echocardiography

This technology provides information about both regional and global ventricular function and may be carried out at rest, following exercise, or with administration of dobutamine. Detectable regional wall motion abnormalities and the derived left ventricular ejection fraction correlate well with angiographic findings. Moreover, dobutamine stress echocardiography seems to be a reliable predictor of adverse cardiac complications in patients who cannot exercise. New or worsening wall motion abnormalities following dobutamine infusion are indicative of significant ischemia. Patients with an ejection fraction of less than 50% tend to have more severe disease and increased perioperative morbidity. Dobutamine stress echocardiography, however, may not be reliable in patients with left bundle-branch block because septal motion may be abnormal, even in the absence of left anterior descending CAD in some patients.

E. Coronary Angiography

Coronary angiography remains the definitive way to evaluate CAD and is associated with a low complication rate (<1%). The location and severity of occlusions can be defined, and coronary vasospasm may also be observed on angiography. In evaluating fixed stenotic lesions, occlusions greater than 50% to 75% are generally considered significant. The severity of disease is often expressed according to the number of major coronary vessels affected (one-, two-, or three-vessel disease). Significant stenosis of the left main coronary artery is of great concern because disruption of flow in this vessel will have adverse effects on almost the entire left ventricle.

Ventriculography, measurement of the ejection fraction, and measurement of intracardiac pressures, also provide important information. Indicators of significant ventricular dysfunction include an ejection fraction less than 50%, a left ventricular end-diastolic pressure greater than 18 mm Hg, a cardiac index less than 2.2 L/min/m², and marked or multiple wall motion abnormalities.

Premedication

Allaying fear, anxiety, and pain preoperatively are desirable goals in patients with CAD. Satisfactory premedication minimizes sympathetic activation, which adversely affects the myocardial oxygen supply–demand balance. Overmedication is equally detrimental and should be avoided because it may result in hypoxemia, respiratory acidosis, and hypotension. Most clinicians now limit premedication to small doses of intravenous midazolam (or the equivalent) given immediately before invasive procedures or before transporting the patient to the operating theater.

Preoperative medications should generally be continued until the time of surgery. The sudden withdrawal of antianginal medication perioperatively—particularly β-blockers—can precipitate a sudden, rebound increase in ischemic episodes. Statins should also be continued in the perioperative period. Prophylactic administration of nitrates intravenously or transdermally to patients with CAD in the perioperative period provides no benefit to patients not previously on long-term nitrate therapy and without evidence of ongoing ischemia. Transdermal absorption of nitroglycerin may be erratic in the perioperative period.

INTRAOPERATIVE MANAGEMENT

The intraoperative period is regularly associated with factors and events that can adversely affect the myocardial oxygen demand–supply relationship. Activation of the sympathetic system plays a major role. Hypertension and enhanced contractility increase myocardial oxygen demand, whereas tachycardia increases demand and reduces supply. Although myocardial ischemia is commonly associated with tachycardia, ischemia can occur in the absence of any apparent hemodynamic derangement.

Objectives

The overwhelming priority in managing patients with ischemic heart disease is maintaining a favorable myocardial supply–demand relationship. Autonomic-mediated increases in heart rate and blood pressure should be controlled with deeper planes of general anesthesia, adrenergic blockade, vasodilators, or a combination of these. Excessive reductions in coronary perfusion pressure or arterial oxygen content must be avoided. Higher diastolic pressures may be preferable in patients with high-grade coronary occlusions. Excessive increases—such as those caused by fluid overload—in left ventricular end-diastolic pressure should be avoided because they increase ventricular wall tension (afterload) and can reduce subendocardial perfusion (see Chapter 20). Transfusion carries its own risks and consequently there is no set transfusion trigger in patients with CAD; however, most clinicians are reluctant to have hemoglobin levels fall below 7 g/dL. Anemia can lead to tachycardia, worsening the balance between myocardial oxygen supply and demand. The ACC/AHA recommendations for the anesthetic management of the patient with CAD disease for noncardiac surgery are summarized in Table 21–11.

MONITORING

Intraarterial pressure monitoring is reasonable in most patients with severe CAD and major or multiple cardiac risk factors who are undergoing any but the most minor procedures. Central venous (or rarely pulmonary artery) pressure can be monitored during prolonged or complicated procedures involving large fluid shifts or blood loss. Noninvasive methods of cardiac output determination and volume assessment have been previously discussed in this text and we recommend them. Transesophageal echocardiography (TEE) and transthoracic echocardiography (TTE) can provide valuable information, both qualitative and quantitative, on contractility and ventricular chamber size (preload) perioperatively.

A. Electrocardiography

Early ischemic changes are subtle and involve changes in T-wave morphology, including inversion, tenting, or both (Figure 21–2). More obvious ischemia may be seen in the form of progressive ST-segment depression. Down-sloping and horizontal ST depressions are of greater specificity for ischemia than is up-sloping depression. New ST-segment elevations are rare during noncardiac surgery and are indicative of severe ischemia, vasospasm, or infarction.

It should be noted that an isolated minor ST elevation in the mid-precordial leads (V₃ and V₄) can be a normal variant in young patients. Ischemia may also present as an unexplained intraoperative atrial or ventricular arrhythmia or the onset of a new conduction abnormality. The sensitivity of the ECG in detecting ischemia is related to the number of leads monitored. Studies suggest that the V₅, V₄, II, V₂, and V₃ leads (in decreasing sensitivity) are most useful. Ideally, at least two leads should be monitored simultaneously. Usually, lead II is monitored for inferior wall ischemia and arrhythmias, and V₅ is monitored for anterior wall ischemia. When only one lead can be monitored, a modified V₅ lead provides the greatest sensitivity.

The increasing number of individuals treated with drug-eluting stents can be problematic perioperatively, especially when antiplatelet therapy must be discontinued (eg, emergency spinal surgery). Such patients are at very increased risk of thrombosis and perioperative MI. Anesthesia providers should never for nonsurgical reasons (eg, desire to perform a spinal anesthetic) discontinue antiplatelet or antithrombotic agents perioperatively without first discussing the risks and benefits of the proposed anesthetic requiring suspension of antiplatelet therapy with the patient and his or her cardiologist. The ACC/AHA guidelines offer recommendations on the approach of bringing patients to surgery following percutaneous coronary interventions and the type of interventions suggested when subsequent surgery is expected (Figure 21–3).

B. Hemodynamic Monitoring

The most common hemodynamic abnormalities observed during ischemic episodes are hypertension and tachycardia. They are almost always a cause (rather than the result) of ischemia. Hypotension is a late and ominous manifestation of progressive ventricular dysfunction. TEE readily will demonstrate a dysfunctional ventricle and ventricular wall motion changes associated with myocardial ischemia. Ischemia is frequently, but not always, associated with an abrupt increase in pulmonary capillary wedge pressure; however, it is rare for pulmonary capillary wedge pressure to be measured during general anesthesia.

C. Transesophageal Echocardiography

TEE can be helpful in detecting global and regional cardiac dysfunction, as well as valvular function, in surgical patients. Moreover, detection of new regional wall motion abnormalities is a more sensitive and earlier indication of myocardial ischemia than the ECG. In animal studies in which coronary blood flow is gradually reduced, regional wall motion abnormalities develop before the ECG changes. Although the occurrence of new intraoperative abnormalities correlates with postoperative MIs in some studies, not all such abnormalities are necessarily ischemic. Both regional and global abnormalities can be caused by changes in heart rate, altered conduction, preload, afterload, or drug-induced changes in contractility. Decreased systolic wall thickening may be a more reliable index for ischemia than endocardial wall motion alone.

Arrhythmias, Pacemakers, and Internal Cardioverter-Defibrillator Management

Electrolyte disorders, heart structure defects, inflammation, myocardial ischemia, cardiomyopathies, and conduction abnormalities can all contribute to the development of perioperative arrhythmias and heart block. Consequently, anesthesia providers must be prepared to treat both chronic and new-onset cardiac rhythm abnormalities.

Supraventricular tachycardias (SVTs) can have hemodynamic consequences secondary to loss of AV synchrony and decreased diastolic filling time. Loss of the “P” wave on the ECG with a fast ventricular response is consistent with SVTs. Most SVTs occur secondary to a reentrant mechanism. Reentrant arrhythmias occur when conduction tissues in the heart depolarize or repolarize at varying rates. In this manner, a self-perpetuating loop of repolarization and depolarization can occur in the conduction pathways or AV node, or both. SVTs producing hemodynamic collapse are treated perioperatively with synchronized cardioversion. Adenosine can likewise be given to slow AV node conduction and potentially disrupt the reentrant loop. SVTs in patients without accessory conduction bundles (Wolff–Parkinson–White [WPW] syndrome) are treated with β-blockers and calcium channel blockers. In patients with known WPW, procainamide or ibutilide can be used to treat SVTs. Use of intravenous amiodarone, adenosine, digoxin, or non-dihydropyridine calcium channel antagonists is considered a class III recommendation by the AHA/ACC as these agents may harmfully increase the ventricular response in patients with preexcitation syndromes such as WPW. At times, SVTs manifest with a broad QRS complex and seem to be similar to VTs. Such rhythms, when they present, should be treated like VT, until proven otherwise.

Atrial fibrillation (AF) can complicate the perioperative period (Figure 21–4). Up to 35% of cardiac surgery patients develop postoperative AF.

The ACC/AHA guidelines recommend antithrombotic therapy in patients with long-standing AF to prevent thromboembolic ischemic stroke. Consequently, many patients with AF will present to the operating room on some form of antithrombotic therapy (eg, warfarin, direct thrombin, or factor Xa inhibitors). Patients may require discontinuation of oral anticoagulation therapy prior to invasive procedures. Bridging with heparin is often utilized in patients at high risk for thromboembolism (eg, patients with mechanical heart valves).

When AF develops perioperatively, rate control with β-blockers can often be instituted. Chemical cardioversion can be attempted with amiodarone or procainamide. Of note, if the duration of AF is greater than 48 hours, or unknown, ACC/AHA guidelines recommend anticoagulation for 3 weeks prior to, and 4 weeks following, either electrical or chemical cardioversion. Additionally, TEE can be performed to rule out the presence of left atrial or left atrial appendage thrombus.

Should AF develop postoperatively, ventricular rate response can be controlled with AV nodal blocking agents, unless contraindicated. Should AF result in hemodynamic instability, synchronized cardioversion should be attempted. Patients at high risk of AF following cardiac surgery can be treated with prophylactic amiodarone. Many centers routinely administer β-blockers or amiodarone to all patients undergoing coronary artery surgery to reduce the risk of new onset AF.

AF is most frequently associated with loss of atrial muscle and the development of fibrosis. Fibrosis may contribute to reentrant mechanisms of AF as depolarization/repolarization becomes nonhomogeneous. AF may also develop from a focal source often located in the pulmonary veins. In patients with an accessory bundle, AF can produce rapid ventricular responses and hemodynamic collapse. Drugs that slow conduction across the AV node (eg, digitalis, verapamil, diltiazem) do not slow conduction across the accessory pathway, potentially leading to hemodynamic collapse. The ACC/AHA guidelines likewise recommend caution in the use of β-blockers for AF in patients with preexcitation syndromes.

Ventricular arrhythmias have been the subject of much review by the AHA (Table 21–12). Ventricular premature contractions (VPCs) can appear perioperatively secondary to electrolyte abnormalities (hypokalemia, hypomagnesium, hypocalcemia), acidosis, ischemia, embolic phenomenon, mechanical irritation of the heart from central lines, cardiac manipulation, and drug effects. Correction of the underlying source of any arrhythmia should be addressed. Patients can likewise present with VPCs secondary to various cardiomyopathies.

The incidence of sudden cardiac death (SCD) is estimated at 1 to 2/1000 per year. Consequently, some patients will experience an unexpected death in the perioperative period. All anesthesia providers must be prepared to resuscitate and manage patients with ventricular arrhythmias, including ventricular tachycardia (VT) (nonsustained and sustained) and ventricular fibrillation.

Nonsustained VT is a short run of ventricular ectopy that lasts <30 s and spontaneously terminates, whereas sustained VT persists longer than 30 s. VT is either monomorphic or polymorphic, depending on the QRS complex. If the QRS complex morphology changes, it is designated as polymorphic VT. Torsades des pointes is a form of VT associated with a prolonged QT interval, producing a sine wave-like VT pattern on the ECG. Ventricular fibrillation requires immediate resuscitative efforts and defibrillation.

Patients presenting with ventricular ectopy and nonsustained runs of VT routinely undergo investigation prior to surgery; however, patients with such rhythm abnormalities may not be at greater risk for nonfatal MI or cardiac death perioperatively. Supraventricular and ventricular arrhythmias constitute active cardiac conditions that warrant evaluation and treatment prior to elective, noncardiac surgery. Electrophysiological studies are undertaken to determine the possibility for catheter-mediated ablation of VTs.

Should VT present perioperatively, cardioversion is recommended whenever hemodynamic compromise occurs. Otherwise, treatment with amiodarone or procainamide can be attempted. At all times, therapy should also be directed at identifying any causative sources of the arrhythmia. β-Blockers are useful in the treatment of VT, especially if ischemia is a suspected causative factor in the development of rhythm. The use of β-blockers following MI has reduced the incidence of post-MI ventricular fibrillation.

Torsades des pointes is associated with conditions that lengthen the QT interval. If the arrhythmia develops in association with pauses, pacing can be effective. Likewise, some patients may benefit from isoproterenol infusions, if they develop pause-dependent torsades des pointes. Magnesium sulfate may be useful in patients with long QT syndrome and episodes of torsades.

The development of perioperative ventricular fibrillation requires defibrillation and the use of resuscitation algorithms. Amiodarone can be used to stabilize the rhythm following successful defibrillation.

ICDs are recommended in patients with a history of survived SCD, decreased ventricular function following MI, and left ventricular ejection fractions less than 35%. Additionally, ICDs are used to treat potential sudden cardiac death in patients with dilated, hypertrophic, arrhythmogenic right ventricular and genetic cardiomyopathies. ICDs usually have a biventricular pacing function that improves the effectiveness of left ventricular contraction. Patients with heart failure frequently have a widened QRS complex greater than 120 ms. In such patients, ventricular systole is less efficient, as the lateral and septal left ventricular walls do not effectively contract because of the conduction delay. Cardiac resynchronization therapy has been shown to improve functional status in patients with heart failure.

Anesthetic management for the placement of ICDs and other electrophysiological procedures (eg, catheter ablation) depends on the patient’s underlying conditions. Many patients present with systolic and diastolic heart failure and depend on sympathetic tone to maintain blood pressure. Some patients tolerate ICD placement using deep sedation rather than general anesthesia. However, catheter-based electrophysiological studies can be quite time consuming, and patients can develop atelectasis and airway obstruction. Thus, general anesthesia is often used in the electrophysiology laboratory. Should the patient’s blood pressure suddenly decline during electrophysiologic studies, development of pericardial tamponade should be suspected. Emergent drainage of tamponade may be necessary.

Many patients present to surgery with ICDs in place. Published guidelines of the American Society of Anesthesiologists can provide assistance in the management of such patients. Management is a three-step process, as follows:

1. Preoperative. Identify the type of device and determine if it is used for antibradycardia functions. Consult with the patient’s cardiologist preoperatively as to the device’s function and use history.

2. Intraoperative. Determine what electromagnetic interference is likely to present intraoperatively and advise the use of bipolar electrocautery where possible. Assure the availability of temporary pacing and defibrillation equipment and apply pads as necessary. Patients who are pacemaker-dependent can be programmed to an asynchronous mode to mitigate electrical interference. Magnet application to ICDs may disable the antitachycardia function, but not convert to an asynchronous pacemaker. Consultation with the patient’s cardiologist and interrogation of the device is often necessary. Most patients will have a card on which the device model and manufacturer are provided. A telephone call to the device manufacturer can provide information about device performance and the best method for managing the device (eg, reprogramming or applying a magnet) prior to surgery. A large number of ICD models are in use; however, most suspend their antitachycardia function in response to a magnet.

3. Postoperative. The device must be interrogated to ensure that therapeutic functions have been restored. Patients should be continuously monitored until the antitachycardia functions of the device are restored and its function has been confirmed.

ICDs are particularly problematic intraoperatively when electrocautery is used because the device may (1) interpret cautery as ventricular fibrillation; (2) inhibit pacemaker function due to cautery artifact; (3) increase the pacing rate due to activation of a rate-responsive sensor; or (4) temporarily or permanently reset to a backup or reset mode. Use of bipolar cautery, placement of the grounding pad far from the ICD device, and limiting use of the cautery to only short bursts help to reduce the likelihood of problems, but will not eliminate them.

When there is greater risk of stray currents from the cautery, the ICD device should have the defibrillator function programmed off immediately before surgery and reprogrammed back on immediately afterward. External defibrillation pads should be applied and attached to a defibrillator machine intraoperatively. Careful monitoring of the arterial pulse with pulse oximetry or an arterial waveform is necessary to ensure that the pacemaker is not inhibited and that there is arterial perfusion during episodes of ECG artifact from surgical cautery.

HEART FAILURE

An increasing number of patients present for surgery with either systolic or diastolic heart failure. Heart failure may be secondary to ischemia, valvular heart disease, infectious agents, or many forms of cardiomyopathy. Patients may experience heart failure symptoms with both a preserved and reduced ejection fractions. Most heart failure patients seek medical attention for complaints of dyspnea and fatigue. Heart failure develops over time, as symptoms worsen (Figure 21–5). Patients generally undergo echocardiography to diagnose structural heart defects, to detect signs of cardiac “remodeling,” to determine the left ventricular ejection fraction, and to assess the heart’s diastolic function. Laboratory evaluations of concentration of brain natriuretic peptide (BNP) are likewise obtained to distinguish heart failure from other causes of dyspnea. BNP is released from the heart, and its elevation is associated with impaired ventricular function.

The body attempts to compensate for LV systolic failure through activation of the sympathetic and renin–angiotensin–aldosterone system. Consequently, patients experience salt retention, volume expansion, sympathetic stimulation, and vasoconstriction. The heart dilates to maintain stroke volume in spite of decreased contractility. Over time, compensatory mechanisms fail and contribute to the symptoms associated with heart failure (eg, dependent edema, tachycardia, decreased tissue perfusion). Patients with systolic heart failure are likely to present to surgery having been previously treated with diuretics, β-blockers, ACE inhibitors or ARBs, and possibly aldosterone antagonists. Electrolytes must be measured, as diuretics frequently lead to hypokalemia. ARB or ACE inhibitor use may contribute to hypotension in the surgical patient with heart failure. ACE inhibitors are rarely associated with angioedema requiring emergent airway management.

Myocardial relaxation is a dynamic, not passive, process. The heart with preserved diastolic function accommodates volume during diastole, with minimal increases in left ventricular end-diastolic pressure. Conversely, the heart with diastolic dysfunction relaxes poorly and produces increased left ventricular end-diastolic pressure. The increased left ventricular end-diastolic pressure is transmitted to the left atrium and pulmonary vasculature resulting in symptoms of congestion. Patients with any form of heart failure have increased risk of perioperative morbidity.

HYPERTROPHIC CARDIOMYOPATHY

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant trait that affects 1 in 500 adults. Many patients are unaware of the condition, and some will present with sudden cardiac death as the initial manifestation. Symptoms include dyspnea, exercise intolerance, palpitations, and chest pain. Clinically, HCM is detected by the murmur of dynamic left ventricular outflow tract (LVOT) obstruction in late systole. Symptomatic patients frequently have a thickened intraventricular septum of 20 to 30 mm. A variety of genetic variants have been identified as causative. The myocardium of the intraventricular septum is abnormal, and many patients can develop diastolic dysfunction without pronounced dynamic obstructive gradients. During systole, the anterior leaflet of the mitral valve abuts the intraventricular septum (Figure 21–6), producing obstruction and a late systolic murmur.

Perioperative management is aimed at minimizing the degree of LVOT obstruction. This is accomplished by maintaining adequate intravascular volume, avoiding vasodilatation, and reducing myocardial contractility through the use of β-blockers.

1. General Evaluation of Patients

Regardless of the lesion or its cause, preoperative evaluation should be primarily concerned with determining the identity and severity of the lesion and its hemodynamic significance, ventricular function, and the presence of any secondary effects on pulmonary, renal, or hepatic function. Concomitant CAD should not be overlooked, particularly in older patients and those with known risk factors (see earlier discussion). Myocardial ischemia may occur in the absence of significant coronary occlusion in patients with severe aortic stenosis or regurgitation.

History

One should evaluate exercise tolerance, fatigability, pedal edema, and shortness of breath in general (dyspnea), when lying flat (orthopnea), or at night (paroxysmal nocturnal dyspnea). The New York Heart Association functional classification of heart disease (Table 21–13) is useful for grading the severity of heart failure symptoms and estimating prognosis. Patients should also be questioned about chest pains and neurological symptoms. Some valvular lesions are associated with thromboembolic phenomena. Prior procedures, such as valvotomy or valve replacement and their effects, should also be well documented.

Medications commonly used by valvular heart disease patients include diuretics, vasodilators, ACE inhibitors, β-blockers, antiarrhythmics, and anticoagulants. Preoperative vasodilator therapy may be used to decrease preload, afterload, or both. Excessive vasodilation worsens exercise tolerance and is often first manifested as postural (orthostatic) hypotension.

Physical Examination

The most important signs to identify on physical examination are those of congestive heart failure. Left-sided (S₃ gallop or pulmonary rales) and right-sided (jugular venous distention, hepatojugular reflux, hepatosplenomegaly, or pedal edema) signs may be present. Auscultatory findings may suggest valvular dysfunction, but echocardiographic studies are more reliable. The ACC/AHA guidelines recommend that transthoracic echocardiography be performed as a class I indication in the initial evaluation of patients suspected of having valvular heart disease. Moreover, the ACC/AHA suggest that any change in symptoms or physical examination findings warrants a repeat transthoracic echocardiography exam. Neurological deficits, usually secondary to embolic phenomena, should be documented.

Laboratory Evaluation

In addition to the laboratory studies discussed for patients with hypertension and CAD, liver function tests may be useful in assessing hepatic dysfunction caused by passive hepatic congestion in patients with severe or chronic right-sided failure. Adequate reversal of warfarin or heparin anticoagulation may be documented with a prothrombin time and international normalized ratio (INR) or partial thromboplastin time, respectively, prior to surgery.

Electrocardiographic findings are generally nonspecific. The chest radiograph is useful to assess cardiac size and pulmonary vascular congestion.

Special Studies

Echocardiography, imaging studies, and cardiac catheterization should only be obtained if the results will change therapy or outcomes. In many instances, noninvasive studies obviate the need for cardiac catheterization, unless there are concerns about CAD. When advanced imaging procedures are performed, they generally address the following questions:

• Which valvular abnormality is most important hemodynamically?

• What is the severity of an identified lesion?

• What degree of ventricular impairment is present?

• What is the hemodynamic significance of other identified abnormalities?

• Is there any evidence of CAD?

The ACC/AHA have prepared detailed guidelines to assist in the management of patients with valvular heart disease. Although the evaluation of the patient with a heart murmur generally rests with the cardiologist, anesthesia providers will on occasion discover a previously undetected murmur on preanesthetic examination. In particular, anesthetists are concerned that undiagnosed, critical aortic stenosis might be present, which could potentially lead to hemodynamic collapse with either regional or general anesthesia. In the past, most valvular heart diseases were a consequence of rheumatic heart disease; however, with an aging surgical population, increasing numbers of patients have degenerative valve problems. More than one in eight patients older than age 75 years may manifest at least one form of moderate to severe valvular heart disease. A study conducted in the Netherlands reported that the prevalence of aortic stenosis was 2.4% in patients older than age 60 years who were scheduled for elective surgery.

Murmurs occur as a consequence of the accelerated blood flow through narrowed openings in stenotic and regurgitant lesions. Although systolic murmurs may be related to increased blood flow velocity, the ACC/AHA guidelines note that all diastolic and continuous murmurs reflect pathology. When new murmurs are detected in a preoperative evaluation, consultation with the patient’s personal physician is helpful to determine the need for echocardiographic evaluation. In many centers, immediate echocardiographic evaluation can be performed in the preoperative area, often by another member of the anesthesia department.

2. Specific Valvular Disorders

MITRAL STENOSIS

Preoperative Considerations

Mitral stenosis almost always occurs as a delayed complication of rheumatic fever. However, mitral stenosis can also occur in dialysis-dependent patients. Two-thirds of patients with mitral stenosis are female. The stenotic process is estimated to begin after a minimum of 2 years following rheumatic heart disease and results from progressive fusion and calcification of the valve leaflets. Symptoms generally develop after 20 to 30 years, when the mitral valve orifice is reduced from its normal 4 to 6 cm² opening to less than 1.5 cm². Less than 50% of patients have isolated mitral stenosis; the remaining patients also have mitral regurgitation, and up to 25% of patients also have rheumatic involvement of the aortic valve (stenosis or regurgitation).

Pathophysiology

The rheumatic process causes the valve leaflets to thicken, calcify, and become funnel shaped; annular calcification may also be present. The mitral commissures fuse, the chordae tendineae fuse and shorten, and the valve cusps become rigid; as a result, the valve leaflets typically display bowing or doming during diastole on echocardiography.

Significant restriction of blood flow through the mitral valve results in a transvalvular pressure gradient that depends on cardiac output, heart rate (diastolic time), and cardiac rhythm. Increases in either cardiac output or heart rate (decreased diastolic time) necessitate higher flows across the valve and result in higher transvalvular pressure gradients. The left atrium is often markedly dilated, promoting SVTs, particularly AF. Blood flow stasis in the atrium promotes the formation of thrombi, usually in the left atrial appendage. Loss of normal atrial systole with AF (which is usually responsible for 20% to 30% of ventricular filling) necessitates even higher diastolic flow across the valve to maintain the same cardiac output and increases the transvalvular gradient.

Acute elevations in left atrial pressure are rapidly transmitted back to the pulmonary capillaries. If mean pulmonary capillary pressure acutely and significantly rises transudation of capillary fluid may result in pulmonary edema. Chronic elevations in pulmonary capillary pressure are partially compensated by increases in pulmonary lymph flow, but eventually result in pulmonary vascular changes, leading to irreversible increases in pulmonary vascular resistance (PVR) and pulmonary hypertension. Reduced lung compliance and a secondary increase in the work of breathing contribute to chronic dyspnea. Right ventricular failure is frequently precipitated by acute or chronic elevations in right ventricular afterload. Marked dilation of the right ventricle can result in tricuspid or pulmonary valve regurgitation.

Embolic events are common in patients with mitral stenosis and AF. Dislodgment of clots from the left atrium results in systemic emboli, commonly to the cerebral circulation. Patients also have an increased incidence of pulmonary emboli, pulmonary infarction, hemoptysis, and recurrent bronchitis. Chest pain occurs in 10% to 15% of patients with mitral stenosis, even in the absence of CAD; its cause often remains unexplained but may be emboli in the coronary circulation or acute right ventricular pressure overload. Patients may develop hoarseness as a result of compression of the left recurrent laryngeal nerve by the enlarged left atrium.

Left ventricular function is preserved in the majority of patients with pure mitral stenosis (Figure 21–7); however, impaired left ventricular function may be encountered in up to 25% of patients and presumably represents residual damage from rheumatic myocarditis or coexistent hypertensive or ischemic heart disease.

The left ventricle is chronically underloaded in the patient with mitral stenosis and the stroke volume may be reduced. At the same time, the left atrium, right ventricle, and right atrium are frequently dilated and dysfunctional. Vasodilation that occurs following both neuraxial and general anesthesia can lead to peripheral venous blood pooling and inadequate volume delivery to the left ventricle. This can precipitate hemodynamic collapse.

Treatment

The time from onset of symptoms to incapacitation averages 5 to 10 years. At that stage, most patients die within 2 to 5 years. Surgical correction is therefore usually undertaken once significant symptoms develop. Percutaneous transseptal balloon valvuloplasty may be used in selected young or pregnant patients, as well as older patients who are poor surgical candidates. Medical management is primarily supportive and includes limitation of physical activity, sodium restriction, and diuretics. Small doses of a β-adrenergic blocking drug may also be useful in controlling heart rate in patients with mild to moderate symptoms. Patients with a history of emboli and those at high risk (age older than 40 years; a large atrium with chronic atrial fibrillation) are usually anticoagulated.

Anesthetic Management

A. Objectives

The principal hemodynamic goals are to maintain a sinus rhythm (if present preoperatively) and to avoid tachycardia, large increases in cardiac output, and both hypovolemia and fluid overload by judicious administration of intravenous fluids.

B. Monitoring

Invasive hemodynamic monitoring is often used for major surgical procedures, particularly those associated with large fluid shifts. TEE and noninvasive cardiac output monitors can also be used to help guide perioperative management. Overzealous fluid replacement readily precipitates pulmonary edema in patients with severe disease. Pulmonary capillary wedge pressure measurements in the presence of mitral stenosis reflect the transvalvular gradient and not necessarily left ventricular end-diastolic pressure. Prominent a waves and a decreased y descent are typically present on the pulmonary capillary wedge pressure waveform in patients who are in sinus rhythm. A prominent cv wave on the central venous pressure waveform is usually indicative of secondary tricuspid regurgitation. The ECG typically shows a notched P wave in patients who are in sinus rhythm.

C. Choice of Agents

Patients may be very sensitive to the vasodilating effects of spinal and epidural anesthesia. In theory, epidural anesthesia may be easier to manage than spinal anesthesia because of the more gradual onset of sympathetic blockade. There is no “ideal” general anesthetic, and agents should be employed to achieve the desired effects of permitting sufficient diastolic time to adequately load the left ventricle. Vasopressors are often needed to maintain vascular tone following anesthetic induction.

Intraoperative tachycardia may be controlled by deepening anesthesia with an opioid (excluding meperidine) or β-blocker (esmolol or metoprolol). In the presence of atrial fibrillation, ventricular rate should be controlled. Marked hemodynamic deterioration from sudden SVT necessitates cardioversion. Phenylephrine is preferred over ephedrine as a vasopressor because the former lacks β-adrenergic agonist activity. Vasopressin can also be employed to restore vascular tone should hypotension develop secondary to anesthetic induction.

MITRAL REGURGITATION

Preoperative Considerations

Mitral regurgitation can develop acutely or insidiously as a result of a large number of disorders. Chronic mitral regurgitation is usually the result of rheumatic fever (often with concomitant mitral stenosis); congenital or developmental abnormalities of the valve apparatus; or dilation, destruction, or calcification of the mitral annulus. Acute mitral regurgitation is usually due to myocardial ischemia or infarction (papillary muscle dysfunction or rupture of a chorda tendinea), infective endocarditis, or chest trauma. The ACC/AHA indicate that primary mitral regurgitation is present when one or more of the components of the mitral valve apparatus contribute to valvular incompetence. Correction of the structure of the mitral valve corrects the underlying disease process. In contrast secondary mitral regurgitation, the ACC/AHA notes, is present when ventricular dilation prevents coaptation of the mitral valve leaflets. In this instance, repair of the valve is not curative according to the ACC/AHA’s valvular heart disease guidelines because the underlying disease process likewise must be addressed in addition to restoration of valvular competency.

Pathophysiology

The principal derangement is a reduction in forward stroke volume due to backward flow of blood into the left atrium during systole. The left ventricle compensates by dilating and increasing end-diastolic volume (Figure 21–7). Regurgitation through the mitral valve initially maintains a normal end-systolic volume in spite of an increased end-diastolic volume. However, as the disease progresses the end-systolic volume increases. By increasing end-diastolic volume, the volume-overloaded left ventricle can maintain a normal cardiac output despite blood being ejected retrograde into the atrium. With time, patients with chronic mitral regurgitation eventually develop eccentric left ventricular hypertrophy and progressive impairment in contractility. In patients with severe mitral regurgitation, the regurgitant volume may exceed the forward stroke volume. In time, wall stress increases, resulting in an increased demand for myocardial oxygen supply.

The regurgitant volume passing through the mitral valve is dependent on the size of the mitral valve orifice (which can vary with ventricular cavity size), the heart rate (systolic time), and the left ventricular–left atrial pressure gradient during systole. The last factor is affected by the relative resistances of the two outflow paths from the left ventricle, namely, SVR and left atrial compliance. Thus, a decrease in SVR or an increase in mean left atrial pressure will reduce the regurgitant volume. Atrial compliance also determines the predominant clinical manifestations. Patients with normal or reduced atrial compliance (acute mitral regurgitation) have primarily pulmonary vascular congestion and edema. Patients with increased atrial compliance (long-standing mitral regurgitation resulting in a large dilated left atrium) primarily show signs of a reduced cardiac output. Most patients are between the two extremes and exhibit symptoms of both pulmonary congestion and low cardiac output. Patients with a regurgitant fraction of less than 30% of the total stroke volume generally have mild symptoms. Regurgitant fractions of 30% to 60% generally cause moderate symptoms, whereas fractions greater than 60% are associated with severe disease.

Echocardiography, particularly TEE, is useful in delineating the underlying pathophysiology of mitral regurgitation and guiding treatment. Mitral valve leaflet motion is often described as normal, prolapsing, or restrictive (Figure 21–8). Excessive motion or prolapse is defined by systolic movement of a leaflet beyond the plane of the mitral valve and into the left atrium (see later section on mitral valve prolapse).

Treatment

Reduction of SVR increases forward stroke volume and decreases the regurgitant volume. Surgical treatment is usually reserved for patients with moderate to severe symptoms. Valvuloplasty or valve repair are performed whenever possible to avoid the problems associated with valve replacement (eg, thromboembolism, hemorrhage, and prosthetic failure). Catheter-mediated valve repairs are continually being refined, potentially reducing the need for “open” surgery. Anesthesiologists skilled in advanced perioperative echocardiography assist in correctly identifying the leaflet(s) to be repaired and determining the repair’s success. Three-dimensional echocardiography is increasingly employed to assist in the assessment of the mitral valve (see Figure 5–31).

Anesthetic Management

A. Objectives

Anesthetic management should be tailored to the severity of mitral regurgitation as well as the underlying left ventricular function. Factors that exacerbate the regurgitation, such as slow heart rates and acute increases in afterload, should be avoided. Bradycardia can increase the regurgitant volume by increasing left ventricular end-diastolic volume and acutely dilating the mitral annulus. The heart rate should ideally be kept between 80 and 100 beats/min. Acute increases in left ventricular afterload, such as with endotracheal intubation and surgical stimulation under “light” anesthesia, should be treated rapidly.

B. Monitoring

Monitors are based on the severity of ventricular dysfunction, as well as the procedure. Color-flow Doppler TEE can be invaluable in quantitating the severity of the regurgitation and guiding therapeutic interventions in patients with severe mitral regurgitation. Doppler echocardiography identifies the acceleration of blood as it is ejected through the regurgitant orifice during systole from the left ventricle into the left atrium (Figure 21–9).

C. Choice of Agents

Patients with relatively well-preserved ventricular function tend to do well with most anesthetic techniques. Spinal and epidural anesthesia are well tolerated, provided bradycardia is avoided. Patients with compromised ventricular function can likewise be managed with a variety of anesthetic agents and techniques. Invasive monitoring (arterial line, TEE) can be used to guide perioperative management in patients with severe mitral regurgitation and poor ventricular function. Inodilators such as milrinone may be employed to improve ventricular function and reduce systemic resistance in patients with poor ventricular function and severe mitral regurgitation to promote the forward as opposed to regurgitant blood flow.

MITRAL VALVE PROLAPSE

Preoperative Considerations

Mitral valve prolapse (Barlow syndrome) is classically characterized by a midsystolic click, with or without a late apical systolic murmur on auscultation. It is a relatively common abnormality that is present in up to 1% to 2.5% of the general population. The diagnosis is suggested by auscultatory findings and confirmed by echocardiography, which shows systolic prolapse of mitral valve leaflets into the left atrium. Patients with the murmur often have some element of mitral regurgitation. The posterior mitral leaflet is more commonly affected than the anterior leaflet. The mitral annulus may also be dilated. Pathologically, most patients have redundancy or some myxomatous degeneration of the valve leaflets. Most cases of mitral valve prolapse are sporadic or familial, affecting otherwise normal persons. A high incidence of mitral valve prolapse is found in patients with connective tissue disorders (particularly Marfan syndrome).

The overwhelming majority of patients with mitral valve prolapse are asymptomatic, but in a small percentage of patients, the myxomatous degeneration is progressive. Manifestations, when they occur, can include chest pains, arrhythmias, embolic events, florid mitral regurgitation, infective endocarditis, and, rarely, sudden death. The diagnosis can be made preoperatively by auscultation of the characteristic click, but must be confirmed by echocardiography. The prolapse is accentuated by maneuvers that decrease ventricular volume (preload). Both atrial and ventricular arrhythmias are common. Although bradyarrhythmias have been reported, paroxysmal supraventricular tachycardia is the most commonly encountered sustained arrhythmia. An increased incidence of abnormal AV bypass tracts is reported in patients with mitral valve prolapse.

Most patients have a normal life span. About 15% develop progressive mitral regurgitation. A smaller percentage develops embolic phenomena or infective endocarditis. Patients with both a click and a systolic murmur seem to be at greater risk of developing complications. Anticoagulation or antiplatelet agents may be used for patients with a history of emboli, whereas β-adrenergic blocking drugs are commonly used for arrhythmias.

Anesthetic Management

The management of these patients is based on their clinical course. Most patients are asymptomatic and do not require special care. Ventricular arrhythmias may occur intraoperatively, particularly following sympathetic stimulation, and will generally respond to lidocaine or β-adrenergic blocking agents. Mitral regurgitation caused by prolapse is generally exacerbated by decreases in ventricular size. Hypovolemia and factors that increase ventricular emptying or decrease afterload should be avoided. Vasopressors with pure α-adrenergic agonist activity (such as phenylephrine) may be preferable to those that are primarily β-adrenergic agonists.

AORTIC STENOSIS

Preoperative Considerations

Valvular aortic stenosis is the most common cause of obstruction to left ventricular outflow. Left ventricular outflow obstruction is less commonly due to hypertrophic cardiomyopathy, discrete congenital subvalvular stenosis, or, rarely, supravalvular stenosis. Valvular aortic stenosis is typically congenital, rheumatic, or degenerative. Abnormalities in the number of cusps (most commonly a bicuspid valve) or their architecture produce turbulence that traumatizes the valve and eventually leads to stenosis. Rheumatic aortic stenosis is rarely isolated; it is more commonly associated with aortic regurgitation or mitral valve disease. In the most common degenerative form, calcific aortic stenosis, wear and tear results in the buildup of calcium deposits on normal cusps, preventing them from opening completely (Figure 21–10).

Pathophysiology

Left ventricular outflow obstruction caused by valvular aortic stenosis is almost always gradual, allowing the ventricle, at least initially, to compensate and maintain stroke volume. Concentric left ventricular hypertrophy enables the ventricle to maintain stroke volume by generating the needed transvalvular pressure gradient and reducing ventricular wall stress.

Critical aortic stenosis is said to exist when the aortic valve orifice is reduced to 0.5 to 0.7 cm² (normal is 2.5–3.5 cm²). With this degree of stenosis, patients generally have a transvalvular gradient of approximately 50 mm Hg at rest (with a normal cardiac output) and are unable to increase cardiac output in response to exertion. Moreover, further increases in the transvalvular gradient do not significantly increase stroke volume. With long-standing aortic stenosis, myocardial contractility progressively deteriorates, compromising left ventricular function.

Classically, patients with advanced (end-stage) aortic stenosis have the triad of heart failure, angina, and syncope. Initial diagnosis in the modern era is usually made earlier in the course of the disease when the more typical complaints are exercise-induced dyspnea, vertigo, or angina. A prominent feature of aortic stenosis is a decrease in left ventricular compliance as a result of hypertrophy. Diastolic dysfunction as a result of an increase in ventricular muscle mass, fibrosis, or myocardial ischemia is to be expected. In contrast to left ventricular end-diastolic volume, which remains normal until very late in the disease, left ventricular end-diastolic pressure is elevated early in the disease. The decreased diastolic pressure gradient between the left atrium and left ventricle impairs ventricular filling, which becomes quite dependent on a normal atrial contraction. Loss of atrial systole can precipitate congestive heart failure or hypotension in patients with aortic stenosis. Cardiac output may be normal in symptomatic patients at rest, but characteristically, it does not appropriately increase with exertion. Patients may experience angina even in the absence of CAD. Myocardial oxygen demand increases because of ventricular hypertrophy, whereas myocardial oxygen supply decreases as a result of the marked compression of intramyocardial coronary vessels caused by high intracavitary systolic pressures (up to 300 mm Hg). Exertional syncope or near-syncope is thought to be due to an inability to tolerate the vasodilation in muscle tissue during exertion. Arrhythmias leading to severe hypoperfusion may also account for syncope and sudden death in some patients.

Treatment

Once symptoms develop, most patients without valve replacement will die within a few years. Percutaneous balloon valvuloplasty is generally used in younger patients with congenital aortic stenosis; it can also be used in elderly patients with calcific aortic stenosis who are poor candidates for aortic valve replacement. Its efficacy for the latter group is short-lived, however, and restenosis usually occurs within 6 to 12 months. Catheter-delivered aortic valves are increasingly being perfected and deployed in the treatment of aortic valve disease. Surgical replacement of the stenotic aortic valve remains the mainstay of therapy.

Anesthetic Management

A. Objectives

Maintenance of normal sinus rhythm, heart rate, vascular resistance, and intravascular volume is critical in patients with aortic stenosis. Loss of a normally timed atrial systole often leads to rapid deterioration, particularly when associated with tachycardia. The combination of the two (AF with rapid ventricular response) seriously impairs ventricular filling and necessitates immediate cardioversion. Fortunately, AF is uncommon in patients with aortic stenosis. The reduced ventricular compliance also makes the patient very sensitive to abrupt changes in intravascular volume. Many patients behave as though they have a fixed stroke volume in spite of adequate hydration; under these conditions, cardiac output becomes very rate dependent. Extreme bradycardia (<50 beats/min) is therefore poorly tolerated. Heart rates between 60 and 90 beats/min are optimal in most patients.

B. Monitoring

Monitoring for ischemia is complicated by baseline ST-segment and T-wave abnormalities often seen in the aortic stenosis patient. Intraarterial pressure monitoring is desirable in patients with severe aortic stenosis, as many of these patients do not tolerate even brief episodes of hypotension. Vasodilators should be used cautiously, if at all, because patients are often very sensitive to these agents. TEE can be useful in these patients for monitoring ischemia, ventricular preload, contractility, valvular function, and the effects of therapeutic interventions.

C. Choice of Agents

Patients with mild to moderate aortic stenosis (generally asymptomatic) may tolerate spinal or epidural anesthesia. These techniques should be employed very cautiously, however, because hypotension readily occurs as a result of reductions in preload, afterload, or both. A vasoconstrictor medication must be immediately available. Epidural anesthesia may be preferable to single-shot spinal anesthesia because of its slower onset of hypotension, which allows more timely correction. Continuous spinal catheters can similarly be used to gradually increase the level of block and slow the onset of hypotension.

In the patient with severe aortic stenosis the choice of anesthetic agents and techniques is less important than effective management of their hemodynamic effects. Most general anesthetics can produce both vasodilation and hypotension, which require treatment postinduction. If a volatile agent is used, the concentration should be controlled to avoid excessive vasodilation, myocardial depression, or loss of normal atrial systole. Significant tachycardia and severe hypertension, which can precipitate ischemia, should be treated immediately by increasing anesthetic depth or administration of a β-adrenergic blocking agent. Most patients with aortic stenosis tolerate moderate hypertension and are sensitive to vasodilators. Use of vasoconstrictors (eg, vasopressin, phenylephrine, norepinephrine) is often necessary to preserve systemic blood pressure in the anesthetized aortic stenosis patient. Moreover, because of an already precarious myocardial oxygen demand–supply balance, aortic stenosis patients tolerate even mild degrees of hypotension poorly. Intraoperative SVTs with hemodynamic compromise should be treated with immediate synchronized cardioversion. Frequent ventricular ectopy (which often reflects ischemia) is usually poorly tolerated hemodynamically and should be treated.

AORTIC REGURGITATION

Preoperative Considerations

Aortic regurgitation usually develops slowly and is progressive (chronic), but it can also develop quickly (acute). Chronic aortic regurgitation may be caused by abnormalities of the aortic valve, the aortic root, or both. Abnormalities in the valve are usually congenital (bicuspid valve) or due to rheumatic fever. Diseases affecting the ascending aorta cause regurgitation by dilating the aortic annulus; they include syphilis, annuloaortic ectasia, cystic medial necrosis (with or without Marfan syndrome), ankylosing spondylitis, rheumatoid and psoriatic arthritis, and a variety of other connective tissue disorders. Acute aortic insufficiency most commonly follows infective endocarditis, trauma, or aortic dissection.

Pathophysiology

Regardless of the cause, aortic regurgitation produces volume overload of the left ventricle. The effective forward stroke volume is reduced because of backward (regurgitant) flow of blood into the left ventricle during diastole. Systemic arterial diastolic pressure and SVR are typically low. The decrease in cardiac afterload helps facilitate ventricular ejection. Total stroke volume is the sum of the effective stroke volume and the regurgitant volume. The regurgitant volume depends on the heart rate (diastolic time) and the diastolic pressure gradient across the aortic valve (diastolic aortic pressure minus left ventricular end-diastolic pressure). Slow heart rates increase regurgitation because of the associated disproportionate increase in diastolic time, whereas increases in diastolic arterial pressure favor regurgitant volume by increasing the pressure gradient for backward flow.

With chronic aortic regurgitation, the left ventricle progressively dilates and undergoes eccentric hypertrophy. Patients with severe aortic regurgitation have the largest end-diastolic volumes of any heart disease. The resulting increase in end-diastolic volume maintains an effective stroke volume. Any increase in the regurgitant volume is compensated by an increase in end-diastolic volume. Left ventricular end-diastolic pressure is usually normal or only slightly elevated, because ventricular compliance initially increases. Eventually, as ventricular function deteriorates, the ejection fraction declines, and impaired ventricular emptying is manifested as gradual increases in left ventricular end-diastolic pressure and end-systolic volume.

Sudden incompetence of the aortic valve does not allow compensatory dilation or hypertrophy of the left ventricle. Effective stroke volume rapidly declines because the normal-sized ventricle is unable to accommodate a sudden large regurgitant volume. The sudden rise in left ventricular end-diastolic pressure is transmitted back to the pulmonary circulation and causes acute pulmonary venous congestion.

Acute aortic regurgitation typically presents as the sudden onset of pulmonary edema and hypotension, whereas chronic regurgitation ultimately manifests as congestive heart failure. Symptoms are generally nil or minimal in the chronic form when the regurgitant volume remains under 40% of stroke volume, but become severe when it exceeds 60%. Angina can occur even in the absence of coronary disease. The myocardial oxygen demand is increased from muscle hypertrophy and dilation; the myocardial blood supply is reduced by low diastolic pressures in the aorta as a result of the regurgitation, and peak myocardial blood flow occurs in systole rather than diastole.

Treatment

Most patients with chronic aortic regurgitation remain asymptomatic for 10 to 20 years. Once significant symptoms develop, the expected survival time is about 5 years without valve replacement. Diuretics and afterload reduction, particularly with ACE inhibitors, generally benefit patients with advanced chronic aortic regurgitation. The decrease in arterial blood pressure reduces the diastolic gradient for regurgitation. Patients with chronic aortic regurgitation should receive valve replacement before irreversible ventricular dysfunction occurs. Percutaneous aortic valve replacement is increasingly used for high-risk patients with aortic insufficiency.

Patients with acute aortic regurgitation typically require intravenous inotropic and vasodilator therapy. Early intervention is indicated in patients with acute aortic regurgitation; medical management alone is associated with a high mortality rate.

Anesthetic Management

A. Objectives

The heart rate should be maintained toward the upper limits of normal (80–100 beats/min). Bradycardia and increases in SVR increase the regurgitant volume in patients with aortic regurgitation, whereas tachycardia can contribute to myocardial ischemia. Excessive myocardial depression should also be avoided. The compensatory increase in cardiac preload should be maintained, but overzealous fluid replacement can readily result in pulmonary edema.

B. Monitoring

Invasive hemodynamic monitoring should be employed in patients with acute aortic regurgitation or those with severe chronic regurgitation. Premature closure of the mitral valve often occurs during acute aortic regurgitation and may cause pulmonary capillary wedge pressure to give a falsely high estimate of left ventricular end-diastolic pressure. The arterial pressure wave in patients with aortic regurgitation characteristically has a very wide pulse pressure. Pulsus bisferiens may also be present in patients with moderate to severe aortic insufficiency and is thought to result from the rapid ejection of a large stroke volume. Color-flow Doppler TEE can be invaluable in quantitating the severity of the regurgitation and guiding therapeutic interventions (Figure 21–11).

Severe aortic regurgitation rapidly raises left ventricular pressure during diastole. Echocardiography can also detect reversal of blood flow in the aorta during diastole in patients with severe aortic regurgitation. The more severe the regurgitation, the further distal in the aorta that diastolic flow reversal is identified.

C. Choice of Agents

Most patients with aortic insufficiency tolerate spinal and epidural anesthesia well, provided intravascular volume is maintained. When general anesthesia is required, inhalational agents may be ideal because of the associated vasodilation. Phenylephrine (25–50 mcg) can be used to treat hypotension secondary to excessive anesthetic-induced vasodilatation; however, large doses of phenylephrine may increase SVR (and arterial diastolic pressure) sufficiently to worsen the regurgitation.

TRICUSPID REGURGITATION

Preoperative Considerations

Most patients have trace to mild tricuspid regurgitation on echocardiography; the regurgitant volume in these cases is almost always trivial. Clinically significant tricuspid regurgitation, however, is most commonly due to dilation of the right ventricle from pulmonary hypertension that is associated with chronic left ventricular failure. Tricuspid regurgitation can also follow infective endocarditis, rheumatic fever, carcinoid syndrome, or chest trauma or may be due to Ebstein anomaly (downward displacement of the valve because of abnormal attachment of the valve leaflets).

Pathophysiology

Chronic left ventricular failure often leads to sustained increases in pulmonary vascular pressures. The chronic increase in afterload causes progressive dilation of the thin-walled right ventricle, and excessive dilation of the tricuspid annulus eventually results in regurgitation. An increase in end-diastolic volume allows the right ventricle to compensate for the regurgitant volume and maintain an effective forward flow. Because the right atrium and the vena cava are compliant and can usually accommodate the volume overload, mean right atrial and central venous pressures are generally only slightly elevated. Acute or marked elevations in pulmonary artery pressures increase the regurgitant volume and are reflected by an increase in central venous pressure. Moreover, sudden marked increases in right ventricular afterload sharply reduce the effective right ventricular output, reduce left ventricular preload, and can precipitate systemic hypotension.

Chronic venous hypertension leads to passive congestion of the liver and progressive hepatic dysfunction. Severe right ventricular failure with underloading of the left heart may also produce right-to-left shunting through a patent foramen ovale, which can result in marked hypoxemia.

The normal right ventricle does not extend to the apex of the heart when visualized using echocardiography. As the right heart dilates, it acquires a more spherical shape, the right ventricle extends to the apex of the heart, and the interventricular septum is flattened. These changes can impair left heart function.

Treatment

Tricuspid regurgitation is generally well tolerated by most patients. Because the underlying disorder is generally more important than the tricuspid regurgitation itself, treatment is aimed at the underlying disease process. Recent studies suggest that correction of significant tricuspid regurgitation with annuloplasty is beneficial when patients with moderate to severe tricuspid regurgitation are brought to surgery for replacement of another valve.

Anesthetic Management

A. Objectives

Hemodynamic goals should be directed primarily toward the underlying disorder. Hypovolemia and factors that increase right ventricular afterload, such as hypoxia and acidosis, should be avoided to maintain effective right ventricular stroke volume and left ventricular preload. Positive end-expiratory pressure and high mean airway pressures may also be undesirable during mechanical ventilation because they reduce venous return and increase right ventricular afterload.

B. Monitoring

Invasive monitoring may be useful. Pulmonary artery catheterization is rarely used and often not feasible; rarely a large regurgitant flow may make passage of a pulmonary artery catheter across the tricuspid valve difficult. Increasing central venous pressure implies worsening right ventricular dysfunction. The x descent is absent, and a prominent cv wave is usually present on the central venous pressure waveform. Thermodilution cardiac output measurements are falsely elevated because of the tricuspid regurgitation. Color-flow Doppler TEE is useful in evaluating the severity of the regurgitation and other associated abnormalities.

C. Choice of Agents

The selection of anesthetic agents should be based on the underlying disorder. Most patients tolerate spinal and epidural anesthesia well. Coagulopathy secondary to hepatic dysfunction should be excluded prior to any regional technique.

ENDOCARDITIS PROPHYLAXIS

The ACC/AHA guidelines regarding prophylactic antibiotic regimens in patients with prosthetic heart valves and other structural heart abnormalities have dramatically changed in recent years, decreasing the number of indications for antibiotic administration. The risk of antibiotic administration is often considered greater than the potential for developing perioperative endocarditis. At present, the ACC/AHA guidelines suggest the use of endocarditis prophylaxis in the highest risk patients undergoing dental procedures involving gingival manipulation or perforation of the oral mucosa (class IIa); see Table 21–14. Such conditions include:

• Patients with prosthetic cardiac valves or prosthetic heart materials

• Patients with a past history of endocarditis

• Patients with congenital heart disease that is either partially repaired or unrepaired

• Patients with congenital heart disease with residual defects following repair

• Patients with congenital heart disease within 6 months of a complete repair, whether catheter-based or surgical

• Cardiac transplant patients with structurally abnormal valves

Class III recommendations indicate that prophylaxis is not necessary for nondental procedures, including TEE and esophagogastroduodenoscopy, except in the presence of an active infection.

Endocarditis is believed to occur in areas of cardiac endothelial damage, where in cases of bacteremia, bacteria can be deposited and multiply. Areas of increased myocardial blood flow velocity lead to damaged endothelium, providing a template for bacterial adherence and growth. Guidelines are ever changing, and not considered to be “standard of care.” Nevertheless, deviation from guidelines often requires explanation as being outside of “evidence-based” practice. Review of the ACC/AHA guidelines is recommended when high-risk patients are encountered.

ANTICOAGULATION

Patients with mechanical prosthetic heart valves require anticoagulation, which is currently accomplished with warfarin. Aspirin is also indicated in this population, as well as in patients with bioprosthetic valves, to prevent thrombus formation. Warfarin is sometimes also used initially for mitral bioprosthetic valves.

Patients with prosthetic valves often present for noncardiac surgery that will require temporary discontinuation of anticoagulation. The ACC/AHA guidelines indicate that patients at low risk of thrombosis, such as those with bileaflet mechanical valves in the aortic position with no additional problems (eg, no AF or no hypercoagulable state) can discontinue warfarin 48 to 72 hours preoperatively so that the INR falls below 1.5. In patients at greater risk of thrombosis, warfarin should be discontinued and heparin, either unfractionated or low molecular weight, started when the INR falls below 2.0. Heparin can be discontinued 4 to 6 hours prior to surgery and then restarted as soon as surgical bleeding permits, until the patient can be restarted on warfarin therapy. Fresh frozen plasma or prothrombin complex concentrates may be given, if needed, in an emergency situation to interrupt warfarin therapy. Anesthesia providers should always consult with the patient’s surgeon and the physician responsible for prescribing the anticoagulation before adjusting anticoagulation or antiplatelet regimens perioperatively.

Preoperative Considerations

Congenital heart disease encompasses a seemingly endless list of abnormalities that may be detected in infancy, early childhood, or, less commonly, adulthood. The incidence of congenital heart disease in all live births approaches 1%. The natural history of some defects is such that patients often survive to adulthood (Table 21–15). Moreover, the number of surviving adults with corrected or palliated congenital heart disease is steadily increasing with advances in surgical and medical treatment. Patients with congenital heart disease may therefore be encountered during noncardiac surgery and obstetric deliveries. Knowledge of the anatomy of the original heart structure defect and of any corrective repairs is essential prior to anesthetizing the patient with congenital heart disease.

The complex nature and varying pathophysiology of congenital heart defects make classification difficult. A commonly used scheme is presented in Table 21–16. Most patients present with cyanosis, congestive heart failure, or an asymptomatic abnormality. Cyanosis is typically the result of an abnormal intracardiac communication that allows unoxygenated blood to reach the systemic arterial circulation (right-to-left shunting). Congestive heart failure is most prominent with defects that either obstruct left ventricular outflow or markedly increase pulmonary blood flow. The latter is usually due to an abnormal intracardiac communication that returns oxygenated blood to the right heart (left-to-right shunting). Whereas right-to-left shunts generally decrease pulmonary blood flow, some complex lesions increase pulmonary blood flow—even in the presence of right-to-left shunting. In many cases, more than one lesion is present. Survival prior to surgical correction with some anomalies (eg, transposition, total anomalous venous return, pulmonary atresia) depends on the simultaneous presence of another shunting lesion (eg, patent ductus arteriosus, patent foramen ovale, ventricular septal defect). Chronic hypoxemia in patients with cyanotic heart disease typically results in erythrocytosis. This increase in red cell mass, which is due to increased erythropoietin secretion from the kidneys, serves to restore tissue oxygen concentration to normal. Unfortunately, blood viscosity can also rise to the point at which it may interfere with oxygen delivery. When tissue oxygenation is restored to normal, the hematocrit is stable (usually <65%), and symptoms of the hyperviscosity syndrome are absent, the patient is said to have compensated erythrocytosis. Patients with uncompensated erythrocytosis do not establish this equilibrium; they have symptoms of hyperviscosity and may be at risk of thrombotic complications, particularly stroke. The risk of stroke is aggravated by dehydration. Children younger than age 4 years seem to be at greatest risk of stroke. Phlebotomy is generally not recommended if symptoms of hyperviscosity are absent and the hematocrit is less than 65%.

Coagulation abnormalities are common in patients with cyanotic heart disease. Platelet counts tend to be low-normal, and many patients have defects in the coagulation cascade. Hyperuricemia often occurs because of increased urate reabsorption secondary to renal hypoperfusion, and can result in progressively impaired kidney function.

Preoperative echocardiography is invaluable in defining the anatomy of the defect(s) and to confirm or exclude the existence of other lesions or complications, their physiological significance, and the effects of any therapeutic interventions.

Anesthetic Management

This population of patients includes four groups: (1) those who have undergone corrective cardiac surgery and require no further operations, (2) those who have had only palliative surgery, (3) those who have not yet undergone any cardiac surgery, and (4) those whose conditions are inoperable and may be awaiting cardiac transplantation. Although the management of the first group of patients may be the same as that of normal patients (except for consideration of prophylactic antibiotic therapy), the care of others requires familiarity with the complex pathophysiology of these defects (Tables 21–17 and 21–18).

For the purpose of anesthetic management, congenital heart defects may be divided into obstructive lesions, predominantly left-to-right shunts, or predominantly right-to-left shunts. Shunts can also be bidirectional and may reverse under certain conditions.

1. Obstructive Lesions

Pulmonic Stenosis

Pulmonary valve stenosis obstructs right ventricular outflow and causes concentric right ventricular hypertrophy. Severe obstruction presents in the neonatal period, whereas lesser degrees of obstruction may go undetected until adulthood. The valve is usually deformed and is either bicuspid or tricuspid. Valve leaflets are often partially fused and display systolic doming on echocardiography. The right ventricle undergoes hypertrophy, and poststenotic dilation of the pulmonary artery is often present. Symptoms are those of right ventricular heart failure. Symptomatic patients readily develop fatigue, dyspnea, and peripheral cyanosis with exertion as a result of the limited pulmonary blood flow and increased oxygen extraction by tissues. With severe stenosis, the pulmonic valve gradient exceeds 60 to 80 mm Hg, depending on the age of the patient. Right-to-left shunting may also occur in the presence of a patent foramen ovale or atrial septal defect. Cardiac output is very dependent on an elevated heart rate, but excessive increases in the latter can compromise ventricular filling. Percutaneous balloon valvuloplasty is generally considered the initial treatment of choice in most patients with symptomatic pulmonic stenosis. Anesthetic management for patients undergoing surgery should maintain a normal or slightly high heart rate, augment preload, and avoid factors that increase PVR (such as hypoxemia or hypercarbia).

2. Predominantly Left-to-Right (Simple) Shunts

Simple shunts are isolated abnormal communications between the right and left sides of the heart. Because pressures are normally higher on the left side of the heart, blood usually flows across from left to right, and blood flow through the right heart and the lungs increases. Depending on the size and location of the communication, the right ventricle may also be subjected to the higher left-sided pressures, resulting in both pressure and volume overload. Right ventricular afterload is normally 5% that of the left ventricle, so even small left-to-right pressure gradients can produce large increases in pulmonary blood flow. The ratio of pulmonary (Qp) to systemic (Qs) blood flow is useful to determine the directionality of the shunt.

A ratio greater than 1 usually indicates a left-to-right shunt, whereas a ratio less than 1 indicates a right-to-left shunt. A ratio of 1 indicates either no shunting or a bidirectional shunt of opposing magnitudes.

Large increases in pulmonary blood flow produce pulmonary vascular congestion and increase extravascular lung water. The latter interferes with gas exchange, decreases lung compliance, and increases the work of breathing. Left atrial distention also compresses the left bronchus, whereas distention of pulmonary vessels compresses smaller bronchi.

Over the course of several years, chronic increases in pulmonary blood flow produce vascular changes that irreversibly increase PVR. Elevation of right ventricular afterload produces hypertrophy and progressively raises right-sided cardiac pressures. With advanced disease, the pressures within the right heart can exceed those within the left heart. Under these conditions, the intracardiac shunt reverses and becomes a right-to-left shunt (Eisenmenger syndrome).

When a communication is small, shunt flow depends primarily on the size of the communication (restrictive shunt). When the communication is large (nonrestrictive shunt), shunt flow depends on the relative balance between PVR and SVR. An increase in SVR relative to PVR favors left-to-right shunting, whereas an increase in PVR relative to SVR favors right-to-left shunting. Common chamber lesions (eg, single atrium, single ventricle, truncus arteriosus) represent the extreme form of nonrestrictive shunts; shunt flow with these lesions is bidirectional and totally dependent on relative changes in the ventricular afterload.

The presence of shunt flow between the right and left hearts, regardless of the direction of blood flow, mandates the meticulous exclusion of air bubbles and particulate material from intravenous fluids to prevent paradoxical embolism into the cerebral or coronary circulations.

Atrial Septal Defects

Ostium secundum atrial septal defects (ASDs) are the most common form and usually occur as isolated lesions in the area of the fossa ovalis. The defect is sometimes associated with partial anomalous pulmonary venous return, most commonly of the right upper pulmonary vein. A secundum ASD may result in single or multiple (fenestrated) openings between the atria. The less common sinus venosus and ostium primum ASDs are typically associated with other cardiac abnormalities. Sinus venosus defects are located in the upper interatrial septum close to the superior vena cava; one or more of the right pulmonary veins often abnormally drains into the superior vena cava. In contrast, ostium primum ASDs are located in the lower interatrial septum and overlie the mitral and tricuspid valves; most patients also have a cleft in the anterior leaflet of the mitral valve, and some have an abnormal septal leaflet in the tricuspid valve.

Most children with ASDs are minimally symptomatic; some have recurrent pulmonary infections. Congestive heart failure and pulmonary hypertension are more commonly encountered in adults with ASDs. Patients with ostium primum defects often have large shunts and may also develop significant mitral regurgitation. In the absence of heart failure, anesthetic responses to inhalation and intravenous agents are generally not significantly altered in patients with ASDs. Large increases in SVR should be avoided because they may worsen the left-to-right shunting.

Ventricular Septal Defects

Ventricular septal defect (VSD) is a common congenital heart defect, accounting for up to 25% to 35% of congenital heart disease. The defect is most frequently found in the membranous part of the interventricular septum (membranous or infracristal VSD) in a posterior position and anterior to the septal leaflet of the tricuspid valve. Muscular VSDs are the next most frequent type and are located in the mid or apical portion of the interventricular septum, where there may be a single defect or multiple openings (resembling Swiss cheese). Defects in the subpulmonary (supracristal) septum are often associated with aortic regurgitation because the right coronary cusp can prolapse into the VSD. Septal defects at the ventricular inlet are usually similar in development and location to AV septal defects (see the following section).

The resulting functional abnormality of a VSD is dependent on the size of the defect, PVR, and the presence or absence of other abnormalities. Small VSDs, particularly of the muscular type, may close during childhood. Restrictive defects are associated with only small left-to-right shunts. Patients with small VSDs are treated medically and followed with electrocardiography (for signs of right ventricular hypertrophy) and echocardiography. Surgical closure is usually undertaken in patients with large VSDs before pulmonary vascular disease and Eisenmenger physiology develop. In the absence of heart failure, anesthetic responses to inhalation and intravenous agents are generally not significantly altered. Similarly, increases in SVR worsen the left-to-right shunting. When right-to-left shunting is present, abrupt increases in PVR or decreases in SVR are poorly tolerated.

Atrioventricular Septal Defects

Endocardial cushion (AV canal) defects produce contiguous atrial and ventricular septal defects, often with very abnormal AV valves. This is a common lesion in patients with Down syndrome. The defect can produce large shunts both at the atrial and ventricular levels. Mitral and tricuspid regurgitation exacerbate the volume overload on the ventricles. Initially, shunting is predominately left to right; however, with increasing pulmonary hypertension, Eisenmenger syndrome with obvious cyanosis develops.

Patent Ductus Arteriosus

Persistence of the communication between the main pulmonary artery and the aorta can produce restrictive or nonrestrictive left-to-right shunts. This abnormality is commonly responsible for the cardiopulmonary deterioration of premature infants and occasionally presents later in life when it can be corrected thoracoscopically. Anesthetic goals should be similar to atrial and ventricular septal defects.

Partial Anomalous Venous Return

This defect is present when one or more pulmonary veins drains into the right side of the heart; the anomalous veins are usually from the right lung. Possible anomalous entry sites include the right atrium, the superior or inferior vena cava, and the coronary sinus. The resulting abnormality produces a variable amount of left-to-right shunting. The clinical course and prognosis are usually excellent and similar to that of a secundum ASD. Obstructed total anomalous pulmonary venous return is emergently corrected immediately after birth.

3. Predominantly Right-to-Left (Complex) Shunts

Lesions within this group (some also called mixing lesions) often produce both ventricular outflow obstruction and shunting. The obstruction favors shunt flow toward the unobstructed side. When the obstruction is relatively mild, the amount of shunting is affected by the ratio of SVR to PVR, but increasing degrees of obstruction fix the direction and magnitude of the shunt. Atresia of any one of the cardiac valves represents the extreme form of obstruction. Shunting occurs proximal to the atretic valve and is completely fixed; survival depends on another distal shunt (usually a patent ductus arteriosus [PDA], patent foramen ovale, ASD, or VSD), where blood flows in the opposite direction. This group of defects may also be divided according to whether they increase or decrease pulmonary blood flow.

Tetralogy of Fallot

This anomaly classically includes right ventricular outflow obstruction, right ventricular hypertrophy, and a VSD with an overriding aorta. Right ventricular obstruction in most patients is due to infundibular stenosis, which is due to hypertrophy of the subpulmonic muscle (crista ventricularis). At least 20% to 25% of patients also have pulmonic stenosis, and a small percentage of patients has some element of supravalvular obstruction. The pulmonic valve is often bicuspid, or, less commonly, atretic. Infundibular obstruction may be increased by sympathetic tone and is therefore dynamic; this obstruction is likely responsible for the hypercyanotic spells observed in very young patients. The combination of right ventricular outflow obstruction and a VSD results in ejection of unoxygenated right ventricular blood, as well as oxygenated left ventricular blood into the aorta. The right-to-left shunting across the VSD has both fixed and variable components. The fixed component is determined by the severity of the right ventricular obstruction, whereas the variable component depends on SVR and PVR.

Surgical palliation with a left-to-right systemic shunt or complete correction is usually undertaken. For the former, a modified Blalock–Thomas–Taussig (systemic–pulmonary artery) shunt is most often used to increase pulmonary blood flow. In this procedure, a synthetic graft is anastomosed between a subclavian artery and an ipsilateral pulmonary artery. Complete correction involves closure of the VSD, removal of obstructing infundibular muscle, and pulmonic valvulotomy or valvuloplasty, when necessary.

The goals of anesthetic management in patients with tetralogy of Fallot should be to maintain intravascular volume and SVR. Increases in PVR, such as might occur from acidosis or excessive airway pressures, should be avoided. Ketamine (intramuscular or intravenous) is a commonly used induction agent because it maintains or increases SVR and therefore does not aggravate the right-to-left shunting. Patients with milder degrees of shunting generally tolerate inhalation induction. The right-to-left shunting tends to slow the uptake of inhalation anesthetics; in contrast, it may accelerate the onset of intravenous agents. Oxygenation often improves following induction of anesthesia. Muscle relaxants that release histamine should be avoided. Hypercyanotic spells may be treated with intravenous fluid and phenylephrine (5 mcg/kg). β-Blockers (eg, propranolol) may also be effective in relieving infundibular spasm.

Tricuspid Atresia

With tricuspid atresia, blood can flow out of the right atrium only via a patent foramen ovale (or an ASD). Moreover, a PDA (or VSD) is necessary for blood to flow from the left ventricle into the pulmonary circulation. Cyanosis is usually evident at birth, and its severity depends on the amount of pulmonary blood flow that is achieved. Early survival is dependent on prostaglandin E₁ infusion (to maintain PDA patency), with or without a percutaneous balloon atrial septostomy. Severe cyanosis requires a modified Blalock–Thomas–Taussig shunt early in life. The preferred surgical management is a modified Fontan procedure, in which the venous drainage is directed to the pulmonary circulation. In some centers, a superior vena cava to the main pulmonary artery (bidirectional Glenn) shunt may be employed before or instead of a Fontan procedure. With both procedures, blood from the systemic veins flows through the pulmonary circulation to the left atrium without the assistance of the right ventricle. Success of the procedure depends on a high systemic venous pressure and maintaining both low PVR and a low left atrial pressure. Heart transplantation may be necessary for a failed Fontan procedure.

Transposition of the Great Arteries

In patients with transposition of the great arteries, pulmonary and systemic venous return flows normally back to the right and left atrium, respectively, but the aorta arises from the right ventricle, and the pulmonary artery arises from the left ventricle. Thus, deoxygenated blood returns back into the systemic circulation, and oxygenated blood returns back to the lungs. Survival is possible only through mixing of oxygenated and deoxygenated blood across the foramen ovale and a PDA. The presence of a VSD increases mixing and reduces the level of hypoxemia. Prostaglandin E₁ infusion is usually necessary. Corrective surgical treatment involves an arterial switch procedure in which the aorta is divided and reanastomosed to the left ventricle, and the pulmonary artery is divided and reanastomosed to the right ventricle. The coronary arteries must also be reimplanted into the old pulmonary artery root. A VSD, if present, is closed. Less commonly, an atrial switch (Senning) procedure may be carried out if an arterial switch is not possible. In this latter procedure, an intraatrial baffle is created from the atrial wall, and blood from the pulmonary veins flows across an ASD to the right ventricle, from which it is ejected into the systemic circulation.

Transposition of the great vessels may occur with a VSD and pulmonic stenosis. This combination of defects mimics tetralogy of Fallot; however, the obstruction affects the left ventricle, not the right ventricle. Corrective surgery involves patch closure of the VSD, directing left ventricular outflow into the aorta, ligation of the proximal pulmonary artery, and connecting the right ventricular outflow to the pulmonary artery with a valved conduit (Rastelli procedure).

Truncus Arteriosus

With a truncus arteriosus defect, a single arterial trunk supplies the pulmonary and systemic circulation. Both ventricles eject into the truncus as it always overrides a VSD. As PVR gradually decreases after birth, pulmonary blood flow increases greatly, resulting in heart failure. If left untreated, PVR increases, and cyanosis develops again, along with Eisenmenger physiology. Surgical correction closes the VSD, separates the pulmonary artery from the truncus, and connects the right ventricle to the pulmonary artery with a conduit (Rastelli repair).

Hypoplastic Left Heart Syndrome

This syndrome describes a group of defects characterized by aortic valve atresia and marked underdevelopment of the left ventricle. The right ventricle is the main pumping chamber for both systemic and pulmonary circulations. It ejects normally into the pulmonary artery, and all (or nearly all) blood flow entering the aorta is usually derived from a PDA. Surgical treatment includes both the Norwood repair and a hybrid approach to palliation. In the Norwood repair, a new aorta is created from the hypoplastic aorta and the main pulmonary artery. Pulmonary blood flow is delivered via a Blalock–Thomas–Taussig shunt. The right ventricle becomes the heart’s systemic pumping ventricle. A hybrid approach has also been advocated for the palliation of hypoplastic left heart syndrome. In this approach, the pulmonary arteries are banded to reduce pulmonary blood flow, and the PDA is stented to provide for systemic blood flow.

Preoperative Considerations

The number of patients with cardiac transplants is increasing because of both the increasing frequency of transplantation and improved posttransplant survival rates. These patients may present to the operating room early in the postoperative period for mediastinal exploration or retransplantation, or they may appear later for incision and drainage of infections, orthopedic surgery, or unrelated procedures.

The transplanted heart is totally denervated, so direct autonomic influences are absent. Cardiac impulse formation and conduction are normal, but the absence of vagal influences causes a relatively high resting heart rate (100–120 beats/min). Although sympathetic fibers are similarly interrupted, the response to circulating catecholamines is normal or even enhanced because of denervation sensitivity (increased receptor density). Cardiac output tends to be low-normal and increases relatively slowly in response to exercise because the response is dependent on an increase in circulating catecholamines. Because the Starling relationship between end-diastolic volume and cardiac output is normal, the transplanted heart is also often said to be preload dependent. Coronary autoregulation is preserved.

Preoperative evaluation should focus on evaluating the functional status of the transplanted organ and detecting complications of immunosuppression. Rejection may be heralded by arrhythmias (in the first 6 months) or decreased exercise tolerance from a progressive deterioration of myocardial performance. Periodic echocardiographic evaluations are commonly used to monitor for rejection, but the most reliable technique is endomyocardial biopsy. Accelerated atherosclerosis in the graft is a very common and serious problem that limits the life of the transplant. Moreover, myocardial ischemia and infarction are almost always silent because of the denervation. Because of this, patients must undergo periodic evaluations, including angiography, for assessment of coronary atherosclerosis.

Immunosuppressive therapy may include cyclosporine, tacrolimus, and prednisone. Important side effects include nephrotoxicity, bone marrow suppression, hepatotoxicity, opportunistic infections, and osteoporosis. Hypertension and fluid retention are common and typically require treatment with a diuretic and an ACE inhibitor.

Anesthetic Management

Almost all anesthetic techniques, including regional anesthesia, have been used successfully for transplanted patients. The preload-dependent function of the graft makes maintenance of a normal or high cardiac preload desirable. Moreover, the absence of reflex increases in heart rate can make patients particularly sensitive to rapid vasodilation. Indirect vasopressors, such as ephedrine, are less effective than direct-acting agents because of the absence of catecholamine stores in myocardial neurons. Isoproterenol or epinephrine infusions should be readily available to increase the heart rate if necessary.

Electrocardiographic monitoring for ischemia is necessary. The ECG usually demonstrates two sets of P waves, one representing the recipient’s own sinoatrial (SA) node (which is left intact), and the other representing the donor’s SA node. The recipient’s SA node may still be affected by autonomic influences, but it does not affect cardiac function. Direct arterial pressure monitoring should be used for major operations; strict asepsis should be observed during placement.

In a recently transplanted patient, the right ventricle of the transplanted heart may not be able to overcome the resistance of the pulmonary vasculature. Right ventricular failure can occur perioperatively, requiring the use of inhaled nitric oxide, inotropes, and, at times, right ventricular assist devices.

Because the number of transplantable hearts is limited, patients are increasingly treated with left ventricular assist devices (LVADs). LVADs drain blood from the apex of the left ventricular and in a nonpulsatile manner pump oxygenated blood into the aorta, restoring blood delivery to the tissues (Figure 21–12). Patients require anticoagulation to prevent pump thrombosis. Maintenance of right heart function is essential to adequately supply the left side of the heart with sufficient blood for the device to eject. Hypovolemia, pulmonary hypertension, and right heart failure can lead to inadequate loading of the left heart, resulting in reduced LVAD pump flows. LVAD patients presenting for noncardiac procedures are routinely managed by cardiac anesthesiologists familiar with LVAD operations and skilled in advanced perioperative echocardiography.