Basic Mechanisms of Heart Failure
LV remodeling develops in response to a series of complex events that occur at the cellular and molecular levels (Table 234-3). These changes include (1) myocyte hypertrophy, (2) alterations in the contractile properties of the myocyte, (3) progressive loss of myocytes through necrosis, apoptosis, and autophagic cell death, (4) β-adrenergic desensitization, (5) abnormal myocardial energetics and metabolism, and (6) reorganization of the extracellular matrix with dissolution of the organized structural collagen weave surrounding myocytes and subsequent replacement by an interstitial collagen matrix that does not provide structural support to the myocytes. The biologic stimuli for these profound changes include mechanical stretch of the myocyte, circulating neurohormones (e.g., norepinephrine, angiotensin II), inflammatory cytokines [e.g., tumor necrosis factor (TNF)], other peptides and growth factors (e.g., endothelin), and reactive oxygen species (e.g., superoxide). The sustained overexpression of these biologically active molecules is believed to contribute to the progression of HF by virtue of the deleterious effects they exert on the heart and the circulation. Indeed, this insight forms the clinical rationale for using pharmacologic agents that antagonize these systems [e.g., angiotensin-converting enzyme (ACE) inhibitors and beta blockers] in treating patients with HF.
Table 234-3 Overview of Left Ventricular Remodeling
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Table 234-3 Overview of Left Ventricular Remodeling
|Alterations in Myocyte Biology|
|Myosin heavy chain (fetal) gene expression|
|Alterations in extracellular matrix|
|Alterations in Left Ventricular Chamber Geometry|
|Left ventricular (LV) dilation|
|Increased LV sphericity|
|LV wall thinning|
|Mitral valve incompetence|
In order to understand how the changes that occur in the failing cardiac myocyte contribute to depressed LV systolic function in HF, it is instructive first to review the biology of the cardiac muscle cell (Chap. 224). Sustained neurohormonal activation and mechanical overload result in transcriptional and posttranscriptional changes in the genes and proteins that regulate excitation-contraction coupling and cross-bridge interaction (see Figs. 224-6 and 224-7). The changes that regulate excitation-contraction include decreased function of sarcoplasmic reticulum Ca2+ adenosine triphosphatase (SERCA2A), resulting in decreased calcium uptake into the sarcoplamsic reticulum (SR), and hyperphosphorylation of the ryanodine receptor, leading to calcium leakage from the SR. The changes that occur in the cross-bridges include decreased expression of α-myosin heavy chain and increased expression of β-myosin heavy chain, myocytolysis, and disruption of the cytoskeletal links between the sarcomeres and the extracellular matrix. Collectively, these changes impair the ability of the myocyte to contract and therefore contribute to the depressed LV systolic function observed in patients with HF.
Myocardial relaxation is an adenosine triphosphate (ATP)-dependent process that is regulated by uptake of cytoplasmic calcium into the SR by SERCA2A and extrusion of calcium by sarcolemmal pumps (see Fig. 224-7). Accordingly, reductions in ATP concentration, as occurs in ischemia, may interfere with these processes and lead to slowed myocardial relaxation. Alternatively, if LV filling is delayed because LV compliance is reduced (e.g., from hypertrophy or fibrosis), LV filling pressures will similarly remain elevated at end diastole (see Fig. 224-11). An increase in heart rate disproportionately shortens the time for diastolic filling, which may lead to elevated LV filling pressures, particularly in noncompliant ventricles. Elevated LV end-diastolic filling pressures result in increases in pulmonary capillary pressures, which can contribute to the dyspnea experienced by patients with diastolic dysfunction. In addition to impaired myocardial relaxation, increased myocardial stiffness secondary to cardiac hypertrophy and increased myocardial collagen content may contribute to diastolic failure. Importantly, diastolic dysfunction can occur alone or in combination with systolic dysfunction in patients with HF.
Left Ventricular Remodeling
Ventricular remodeling refers to the changes in LV mass, volume, and shape and the composition of the heart that occur after cardiac injury and/or abnormal hemodynamic loading conditions. LV remodeling may contribute independently to the progression of HF by virtue of the mechanical burdens that are engendered by the changes in the geometry of the remodeled LV. In addition to the increase in LV end-diastolic volume, LV wall thinning occurs as the left ventricle begins to dilate. The increase in wall thinning, along with the increase in afterload created by LV dilation, leads to a functional afterload mismatch that may contribute further to a decrease in stroke volume. Moreover, the high end-diastolic wall stress might be expected to lead to (1) hypoperfusion of the subendocardium, with resultant worsening of LV function, (2) increased oxidative stress, with the resultant activation of families of genes that are sensitive to free radical generation (e.g., TNF and interleukin 1β), and (3) sustained expression of stretch-activated genes (angiotensin II, endothelin, and TNF) and/or stretch activation of hypertrophic signaling pathways. Increasing LV dilation also results in tethering of the papillary muscles with resulting incompetence of the mitral valve apparatus and functional mitral regurgitation, which in turn leads to further hemodynamic overloading of the ventricle. Taken together, the mechanical burdens that are engendered by LV remodeling contribute to the progression of HF.
The cardinal symptoms of HF are fatigue and shortness of breath. Although fatigue traditionally has been ascribed to the low cardiac output in HF, it is likely that skeletal-muscle abnormalities and other noncardiac comorbidities (e.g., anemia) also contribute to this symptom. In the early stages of HF, dyspnea is observed only during exertion; however, as the disease progresses, dyspnea occurs with less strenuous activity, and it ultimately may occur even at rest. The origin of dyspnea in HF is probably multifactorial (Chap. 33). The most important mechanism is pulmonary congestion with accumulation of interstitial or intra-alveolar fluid, which activates juxtacapillary J receptors, which in turn stimulate the rapid, shallow breathing characteristic of cardiac dyspnea. Other factors that contribute to dyspnea on exertion include reductions in pulmonary compliance, increased airway resistance, respiratory muscle and/or diaphragm fatigue, and anemia. Dyspnea may become less frequent with the onset of right ventricular (RV) failure and tricuspid regurgitation.
Orthopnea, which is defined as dyspnea occurring in the recumbent position, is usually a later manifestation of HF than is exertional dyspnea. It results from redistribution of fluid from the splanchnic circulation and lower extremities into the central circulation during recumbency, with a resultant increase in pulmonary capillary pressure. Nocturnal cough is a common manifestation of this process and a frequently overlooked symptom of HF. Orthopnea generally is relieved by sitting upright or sleeping with additional pillows. Although orthopnea is a relatively specific symptom of HF, it may occur in patients with abdominal obesity or ascites and patients with pulmonary disease whose lung mechanics favor an upright posture.
Paroxysmal Nocturnal Dyspnea (PND)
This term refers to acute episodes of severe shortness of breath and coughing that generally occur at night and awaken the patient from sleep, usually 1–3 hours after the patient retires. PND may be manifest by coughing or wheezing, possibly because of increased pressure in the bronchial arteries leading to airway compression, along with interstitial pulmonary edema that leads to increased airway resistance. Whereas orthopnea may be relieved by sitting upright at the side of the bed with the legs in a dependent position, patients with PND often have persistent coughing and wheezing even after they have assumed the upright position. Cardiac asthma is closely related to PND, is characterized by wheezing secondary to bronchospasm, and must be differentiated from primary asthma and pulmonary causes of wheezing.
Also referred to as periodic respiration or cyclic respiration, Cheyne-Stokes respiration is present in 40% of patients with advanced HF and usually is associated with low cardiac output. Cheyne-Stokes respiration is caused by a diminished sensitivity of the respiratory center to arterial Pco2. There is an apneic phase, during which arterial Po2 falls and arterial Pco2 rises. These changes in the arterial blood gas content stimulate the depressed respiratory center, resulting in hyperventilation and hypocapnia, followed by recurrence of apnea. Cheyne-Stokes respirations may be perceived by the patient or the patient's family as severe dyspnea or as a transient cessation of breathing.
Patients with HF also may present with gastrointestinal symptoms. Anorexia, nausea, and early satiety associated with abdominal pain and fullness are common complaints and may be related to edema of the bowel wall and/or a congested liver. Congestion of the liver and stretching of its capsule may lead to right-upper-quadrant pain. Cerebral symptoms such as confusion, disorientation, and sleep and mood disturbances may be observed in patients with severe HF, particularly elderly patients with cerebral arteriosclerosis and reduced cerebral perfusion. Nocturia is common in HF and may contribute to insomnia.
A careful physical examination is always warranted in the evaluation of patients with HF. The purpose of the examination is to help determine the cause of HF as well as to assess the severity of the syndrome. Obtaining additional information about the hemodynamic profile and the response to therapy and determining the prognosis are important additional goals of the physical examination.
General Appearance and Vital Signs
In mild or moderately severe HF, the patient appears to be in no distress at rest except for feeling uncomfortable when lying flat for more than a few minutes. In more severe HF, the patient must sit upright, may have labored breathing, and may not be able to finish a sentence because of shortness of breath. Systolic blood pressure may be normal or high in early HF, but it generally is reduced in advanced HF because of severe LV dysfunction. The pulse pressure may be diminished, reflecting a reduction in stroke volume. Sinus tachycardia is a nonspecific sign caused by increased adrenergic activity. Peripheral vasoconstriction leading to cool peripheral extremities and cyanosis of the lips and nail beds is also caused by excessive adrenergic activity.
(See also Chap. 227) Examination of the jugular veins provides an estimation of right atrial pressure. The jugular venous pressure is best appreciated with the patient lying recumbent, with the head tilted at 45°. The jugular venous pressure should be quantified in centimeters of water (normal ≤8 cm) by estimating the height of the venous column of blood above the sternal angle in centimeters and then adding 5 cm. In the early stages of HF, the venous pressure may be normal at rest but may become abnormally elevated with sustained (∼1 min) pressure on the abdomen (positive abdominojugular reflux). Giant v waves indicate the presence of tricuspid regurgitation.
Pulmonary crackles (rales or crepitations) result from the transudation of fluid from the intravascular space into the alveoli. In patients with pulmonary edema, rales may be heard widely over both lung fields and may be accompanied by expiratory wheezing (cardiac asthma). When present in patients without concomitant lung disease, rales are specific for HF. Importantly, rales are frequently absent in patients with chronic HF, even when LV filling pressures are elevated, because of increased lymphatic drainage of alveolar fluid. Pleural effusions result from the elevation of pleural capillary pressure and the resulting transudation of fluid into the pleural cavities. Since the pleural veins drain into both the systemic and the pulmonary veins, pleural effusions occur most commonly with biventricular failure. Although pleural effusions are often bilateral in HF, when they are unilateral, they occur more frequently in the right pleural space.
Examination of the heart, although essential, frequently does not provide useful information about the severity of HF. If cardiomegaly is present, the point of maximal impulse (PMI) usually is displaced below the fifth intercostal space and/or lateral to the midclavicular line, and the impulse is palpable over two interspaces. Severe LV hypertrophy leads to a sustained PMI. In some patients, a third heart sound (S3) is audible and palpable at the apex. Patients with enlarged or hypertrophied right ventricles may have a sustained and prolonged left parasternal impulse extending throughout systole. An S3 (or protodiastolic gallop) is most commonly present in patients with volume overload who have tachycardia and tachypnea, and it often signifies severe hemodynamic compromise. A fourth heart sound (S4) is not a specific indicator of HF but is usually present in patients with diastolic dysfunction. The murmurs of mitral and tricuspid regurgitation are frequently present in patients with advanced HF.
Hepatomegaly is an important sign in patients with HF. When it is present, the enlarged liver is frequently tender and may pulsate during systole if tricuspid regurgitation is present. Ascites, a late sign, occurs as a consequence of increased pressure in the hepatic veins and the veins draining the peritoneum. Jaundice, also a late finding in HF, results from impairment of hepatic function secondary to hepatic congestion and hepatocellular hypoxemia and is associated with elevations of both direct and indirect bilirubin.
Peripheral edema is a cardinal manifestation of HF, but it is nonspecific and usually is absent in patients who have been treated adequately with diuretics. Peripheral edema is usually symmetric and dependent in HF and occurs predominantly in the ankles and the pretibial region in ambulatory patients. In bedridden patients, edema may be found in the sacral area (presacral edema) and the scrotum. Long-standing edema may be associated with indurated and pigmented skin.
With severe chronic HF, there may be marked weight loss and cachexia. Although the mechanism of cachexia is not entirely understood, it is probably multifactorial and includes elevation of the resting metabolic rate; anorexia, nausea, and vomiting due to congestive hepatomegaly and abdominal fullness; elevation of circulating concentrations of cytokines such as TNF; and impairment of intestinal absorption due to congestion of the intestinal veins. When present, cachexia augurs a poor overall prognosis.
The diagnosis of HF is relatively straightforward when the patient presents with classic signs and symptoms of HF; however, the signs and symptoms of HF are neither specific nor sensitive. Accordingly, the key to making the diagnosis is to have a high index of suspicion, particularly for high-risk patients. When these patients present with signs or symptoms of HF, additional laboratory testing should be performed.
Routine Laboratory Testing
Patients with new-onset HF and those with chronic HF and acute decompensation should have a complete blood count, a panel of electrolytes, blood urea nitrogen, serum creatinine, hepatic enzymes, and a urinalysis. Selected patients should have assessment for diabetes mellitus (fasting serum glucose or oral glucose tolerance test), dyslipidemia (fasting lipid panel), and thyroid abnormalities (thyroid-stimulating hormone level).
A routine 12-lead ECG is recommended. The major importance of the ECG is to assess cardiac rhythm and determine the presence of LV hypertrophy or a prior MI (presence or absence of Q waves) as well as to determine QRS width to ascertain whether the patient may benefit from resynchronization therapy (see below). A normal ECG virtually excludes LV systolic dysfunction.
A chest x-ray provides useful information about cardiac size and shape, as well as the state of the pulmonary vasculature, and may identify noncardiac causes of the patient's symptoms. Although patients with acute HF have evidence of pulmonary hypertension, interstitial edema, and/or pulmonary edema, the majority of patients with chronic HF do not. The absence of these findings in patients with chronic HF reflects the increased capacity of the lymphatics to remove interstitial and/or pulmonary fluid.
Assessment of Lv Function
Noninvasive cardiac imaging (Chap. 229) is essential for the diagnosis, evaluation, and management of HF. The most useful test is the two-dimensional (2-D) echocardiogram/Doppler, which can provide a semiquantitative assessment of LV size and function as well as the presence or absence of valvular and/or regional wall motion abnormalities (indicative of a prior MI). The presence of left atrial dilation and LV hypertrophy, together with abnormalities of LV diastolic filling provided by pulse-wave and tissue Doppler, is useful for the assessment of HF with a preserved EF. The 2-D echocardiogram/Doppler is also invaluable in assessing RV size and pulmonary pressures, which are critical in the evaluation and management of cor pulmonale (see below). Magnetic resonance imaging (MRI) also provides a comprehensive analysis of cardiac anatomy and function and is now the gold standard for assessing LV mass and volumes. MRI also is emerging as a useful and accurate imaging modality for evaluating patients with HF, both in terms of assessing LV structure and for determining the cause of HF (e.g., amyloidosis, ischemic cardiomyopathy, hemochromatosis).
The most useful index of LV function is the EF (stroke volume divided by end-diastolic volume). Because the EF is easy to measure by noninvasive testing and easy to conceptualize, it has gained wide acceptance among clinicians. Unfortunately, the EF has a number of limitations as a true measure of contractility, since it is influenced by alterations in afterload and/or preload. Nonetheless, with the exceptions indicated above, when the EF is normal (≥50%), systolic function is usually adequate, and when the EF is significantly depressed (<30–40%), contractility is usually depressed.
Circulating levels of natriuretic peptides are useful adjunctive tools in the diagnosis of patients with HF. Both B-type natriuretic peptide (BNP) and N-terminal pro-BNP, which are released from the failing heart, are relatively sensitive markers for the presence of HF with depressed EF; they also are elevated in HF patients with a preserved EF, albeit to a lesser degree. However, it is important to recognize that natriuretic peptide levels increase with age and renal impairment, are more elevated in women, and can be elevated in right HF from any cause. Levels can be falsely low in obese patients and may normalize in some patients after appropriate treatment. At present, serial measurements of BNP are not recommended as a guide to HF therapy. Other biomarkers, such as troponin T and I, C-reactive protein, TNF receptors, and uric acid, may be elevated in HF and provide important prognostic information. Serial measurements of one or more biomarkers ultimately may help guide therapy in HF, but they are not currently recommended for this purpose.
Treadmill or bicycle exercise testing is not routinely advocated for patients with HF, but either is useful for assessing the need for cardiac transplantation in patients with advanced HF (Chap. 235). A peak oxygen uptake (Vo2) <14 mL/kg per min is associated with a relatively poor prognosis. Patients with a Vo2<14 mL/kg per min have been shown, in general, to have better survival when transplanted than when treated medically.
HF should be viewed as a continuum that is composed of four interrelated stages. Stage A includes patients who are at high risk for developing HF but do not have structural heart disease or symptoms of HF (e.g., patients with diabetes mellitus or hypertension). Stage B includes patients who have structural heart disease but do not have symptoms of HF (e.g., patients with a previous MI and asymptomatic LV dysfunction). Stage C includes patients who have structural heart disease and have developed symptoms of HF (e.g., patients with a previous MI with dyspnea and fatigue). Stage D includes patients with refractory HF requiring special interventions (e.g., patients with refractory HF who are awaiting cardiac transplantation). In this continuum, every effort should be made to prevent HF not only by treating the preventable causes of HF (e.g., hypertension) but also by treating the patient in stages B and C with drugs that prevent disease progression (e.g., ACE inhibitors and beta blockers) and by symptomatic management of patients in stage D.
Defining an Appropriate Therapeutic Strategy for Chronic HF
Once patients have developed structural heart disease, their therapy depends on their NYHA functional classification (Table 234-2). Although this classification system is notoriously subjective and has large interobserver variability, it has withstood the test of time and continues to be widely applied to patients with HF. For patients who have developed LV systolic dysfunction but remain asymptomatic (class I), the goal should be to slow disease progression by blocking neurohormonal systems that lead to cardiac remodeling (see below). For patients who have developed symptoms (class II–IV), the primary goal should be to alleviate fluid retention, lessen disability, and reduce the risk of further disease progression and death. These goals generally require a strategy that combines diuretics (to control salt and water retention) with neurohormonal interventions (to minimize cardiac remodeling).
Management of HF with Depressed Ejection Fraction (<40%)
Clinicians should aim to screen for and treat comorbidities such as hypertension, CAD, diabetes mellitus, anemia, and sleep-disordered breathing, as these conditions tend to exacerbate HF. HF patients should be advised to stop smoking and to limit alcohol consumption to two standard drinks per day in men or one per day in women. Patients suspected of having an alcohol-induced cardiomyopathy should be urged to abstain from alcohol consumption indefinitely. Extremes of temperature and heavy physical exertion should be avoided. Certain drugs are known to make HF worse and should be avoided (Table 234-4). For example, nonsteroidal anti-inflammatory drugs, including cyclooxygenase 2 inhibitors, are not recommended in patients with chronic HF because the risk of renal failure and fluid retention is markedly increased in the presence of reduced renal function or ACE inhibitor therapy. Patients should receive immunization with influenza and pneumococcal vaccines to prevent respiratory infections. It is equally important to educate the patient and family about HF, the importance of proper diet, and the importance of compliance with the medical regimen. Supervision of outpatient care by a specially trained nurse or physician assistant and/or in specialized HF clinics has been found to be helpful, particularly in patients with advanced disease.
Table 234-4 Factors That May Precipitate Acute Decompensation in Patients With Chronic Heart Failure
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Table 234-4 Factors That May Precipitate Acute Decompensation in Patients With Chronic Heart Failure
|Arrhythmias (tachycardia or bradycardia)|
|Discontinuation of HF therapy|
|Initiation of medications that worsen HF|
|Calcium antagonists (verapamil, diltiazem)|
|Nonsteroidal anti-inflammatory drugs|
|Antiarrhythmic agents [all class I agents, sotalol (class III)]|
|Acute valvular insufficiency|
Although heavy physical labor is not recommended in HF, routine modest exercise has been shown to be beneficial in patients with NYHA class I–III HF. For euvolemic patients, regular isotonic exercise such as walking or riding a stationary-bicycle ergometer, as tolerated, should be encouraged. Exercise training results in reduced HF symptoms, increased exercise capacity, and improved quality of life.
Dietary restriction of sodium (2–3 g daily) is recommended in all patients with HF and preserved or depressed EF. Further restriction (<2 g daily) may be considered in moderate to severe HF. Fluid restriction is generally unnecessary unless the patient develops hyponatremia (<130 meq/L), which may develop because of activation of the renin-angiotensin system, excessive secretion of antidiuretic hormone, or loss of salt in excess of water from diuretic use. Fluid restriction (<2 L/day) should be considered in hyponatremic patients or those whose fluid retention is difficult to control despite high doses of diuretics and sodium restriction. Vasopressin antagonists also may be useful in severe hyponatremia. Caloric supplementation is recommended for patients with advanced HF and unintentional weight loss or muscle wasting (cardiac cachexia); however, anabolic steroids are not recommended for these patients because of the potential problems with volume retention. The use of dietary supplements (“nutriceuticals”) should be avoided in the management of symptomatic HF because of the lack of proven benefit and the potential for significant (adverse) interactions with proven HF therapies.
Many of the clinical manifestations of moderate to severe HF result from excessive salt and water retention that leads to volume expansion and congestive symptoms. Diuretics (Table 234-5) are the only pharmacologic agents that can adequately control fluid retention in advanced HF, and they should be used to restore and maintain normal volume status in patients with congestive symptoms (dyspnea, orthopnea, edema) or signs of elevated filling pressures (rales, jugular venous distention, peripheral edema). Furosemide, torsemide, and bumetanide act at the loop of Henle (loop diuretics) by reversibly inhibiting the reabsorption of Na+, K+, and Cl− in the thick ascending limb of Henle's loop; thiazides and metolazone reduce the reabsorption of Na+ and Cl− in the first half of the distal convoluted tubule; and potassium-sparing diuretics such as spironolactone act at the level of the collecting duct.
Table 234-5 Drugs for the Treatment of Chronic Heart Failure (EF <40%)
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Table 234-5 Drugs for the Treatment of Chronic Heart Failure (EF <40%)
|Initiating Dose||Maximal Dose|
|Furosemide||20–40 mg qd or bid||400 mg/da|
|Torsemide||10–20 mg qd bid||200 mg/da|
|Bumetanide||0.5–1 mg qd or bid||10 mg/da|
|Hydrochlorthiazide||25 mg qd||100 mg/da|
|Metolazone||2.5–5 mg qd or bid||20 mg/da|
|Angiotensin-Converting Enzyme Inhibitors|
|Captopril||l6.25 mg tid||50 mg tid|
|Enalapril||2.5 mg bid||10 mg bid|
|Lisinopril||2.5–5 mg qd||20–35 mg qd|
|Ramipril||1.25–2.5 mg bid||2.5–5 mg bid|
|Trandolapri||0.5 mg qd||4 mg qd|
|Angiotensin Receptor Blockers|
|Valsartan||40 mg bid||160 mg bid|
|Candesartan||4 mg qd||32 mg qd|
|Irbesartan||75 mg qd||300 mg qdb|
|Losartan||12.5 mg qd||50 mg qd|
|β Receptor Blockers|
|Carvedilol||3.125 mg bid||25–50 mg bid|
|Bisoprolol||1.25 mg qd||10 mg qd|
|Metoprolol succinate CR||12.5–25 mg qd||Target dose 200 mg qd|
|Spironolactone||12.5–25 mg qd||25–50 mg qd|
|Eplerenone||25 mg qd||50 mg qd|
|Combination of hydralazine/isosorbide dinitrate||10–25 mg/10 mg tid||75 mg/40 mg tid|
|Fixed dose of hydralazine/isosorbide dinitrate||37.5 mg/20 mg (one tablet) tid||75 mg/40 mg (two tablets) tid|
|Digoxin||0.125 mg qd||≤0.375 mg/db|
Although all diuretics increase sodium excretion and urinary volume, they differ in their potency and pharmacologic properties. Whereas loop diuretics increase the fractional excretion of sodium by 20–25%, thiazide diuretics increase it by only 5–10% and tend to lose their effectiveness in patients with moderate or severe renal insufficiency (creatinine >2.5 mg/dL). Hence, loop diuretics generally are required to restore normal volume status in patients with HF. Diuretics should be initiated in low doses (Table 234-5) and then carefully titrated upward to relieve signs and symptoms of fluid overload in an attempt to obtain the patient's “dry weight.” This typically requires multiple dose adjustments over many days and occasionally weeks in patients with severe fluid overload. Intravenous administration of diuretics may be necessary to relieve congestion acutely and can be done safely in the outpatient setting. Once the congestion has been relieved, treatment with diuretics should be continued to prevent the recurrence of salt and water retention.
Refractoriness to diuretic therapy may represent patient nonadherence, a direct effect of chronic diuretic use on the kidney, or progression of underlying HF. The addition of thiazides or metolazone, once or twice daily, to loop diuretics may be considered in patients with persistent fluid retention despite high-dose loop diuretic therapy. Metolazone is generally more potent and much longer-acting than the thiazides in this setting as well as in patients with chronic renal insufficiency. However, chronic daily use, especially of metolazone, should be avoided if possible because of the potential for electrolyte shifts and volume depletion. Ultrafiltration and dialysis may be used in cases of refractory fluid retention that are unresponsive to high doses of diuretics and have been shown to be helpful in the short term.
Diuretics have the potential to produce electrolyte and volume depletion as well as worsening azotemia. In addition, they may lead to worsening neurohormonal activation and disease progression. One of the most important adverse consequences of diuresis is alterations in potassium homeostasis (hypokalemia or hyperkalemia), which increase the risk of life-threatening arrhythmias. In general, both loop- and thiazide-type diuretics lead to hypokalemia, whereas spironolactone, eplerenone, and triamterene lead to hyperkalemia.
Preventing Disease Progression (Table 234-5)
Drugs that interfere with excessive activation of the RAA system and the adrenergic nervous system can relieve the symptoms of HF with a depressed EF by stabilizing and/or reversing cardiac remodeling. In this regard, ACE inhibitors and beta blockers have emerged as the cornerstones of modern therapy for HF with a depressed EF.
There is overwhelming evidence that ACE inhibitors should be used in symptomatic and asymptomatic patients (Figs. 234-3 and 234-4) with a depressed EF (<40%). ACE inhibitors interfere with the renin-angiotensin system by inhibiting the enzyme that is responsible for the conversion of angiotensin I to angiotensin II. However, because ACE inhibitors also inhibit kininase II, they may lead to the upregulation of bradykinin, which may further enhance the beneficial effects of angiotensin suppression. ACE inhibitors stabilize LV remodeling, improve symptoms, reduce hospitalization, and prolong life. Because fluid retention can attenuate the effects of ACE inhibitors, it is preferable to optimize the dose of diuretic before starting the ACE inhibitor. However, it may be necessary to reduce the dose of diuretic during the initiation of ACE inhibition to prevent symptomatic hypotension. ACE inhibitors should be initiated in low doses, followed by gradual increments if the lower doses have been well tolerated. The doses of ACE inhibitors should be increased until they are similar to those which have been shown to be effective in clinical trials (Table 234-5). Higher doses are more effective than lower doses in preventing hospitalization.
Meta-analysis of angiotensin-converting enzyme (ACE) inhibitors in heart failure patients with a depressed ejection fraction.
A. The Kaplan-Meier curves for mortality for 5966 HF patients with a depressed EF treated with an ACE inhibitor after acute myocardial infarction (three trials).
B. The Kaplan-Meier curves for mortality for 12,763 HF patients with a depressed EF treated with an ACE inhibitor in five clinical trials, including postinfarction trials. The benefits of ACE inhibitors were observed early and persisted long-term. (Modified from MD Flather et al: Lancet 355:1575, 2000.)
Treatment algorithm for chronic heart failure patients with a depressed ejection fraction. After the clinical diagnosis of HF is made, it is important to treat the patient's fluid retention before starting an ACE inhibitor (or an ARB if the patient is ACE-intolerant). Beta blockers should be started after the fluid retention has been treated and/or the ACE inhibitor has been uptitrated. If the patient remains symptomatic, an ARB, an aldosterone antagonist, or digoxin can be added as “triple therapy.” The fixed-dose combination of hydralazine/isosorbide dinitrate should be added to an ACE inhibitor and a beta blocker in African-American patients with NYHA class II–IV HF. Device therapy should be considered in addition to pharmacologic therapy in appropriate patients. HF, heart failure; ACE, angiotensin-converting enzyme; ARB, angiotensin receptor blocker; NYHA, New York Heart Association; CRT, cardiac resynchronization therapy; ICD, implantable cardiac defibrillator.
The majority of adverse effects are related to suppression of the renin-angiotensin system. The decreases in blood pressure and mild azotemia that may occur during the initiation of therapy generally are well tolerated and do not require a decrease in the dose of the ACE inhibitor. However, if hypotension is accompanied by dizziness or if the renal dysfunction becomes severe, it may be necessary to reduce the dose of the inhibitor. Potassium retention may also become problematic if the patient is receiving potassium supplements or a potassium-sparing diuretic. Potassium retention that is not responsive to these measures may require a reduction in the dose of ACE inhibitor.
The side effects of ACE inhibitors related to kinin potentiation include a nonproductive cough (10–15% of patients) and angioedema (1% of patients). In patients who cannot tolerate ACE inhibitors because of cough or angioedema, angiotensin receptor blockers (ARBs) are the recommended first line of therapy (see below). Patients intolerant of ACE inhibitors because of hyperkalemia or renal insufficiency are likely to experience the same side effects with ARBs. In these cases, the combination of hydralazine and an oral nitrate should be considered (Table 234-5).
Angiotensin Receptor Blockers
These drugs are well tolerated in patients who are intolerant of ACE inhibitors because of cough, skin rash, and angioedema. ARBs should be used in symptomatic and asymptomatic patients with an EF <40% who are ACE-intolerant for reasons other than hyperkalemia or renal insufficiency (Table 234-5). Although ACE inhibitors and ARBs inhibit the renin-angiotensin system, they do so by different mechanisms. Whereas ACE inhibitors block the enzyme responsible for converting angiotensin I to angiotensin II, ARBs block the effects of angiotensin II on the angiotensin type 1 receptor. Some clinical trials have demonstrated a therapeutic benefit from the addition of an ARB to an ACE inhibitor in patients with chronic HF. When given in concert with beta blockers, ARBs reverse the process of LV remodeling, improve patient symptoms, prevent hospitalization, and prolong life.
Both ACE inhibitors and ARBs have similar effects on blood pressure, renal function, and potassium. Therefore, the problems of symptomatic hypotension, azotemia, and hyperkalemia are similar for both of these agents.
β-Adrenergic Receptor Blockers
Beta-blocker therapy represents a major advance in the treatment of patients with a depressed EF (Fig. 234-5). These drugs interfere with the harmful effects of sustained activation of the adrenergic nervous system by competitively antagonizing one or more adrenergic receptors (α1, β1, and β2). Although there are a number of potential benefits to blocking all three receptors, most of the deleterious effects of adrenergic activation are mediated by the β1 receptor. When given in concert with ACE inhibitors, beta blockers reverse the process of LV remodeling, improve patient symptoms, prevent hospitalization, and prolong life. Therefore, beta blockers are indicated for patients with symptomatic or asymptomatic HF and a depressed EF <40%.
Meta-analysis of beta blockers on mortality rates in HF patients with a depressed EF. Effect of beta blockers vs. placebo in patients who were not (A) or who were (B) receiving an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin receptor blocker (ARB) at baseline in six clinical trials. There was a similar impact of beta-blocker therapy on the endpoints of all-cause mortality as well as death and heart failure hospitalization in both the presence and the absence of ACE inhibitor or ARB at baseline. BEST, Beta-Blocker Evaluation of Survival Trial (bucindolol); CIBIS, Cardiac Insufficiency Bisoprolol Study (bisoprolol); COPERNICUS, Carvedilol prOsPEctive RaNdomIzed Cumulative Survival (carvedilol); MERIT-HF, Metoprolol CR/XL Randomized Intervention Trial in Heart Failure (metoprolol CR/XL). (Modified from H Krum et al: Eur Heart J 26:2154, 2005.)
Analogous to the use of ACE inhibitors, beta blockers should be initiated in low doses (Table 234-5), followed by gradual increments in the dose if lower doses have been well tolerated. The dose of beta blocker should be increased until the doses used are similar to those which have been reported to be effective in clinical trials (Table 234-5). However, unlike ACE inhibitors, which may be titrated upward relatively rapidly, the titration of beta blockers should proceed no more rapidly than at 2-week intervals, because the initiation and/or increased dosing of these agents may lead to worsening fluid retention consequent to the withdrawal of adrenergic support to the heart and the circulation. Thus, it is important to optimize the dose of diuretic before starting therapy with beta blockers. If worsening fluid retention does occur, it is likely to do so within 3–5 days of the initiation of therapy, and it will be manifest as an increase in body weight and/or symptoms of worsening HF. The increased fluid retention usually can be managed by increasing the dose of diuretics. In some patients the dose of the beta blocker may have to be reduced.
Contrary to early reports, the aggregate results of clinical trials suggest that beta-blocker therapy is well tolerated by the great majority (≥85%) of HF patients, including patients with comorbid conditions such as diabetes mellitus, chronic obstructive lung disease, and peripheral vascular disease. Nonetheless, there is a subset of patients (10–15%) who remain intolerant to beta blockers because of worsening fluid retention or symptomatic hypotension or bradycardia.
The adverse effects of beta-blocker use generally are related to the predictable complications that arise from interfering with the adrenergic nervous system. These reactions generally occur within several days of the initiation of therapy and generally are responsive to adjustments of concomitant medications, as described above. Therapy with beta blockers can lead to bradycardia and/or exacerbate heart block. Accordingly, the dose of beta blocker should be reduced if the heart rate decreases to <50 beats/min and/or second- or third-degree heart block or symptomatic hypotension develops. Beta blockers are not recommended for patients who have asthma with active bronchospasm. Beta blockers that also block the α1 receptor can lead to vasodilatory side effects.
Although classified as potassium-sparing diuretics, drugs that block the effects of aldosterone (spironolactone or eplerenone) have beneficial effects that are independent of the effects of these agents on sodium balance. Although ACE inhibition may transiently decrease aldosterone secretion, with chronic therapy there is a rapid return of aldosterone to levels similar to those before ACE inhibition. Accordingly, the administration of an aldosterone antagonist is recommended for patients with NYHA class IV or class III (previously class IV) HF who have a depressed EF (<35%) and are receiving standard therapy, including diuretics, ACE inhibitors, and beta blockers. The dose of aldosterone antagonist should be increased until the doses used are similar to those which have been shown to be effective in clinical trials (Table 234-5).
The major problem with the use of aldosterone antagonists is the development of life-threatening hyperkalemia, which is more prone to occur in patients who are receiving potassium supplements or who have underlying renal insufficiency. Aldosterone antagonists are not recommended when the serum creatinine is >2.5 mg/dL (or creatinine clearance is <30 mL/min) or when the serum potassium is >5 mmol/L. Painful gynecomastia may develop in 10–15% of patients who use spironolactone, in which case eplerenone may be substituted.
The combination of hydralazine and isosorbide dinitrate (Table 234-5) is recommended as part of standard therapy in addition to beta blockers and ACE inhibitors for African Americans with NYHA class II–IV HF. Although the exact mechanism for the effects of this combination is not known, it is believed to be secondary to the beneficial effects of NO on the peripheral circulation.
Management of Patients WHO Remain Symptomatic
Additional pharmacologic therapy should be considered in patients who have persistent symptoms or progressive worsening despite optimized therapy with an ACE inhibitor and a beta blocker. Agents that may be considered as part of additional therapy include an ARB, spironolactone, the combination of hydralazine and isosorbide dinitrate, and digitalis. The optimal choice of additional drug therapy to improve the outcome further has not been firmly established. Thus, the choice of a specific agent will be influenced by clinical considerations, including renal function, serum potassium concentration, blood pressure, and race. The triple combination of an ACE inhibitor, an ARB, and an aldosterone antagonist should not be used because of the high risk of hyperkalemia.
Digoxin is recommended for patients with symptomatic LV systolic dysfunction who have concomitant atrial fibrillation, and it should be considered for patients who have signs or symptoms of HF while receiving standard therapy, including ACE inhibitors and beta blockers. Therapy with digoxin is commonly initiated and maintained at a dose of 0.125–0.25 mg daily. For the great majority of patients, the dose should be 0.125 mg daily, and the serum digoxin level should be <1 ng/mL, especially in elderly patients, patients with impaired renal function, and patients with a low lean body mass. Higher doses (and serum concentrations) appear to be less beneficial. There is no indication for using loading doses of digoxin to initiate therapy in patients with HF.
Anticoagulation and Antiplatelet Therapy
Patients with HF have an increased risk for arterial or venous thromboembolic events. In clinical HF trials, the rate of stroke ranges from 1.3 to 2.4% per year. Depressed LV function is believed to promote relative stasis of blood in dilated cardiac chambers with increased risk of thrombus formation. Treatment with warfarin [goal international normalized ratio (INR) 2–3] is recommended for patients with HF and chronic or paroxysmal atrial fibrillation or with a history of systemic or pulmonary emboli, including stroke or transient ischemic attack. Patients with symptomatic or asymptomatic ischemic cardiomyopathy and documented recent large anterior MI or recent MI with documented LV thrombus should be treated with warfarin (goal INR 2–3) for the initial 3 months after the MI unless there are contraindications to its use.
Aspirin is recommended in HF patients with ischemic heart disease for the prevention of MI and death. However, lower doses of aspirin (75 or 81 mg) may be preferable because of the concern of worsening of HF at higher doses.
Management of Cardiac Arrhythmias
(See also Chap. 233) Atrial fibrillation occurs in 15–30% of patients with HF and is a common cause of cardiac decompensation. Most antiarrhythmic agents, with the exception of amiodarone and dofetilide, have negative inotropic effects and are proarrhythmic. Amiodarone is a class III antiarrhythmic that has few or no negative inotropic and/or proarrhythmic effects and is effective against most supraventricular arrhythmias. Amiodarone is the preferred drug for restoring and maintaining sinus rhythm, and it may improve the success of electrical cardioversion in patients with HF. Amiodarone increases the level of phenytoin and digoxin and prolongs the INR in patients taking warfarin. Therefore, it is often necessary to reduce the dose of these drugs by as much as 50% when initiating therapy with amiodarone. The risk of adverse events such as hyperthyroidism, hypothyroidism, pulmonary fibrosis, and hepatitis is relatively low, particularly when lower doses of amiodarone are used (100–200 mg/d).
Implantable cardiac defibrillators (ICDs; see below) are highly effective in treating recurrences of sustained ventricular tachycardia and/or ventricular fibrillation in HF patients with recurrent arrhythmias and/or cardiac syncope, and they may be used as stand-alone therapy or in combination with amiodarone and/or a beta blocker (Chap. 233). There is no role for treating ventricular arrhythmias with an antiarrhythmic agent without an ICD.
Approximately one-third of patients with a depressed EF and symptomatic HF (NYHA class III–IV) manifest a QRS duration >120 ms. This ECG finding of abnormal inter- or intraventricular conduction has been used to identify patients with dyssynchronous ventricular contraction. The mechanical consequences of ventricular dyssynchrony include suboptimal ventricular filling, a reduction in LV contractility, prolonged duration (and therefore greater severity) of mitral regurgitation, and paradoxical septal wall motion. Biventricular pacing, also termed cardiac resynchronization therapy (CRT), stimulates both ventricles nearly simultaneously, thereby improving the coordination of ventricular contraction and reducing the severity of mitral regurgitation. When CRT is added to optimal medical therapy in patients in sinus rhythm, there is a significant decrease in patient mortality rates and hospitalization and a reversal of LV remodeling, as well as improved quality of life and exercise capacity. Accordingly, CRT is recommended for patients in sinus rhythm with an EF <35% and a QRS >120 ms and those who remain symptomatic (NYHA III–IV) despite optimal medical therapy. The benefits of CRT in patients with atrial fibrillation have not been clearly established.
Implantable Cardiac Defibrillators
(See also Chap. 233) The prophylactic implantation of ICDs in patients with mild to moderate HF (NYHA class II–III) has been shown to reduce the incidence of sudden cardiac death in patients with ischemic or nonischemic cardiomyopathy. Accordingly, implantation of an ICD should be considered for patients in NYHA class II–III HF with a depressed EF of <35% who are already on optimal background therapy, including an ACE inhibitor (or ARB), a beta blocker, and an aldosterone antagonist. An ICD may also be combined with a biventricular pacemaker in patients with NYHA class III–IV HF.
Management of HF with a Preserved Ejection Fraction (>40–50%)
Despite the wealth of information with respect to the evaluation and management of HF with a depressed EF, there are no proven and/or approved pharmacologic or device therapies for the management of patients with HF and a preserved EF. Therefore, it is recommended that initial treatment efforts should be focused, wherever possible, on the underlying disease process (e.g., myocardial ischemia, hypertension) associated with HF with preserved EF. Precipitating factors such as tachycardia and atrial fibrillation should be treated as quickly as possible through rate control and restoration of sinus rhythm when appropriate. Dyspnea may be treated by reducing total blood volume (dietary sodium restriction and diuretics), decreasing central blood volume (nitrates), or blunting neurohormonal activation with ACE inhibitors, ARBs, and/or beta blockers. Treatment with diuretics and nitrates should be initiated at low doses to avoid hypotension and fatigue.
Defining an Appropriate Therapeutic Strategy
The therapeutic goals for the management of acute decompensated HF (ADHF) therapy are to (1) stabilize the hemodynamic derangements that provoked the symptoms responsible for the hospitalization, (2) identify and treat the reversible factors that precipitated decompensation, and (3) reestablish an effective outpatient medical regimen that will prevent disease progression and relapse. In most instances this will require hospitalization, often in an intensive care unit (ICU) setting. Every effort should be made to identify the precipitating causes, such as infection, arrhythmias, dietary indiscretion, pulmonary embolism, infective endocarditis, occult myocardial ischemia/infarction, and environmental and/or emotional stress (Table 234-4), since removal of these precipitating events is critical to the success of treatment.
The two primary hemodynamic determinants of ADHF are elevated LV filling pressures and a depressed cardiac output. Frequently the depressed cardiac output is accompanied by an increase in systemic vascular resistance (SVR) as a result of excessive neurohormonal activation. Because these hemodynamic derangements may occur singly or together, patients with acute HF generally present with one of four basic hemodynamic profiles (Fig. 234-6): normal LV filling pressure with normal perfusion (Profile A), elevated LV filling pressure with normal perfusion (Profile B), elevated LV filling pressures with decreased perfusion (Profile C), and normal or low LV filling pressure with decreased tissue perfusion (Profile L).
Hemodynamic profiles in patients with acute heart failure. Most patients can be categorized into one of the four hemodynamic profiles by performing a brief bedside examination that includes examination of the neck veins, lungs, and peripheral extremities. More definitive hemodynamic information may be obtained by performing invasive hemodynamic monitoring, particularly if the patient is gravely ill or if the clinical presentation is unclear. This hemodynamic classification provides a useful guide for selecting the initial optimal therapies for the management of acute HF. LV, left ventricular; CO, cardiac output; SVR, systemic vascular resistance. (Modified from Grady et al: Circulation 102:2443, 2000.)
Accordingly, the therapeutic approach to treating patients with acute HF should be tailored to reflect the patient's hemodynamic presentation. The goal should be, whenever possible, to restore the patient to a normal hemodynamic profile (Profile A). In many instances the patient's hemodynamic presentation can be approximated from the clinical examination. For example, patients with elevated LV filling pressures may have signs of fluid retention (rales, elevated neck veins, peripheral edema) and are referred to as being “wet,” whereas patients with a depressed cardiac output and an elevated SVR generally have poor tissue perfusion manifested by cool distal extremities and are referred to as being “cold.” Nonetheless, it should be emphasized that patients with chronic heart failure may not have rales or evidence of peripheral edema at the time of the initial presentation with acute decompensation, and this may lead to the underrecognition of elevated filling pressures. In these patients, it may be appropriate to perform invasive hemodynamic monitoring.
Patients who are not congested and have normal tissue perfusion are referred to as being “dry” and “warm,” respectively. When acute HF patients present to the hospital with Profile A, their symptoms are often due to conditions other than HF (e.g., pulmonary or hepatic disease or transient myocardial ischemia). More commonly, however, acute HF patients present with congestive symptoms [“warm and wet” (Profile B)], in which case treatment of the elevated filling pressures with diuretics and vasodilators is warranted to reduce LV filling pressures. Profile B includes most patients with acute pulmonary edema. The treatment of this life-threatening condition is described in Chap. 272.
Patients also may present with congestion and a significantly elevated SVR and reduction of cardiac output [“cold and wet” (Profile C)]. In these patients, cardiac output can be increased and LV filling pressures reduced by using intravenous vasodilators. Intravenous inotropic agents with vasodilating action [dobutamine, low-dose dopamine, milrinone (Table 234-6)] augment cardiac output by stimulating myocardial contractility as well as by functionally unloading the heart.
Table 234-6 Drugs for the Treatment for Acute Heart Failure
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Table 234-6 Drugs for the Treatment for Acute Heart Failure
|Initiating Dose||Maximal Dose|
|Nitroglycerin||20 μg/min||40–400 μg/min|
|Nitroprusside||10 μg/min||30–350 μg/min|
|Nesiritide||Bolus 2 μg/kg||0.01–0.03 μg/kg per mina|
|Dobutamine||1–2 μg/kg per min||2–10 μg/kg per minb|
|Milrinone||Bolus 50 μg/kg||0.1–0.75 μg/kg per minb|
|Dopamine||1–2 μg/kg per min||2–4 μg/kg per minb|
|Levosimendan||Bolus 12 μg/kg||0.1–0.2 μg/kg per minc|
|Dopamine for hypotension||5 μg/kg per min||5–15 μg/kg per min|
|Epinephrine||0.5 μg/kg per min||50 μg/kg per min|
|Phenylephrine||0.3 μg/kg per min||3 μg/kg per min|
|Vasopressin||0.05 units/min||0.1–0.4 units/min|
Patients who present with Profile L (“cold and dry”) should be carefully evaluated by right-heart catheterization for the presence of an occult elevation of LV filling pressures. If LV filling pressures are low [pulmonary capillary wedge pressure (PCWP) <12 mmHg], a cautious trial of fluid repletion may be considered. The goals of further therapy depend on the clinical situation. Therapy to reach the aforementioned goals may not be possible in some patients, particularly if they have disproportionate RV dysfunction or if they develop cardiorenal syndrome, in which renal function deteriorates during aggressive diuresis. Worsening renal dysfunction occurs in approximately 25% of patients hospitalized with HF and is associated with prolonged hospital stays and higher mortality rates after discharge.
Pharmacologic Management of Acute HF
After diuretics, intravenous vasodilators are the most useful medications for the management of acute HF. By stimulating guanylyl cyclase within smooth-muscle cells, nitroglycerin, nitroprusside, and nesiritide exert dilating effects on arterial resistance and venous capacitance vessels, which results in a lowering of LV filling pressure, a reduction in mitral regurgitation, and improved forward cardiac output without increasing heart rate or causing arrhythmias. Hypotension is the most common side effect of all vasodilating agents.
Intravenous nitroglycerin generally is begun at 20 μg/min and is increased in 20-μg increments until patient symptoms are improved or PCWP is decreased to 16 mmHg without reducing systolic blood pressure below 80 mmHg. The most common side effect of IV or oral nitrates is headache, which, if mild, can be treated with analgesics and often resolves during continued therapy. Nitroprusside generally is initiated at 10 μg/min and increased by 10–20 μg every 10–20 min as tolerated, with the same hemodynamic goals as described above. The rapidity of onset and offset, with a half-life of approximately 2 min, facilitates early establishment of an individual patient's optimal level of vasodilation in the ICU. The major limitation of nitroprusside is side effects from cyanide toxicity, which manifests predominantly as gastrointestinal and central nervous system manifestations and is most likely to occur in patients receiving >250 μg/min for over 48 h.
Nesiritide, the newest vasodilator, is a recombinant form of brain-type natriuretic peptide, which is an endogenous peptide secreted primarily from the LV in response to an increase in wall stress. Nesiritide is given as a bolus (2 μg/kg) followed by a fixed-dose infusion (0.01–0.03 μg/kg per min). Nesiritide effectively lowers LV filling pressures and improves symptoms during the treatment of acute HF. Headache is less common with nesiritide than with nitroglycerin. Although termed a natriuretic peptide, nesiritide has not been associated with major diuresis when used alone in clinical trials. It does, however, appear to potentiate the effect of concomitant diuretics such that the total required diuretic dose may be slightly lower. There have, however, been recent concerns about the adverse effects of neseritide on renal function in acute decompensated HF which may be related to the initial bolus.
Positive inotropic agents produce direct hemodynamic benefits by stimulating cardiac contractility as well as by producing peripheral vasodilation. Collectively, these hemodynamic effects result in an improvement in cardiac output and a fall in LV filling pressures.
Dobutamine, which is the most commonly used inotropic agent for the treatment of acute HF, exerts its effects by stimulating β1 and β2 receptors, with little effect on α1 receptors. Dobutamine is given as a continuous infusion at an initial infusion rate of 1–2 μg/kg per min. Higher doses (>5 μg/kg per min) are frequently necessary for severe hypoperfusion; however, there is little added benefit to increasing the dose above 10 μg/kg per min. Patients maintained on chronic infusions for >72 h generally develop tachyphylaxis and require increasing doses.
Milrinone is a phosphodiesterase III inhibitor that leads to increased cyclic AMP by inhibiting its breakdown. Milrinone may act synergistically with β-adrenergic agonists to achieve a greater increase in cardiac output than is achieved with either agent alone, and it may also be more effective than dobutamine in increasing cardiac output in the presence of beta blockers. Milrinone may be administered as a bolus dose of 50 μg/kg per min, followed by a continuous infusion rate of 0.1–0.75 μg/kg per min. If the patient has a low blood pressure, many clinicians will omit the bolus dose. Because milrinone is a more effective vasodilator than dobutamine, it produces a greater reduction in LV filling pressures, albeit with a greater risk of hypotension.
Although short-term use of inotropes provides hemodynamic benefits, these agents are more prone to cause tachyarrhythmias and ischemic events than vasodilators are. Therefore, inotropes are most appropriately used in clinical settings in which vasodilators and diuretics are not helpful, such as in patients with poor systemic perfusion and/or cardiogenic shock, patients requiring short-term hemodynamic support after an MI or surgery, and patients awaiting cardiac transplantation, or as palliative care in patients with advanced HF. If patients require sustained use of intravenous inotropes, strong consideration should be given to the use of an ICD to safeguard against the proarrhythmic effects of these agents.
Vasoconstrictors are used to support systemic blood pressure in patients with HF. Of the three agents that are commonly used (Table 234-6), dopamine is generally the first choice for therapy in situations in which modest inotropy and pressor support are required. Dopamine is an endogenous catecholamine that stimulates β1 and α1 receptors and dopaminergic receptors (DA1 and DA2) in the heart and circulation. The effects of dopamine are dose-dependent. Low doses of dopamine (<2 μg/kg per min) stimulate the DA1 and DA2 receptors and cause vasodilation of the splanchnic and renal vasculature. Moderate doses (2–4 μg/kg per min) stimulate the β1 receptors and cause an increase in cardiac output with little or no change in heart rate or SVR. At higher doses (≥5 μg/kg per min) the effects of dopamine on the α1 receptors overwhelm the dopaminergic receptors, and vasoconstriction ensues, leading to an increase in SVR, LV filling pressures, and heart rate. Significant additional inotropic and blood pressure support can be provided by epinephrine, phenylephrine, and vasopressin (Table 234-6); however, prolonged use of these agents can lead to renal and hepatic failure and can cause gangrene of the limbs. Therefore, these agents should not be administered except in true emergency situations.
Vasopressin levels are often elevated in patients with HF and LV dysfunction and may contribute to the hyponatremia that develops in HF patients. Vasopressin antagonists reduce body weight and edema and normalize serum sodium in patients with hyponatremia but have not been associated with improved patient outcomes in clinical trials. Tolvaptan (oral) and conivaptan (IV) are currently approved for the treatment of hyponatremia but are not approved for the treatment of HF.
Mechanical and Surgical Interventions
If pharmacologic interventions fail to stabilize a patient with refractory HF, mechanical and surgical interventions may provide effective circulatory support. These interventions include intraaortic balloon counter pulsation, percutaneous and surgically implanted LV assist devices, and cardiac transplantation (Chap. 235).
Planning for Hospital Discharge
Patient education should take place during the entire hospitalization, with a specific focus on salt and fluid status and obtaining daily weights, in addition to medication schedules. Although the majority of patients hospitalized with HF can be stabilized and returned to a good level of function on an oral regimen designed to maintain stability, 30–50% of patients discharged with a diagnosis of HF are rehospitalized within 3–6 months. Although there are multiple reasons for rehospitalization, failure to meet criteria for discharge is perhaps the most common. Criteria for discharge should include at least 24 h of stable fluid status, blood pressure, and renal function on the oral regimen planned for home. Before discharge, patients should be free of dyspnea or symptomatic hypotension while at rest, washing, and walking on the ward.