31: Syncope

Transient loss of consciousness may be caused by trauma, intoxication, hypoglycemia, or true syncope. Syncope refers to the abrupt, transient complete loss of consciousness and postural tone due to transient global cerebral hypoperfusion, usually due to transient profound hypotension. Since such profound hypotension can be catastrophic or fatal if prolonged, syncope may portend sudden cardiac death; therefore, a careful evaluation is critical to identify and treat patients with potentially life- threatening etiologies of syncope.

Patients with syncope should be carefully evaluated to determine if they are at risk for sudden cardiac death.

The differential diagnosis for syncope is best remembered by considering the 3 most common causes of syncope: reflex mediated syncope, cardiac syncope, and orthostatic hypotension (Figure 31-1).

Each of these categories of syncope is associated with specific diseases/entities that cause syncope. Cardiac syncope is usually due to bradyarrhythmias or tachyarrhythmias but occasionally due to outflow obstruction (eg, aortic stenosis, hypertrophic cardiomyopathy [HCM]) or inadequate filling (pulmonary embolism [PE], tamponade). Orthostatic hypotension is usually due to inadequate preload (from dehydration or hemorrhage), but may also be secondary to autonomic dysfunction or drugs. Reflex syncope refers to a group of disorders that cause syncope due to increased vagal tone causing bradycardia and vasodilation and includes vasovagal syncope, carotid sinus syncope, and situational syncope. The full differential is listed below.

Finally, cerebrovascular disease involving the posterior circulation is a rare cause of transient loss of consciousness but is almost invariably associated with other neurologic symptoms and is discussed briefly at the end of the chapter. On the other hand, seizures are easily confused with syncope and remain in the differential diagnosis of the patient who appears to have had syncope (see Figure 31-1).

The evaluation of all patients with syncope must include a thorough history, physical exam, ECG, and blood glucose. A detailed history of the event is critical including the setting (warm, standing, sitting, during exertion, pain, anxiety, etc.), associated symptoms (nausea, chest pain, palpitations), and any signs observed by bystanders. Any significant persistence of confusion beyond a minute or two is critical, as this would suggest a postictal period and seizure. The past medical history and the patient’s medications should be carefully reviewed. The purpose of this evaluation is to uncover any findings that suggest cardiac disease, since patients with syncope and heart disease are at a markedly increased risk for ventricular tachycardia (VT) and sudden death. Such findings include syncope which occurs during sitting or exertion, associated symptoms of chest pain, palpitations, or dyspnea, a past medical history of heart disease (coronary artery disease [CAD], structural heart disease or heart failure [HF]), a family history of sudden cardiac death or significant murmurs, an S₃ gallop or jugular venous distention (JVD) (suggesting aortic stenosis and HF, respectively). On the other hand, syncope with prolonged standing or associated with abdominal discomfort increases the likelihood of vasovagal syncope whereas syncope immediately upon standing suggests orthostatic syncope. The physical exam should evaluate vital signs and orthostatic BPs in addition to a thorough cardiac and neurologic exam. Finally, an ECG should be obtained in every syncopal patient and scrutinized for signs of arrhythmia, conduction disease, ischemia, or structural heart disease. An echocardiogram may also be useful in patients with risk factors for heart disease but no known structural heart disease (eg, hypertension). Patients with any risk factors for cardiac syncope should be admitted for evaluation (Figure 31-2).

Differential Diagnosis of Transient Loss of Consciousness

1. Syncope

   1. Reflex syncope

      1. Vasovagal syncope

      2. Situational syncope (cough, micturition, or defecation)

      3. Carotid sinus syndrome

   2. Orthostatic syncope

      1. Inadequate left ventricular (LV) preload

         • (1) Dehydration (nausea, vomiting, diarrhea, uncontrolled diabetes, over dialysis, adrenal insufficiency)

         • (2) Hemorrhage

      2. Autonomic failure

         • (1) Primary autonomic failure: multisystem atrophy, Parkinson disease

         • (2) Secondary autonomic failure: diabetes mellitus, vitamin B₁₂ deficiency, uremia

      3. Drug (alcohol, diuretics, alpha-blockers, vasodilators, nitrates)

   3. Cardiac syncope

      1. Arrhythmias

         • (1) Tachycardias

           • (a) VT

             • (i) Secondary to structural heart disease, eg, HF, ischemic heart disease, acute myocardial infarction (MI), valvular heart disease

             • (ii) Congenital eg, long QT syndrome, Brugada syndrome

             • (iii) Electrolyte derangements or hypoxia

             • (iv) Medications (tricyclic antidepressants, antiarrhythmics, phenothiazines, macrolides, protease inhibitors, nonsedating antihistamines and diuretics (due to electrolyte abnormalities)

           • (b) Supraventricular tachycardia associated with accessory pathway (Wolff-Parkinson-White [WPW] syndrome)

         • (2) Bradycardias

           • (a) Sinus node disorders

             • (i) Sinus bradycardia (< 35 bpm)

             • (ii) Sinus pauses (> 3 seconds or > 2 seconds with symptoms)

           • (b) Atrioventricular (AV) block (second- or third-degree)

      2. Structural heart disease

         • (1) Aortic stenosis

         • (2) HCM

         • (3) Rare causes: atrial myxoma, prosthetic valve dysfunction, aortic dissection

      3. Other: Inadequate filling

         • (1) Cardiac tamponade

         • (2) Pulmonary embolism

2. Generalized seizures

3. Cerebrovascular disorders

   1. Vertebrobasilar insufficiency

   2. Subclavian steal

Mr. M’s history clearly suggests syncope rather than trauma or intoxication. His rapid recovery without intervention argues against either seizure or hypoglycemia. The setting (associated with a strong emotional trigger) and associated symptoms of nausea and warmth are classic for vasovagal syncope, a form of reflex syncope. However, as mentioned above it is critical to also consider potentially life-threatening causes of syncope that might suggest cardiac syncope. The past medical history, family history, physical exam, and ECG could provide invaluable clues to congenital heart disease or preexistent heart disease. In young patients the most common “must not miss” form of cardiac syncope is HCM. Although rare, the long QT syndrome should also be considered. Patients with the long QT syndrome may have life-threatening arrhythmias triggered by emotional stress. Table 31-1 lists the differential diagnosis.

Leading Hypothesis: Reflex Syncope due to Vasovagal Syncope

Textbook Presentation

Vasovagal syncope typically occurs in young patients while standing (either prolonged or associated with pain or anxiety ie, phlebotomy). Lightheadedness, nausea, and diaphoresis may precede syncope, which is brief.

Disease Highlights

1. Reflex syncope refers to a group of related disorders that cause syncope by triggering inappropriate cardiovascular reflexes that produce hypotension and syncope.

   1. The predominant reflex may produce bradycardia (cardioinhibitory type), or vasodilatation (vasodepressor type) or be mixed.

   2. This distinction may affect the choice of therapy, with pacemakers a potential option for patients with severe, recurrent symptomatic cardioinhibitory reflex syncope.

   3. The triggers vary with the type of reflex syncope.

      1. Vasovagal syncope: upright posture with or without stress

      2. Carotid sinus hypersensitivity (Carotid pressure, see below)

      3. Situational syncope associated with defecation, micturition, or post exercise syncope).

2. Vasovagal syncope is the most common form of reflex syncope and the most common cause of syncope (20–33% of cases).

3. Pathophysiology (Figure 31-3)

   1. Patients are often in a low preload state due to venous pooling (from prolonged standing) or dehydration.

   2. Superimposed anxiety, pain, or fear triggers a sympathetic surge, which augments ventricular contraction.

   3. Vigorous contraction coupled with low preload results in low end-systolic volume, which triggers intracardiac mechanoreceptors.

   4. The mechanoreceptors trigger the vagal reflex.

   5. Vagal reflex triggers bradycardia, vasodilatation, or both, resulting in hypotension and syncope.

Evidence-Based Diagnosis

1. History

   1. Provocative circumstances include prolonged standing (37%), hot weather (42%), lack of food (23%), fear (21%), and acute pain (14%).

   2. No single finding is very sensitive for vasovagal syncope (14–40%).

   3. However, certain findings are fairly specific and increase the likelihood of vasovagal syncope when present.

      1. Prolonged standing (LR+ 9.0)

      2. Abdominal discomfort prior to syncope (LR+ 8)

      3. Occurring during injection/cannulation (LR+ 7)

      4. Dehydration (LR+ 3.7)

      5. Nausea after syncope (LR+ 3.5)

      6. Although vasovagal syncope can occur after exercise it is rare during exercise. Syncope during exercise should raise the suspicion of cardiogenic syncope.

2. Laboratory and radiologic tests

   1. Patients with a typical history, a normal physical exam and ECG, and no evidence of heart disease or red flags do not require further testing.

   2. Patients with an atypical history (ie, without a clear precipitant) and those with heart disease or red flags require an echocardiogram and tilt-table testing.

   3. Tilt-table testing is particularly useful in patients with recurrent events in whom the diagnosis is unclear.

      1. The patient is initially supine for 20–45 minutes.

      2. The table is then tilted to 60–80 degrees and the patient kept upright for 30–45 minutes during which time the pulse and BP are continuously monitored.

      3. Criteria for a positive test include the reproduction of the presyncopal or syncopal symptoms with hypotension, bradycardia, or both.

      4. Sensitivity is 26–80% and specificity is about 90% for reflex syncope.

         • (1) Test characteristics are estimates because there is no real gold standard.

         • (2) Estimates vary depending on tilt-table angle, duration, and medications used.

         • (3) A variety of medications can increase sensitivity but may decrease specificity (eg, isoproterenol and nitrates).

      5. Determining the mechanism of syncope (cardioinhibitory vs vasodepressor)

         • (1) Tilt-table testing does not reliably predict the mechanism of syncope in patients with reflex syncope and the potential utility of pacemaker therapy.

         • (2) Compared with implantable loop recorders (ILRs) (that documents rhythm disturbances during unprovoked syncope), tilt-table testing is specific but insensitive in detecting asystole or bradycardia (sensitivity 35%, specificity 90%, LR+ 3.5, LR– 0.72).

   4. ILRs

      1. ILRs are devices implanted into the left pectoral region that can record arrhythmias during syncope for up to 36 months.

      2. Useful in patients with recurrent events that may not be captured with continuous loop event monitors and have not been reproduced using tilt table

      3. Typically reserved for patients with severe recurrent events that are not amenable to standard therapies (see below) to determine whether the mechanism of vasovagal syncope is cardioinhibitory (and potentially amenable to pacemaker therapy) or vasodepressor

      4. The diagnostic yield of ILR in undiagnosed but recurrent syncope in patients over age 40 without structural heart disease is 35% at 2 years. Importantly, 19% of such patients had severe symptomatic bradyarrhythmias (usually asystole). Another 11% of patients had no arrhythmia during syncope ruling out an arrhythmogenic cause.

   5. An approach to reflex syncope is illustrated in Figure 31-4.

Treatment

1. Patients should be reassured, instructed to avoid triggers, and lie down if they notice the premonitory signs of an impending faint.

2. Vasodilators (eg, alpha-blockers), diuretics, and alcohol should be eliminated or decreased.

3. Hand grip, arm tensing, and leg crossing in which the muscles are tensed for 2 minutes significantly raises BP and can decrease vasovagal syncope (absolute risk reduction 19%, NNT 5).

4. Midodrine is an alpha-agonist that may be useful. However, compliance is limited due to its three times daily dosing requirements.

5. Fludrocortisone and beta-blockers have not been proven effective.

6. Pacemakers are useful for select patients with severe recurrent cardioinhibitory reflex syncope refractory to other treatments. Patients ≥ 40 years old (without structural heart disease) with asystole on ILR (≥ 3 seconds with syncope or ≥ 6 seconds without syncope) have fewer recurrences with pacemaker treatment (absolute risk reduction 32%, NNT 3).

Mr. M’s well-defined precipitant for vasovagal syncope and typical premonitory symptoms combined with the absence of red flags for serious cardiac syncope (such as HF, ischemic heart disease, advanced age, abnormal physical exam or ECG) makes neurocardiogenic syncope the most likely diagnosis. His normal ECG rules out the long QT syndrome. You still wonder if you need to consider HCM.

Alternative Diagnosis: HCM

Textbook Presentation

Patients with HCM may be asymptomatic and discovered due to a family history of sudden cardiac death, during the evaluation of an asymptomatic systolic murmur, during preparticipation athletic screening, or when symptoms occur (syncope, HF, atrial fibrillation, or cardiac arrest).

Disease Highlights

1. The most common cause of cardiovascular death in young people and among young athletes

2. A large number of different autosomal dominant mutations in genes that encode sarcomere constituents result in myocyte hypertrophy with disarray, increased cardiac fibrosis, and diastolic dysfunction. Over 1400 variants in 11 genes have been reported.

3. Affects 1/500 adults in the general population

4. Left ventricular hypertrophy (LVH) in the absence of loading conditions (hypertension, aortic stenosis, etc.) is the hallmark of the disease.

   1. LVH may develop in childhood, adolescence, or adulthood.

   2. LVH can affect any part of the LV, although often preferentially affects the ventricular septum, which can cause outflow tract obstruction.

   3. Outflow tract obstruction increases the risk of progression to HF, stroke, and sudden cardiac death. The outflow obstruction can be fixed or variable.

   4. The obstruction may generate high velocities, which draw the mitral valve leaflet toward the septum (known as systolic anterior motion of the mitral valve). This further aggravates the outflow obstruction and simultaneously causes mitral regurgitation.

   5. Chamber size affects the magnitude of obstruction. A smaller chamber size (ie, from hypovolemia) brings the anterior leaflet of mitral valve closer to the hypertrophied septum and increases obstruction. This occurs when preload decreases (such as with standing), or when afterload decreases or contractility increases.

5. Most patients are asymptomatic or mildly symptomatic.

6. Complications include HF, angina, mitral regurgitation, atrial fibrillation, stroke, syncope, and sudden cardiac death.

   1. HF

      1. More common in patients with outflow obstruction

      2. Develops due to a combination of outflow obstruction and diastolic dysfunction

      3. Dyspnea on exertion is the most common symptom.

      4. Aggravated by concomitant mitral regurgitation when present

      5. Systolic dysfunction is unusual but may also develop.

   2. Angina

      1. May be typical or atypical in quality

      2. Develops in 25–30% of patients

      3. Ischemia is not primarily due to epicardial CAD, but results from a mismatch of oxygen supply and demand.

      4. Aggravated by massive LVH and abnormal microvasculature

      5. Concomitant CAD may be present.

   3. Syncope

      1. Develops in 15–25% of patients with HCM

      2. May be due to ventricular arrhythmias, outflow tract obstruction, ischemia and, rarely, conduction blocks

   4. Sudden cardiac death is the most dreaded complication.

      1. Often occurs in previously asymptomatic patients

      2. Secondary to ventricular tachyarrhythmias (which may be triggered by myocardial fibrosis and disarray, outflow tract obstruction, or ischemia)

      3. Annual risk among all patients with HCM: 0.6–1%

      4. Major risk factors include the following:

         • (1) Prior events

           • (a) Prior cardiac arrest

           • (b) Spontaneous sustained VT

         • (2) High-risk clinical factors

           • (a) Family history of sudden cardiac death in first-degree relative

           • (b) Unexplained syncope (particularly if repetitive, exercise-induced, or occurs in children)

           • (c) Massive LVH (≥ 30 mm)

         • (3) Other risk factors

           • (a) Abnormal BP response to exercise

           • (b) Nonsustained VT on Holter monitoring ≥ 3 beats at ≥ 120 bpm

         • (4) Of note electrophysiologic (EP) studies are not recommended for routine risk stratification of sudden cardiac death.

      5. Atrial fibrillation

         1. Left atrial enlargement may develop secondary to decreased LV compliance or mitral regurgitation and creates a substrate for the development of atrial fibrillation.

         2. Atrial fibrillation decreases LV filling and worsens the outflow tract obstruction.

      6. Stroke is usually secondary to concomitant atrial fibrillation and subsequent embolization.

7. Annual evaluation

   1. History and physical exam

   2. Family history

   3. Echocardiography

   4. 48-hour Holter monitoring (to look for nonsustained VT)

   5. Exercise stress testing (to assess BP response to exercise and evaluate ischemia)

Evidence-Based Diagnosis

1. The classic murmur of HCM is a harsh systolic murmur heard at the apex and lower left sternal border.

   1. It is accentuated by maneuvers that decrease chamber size (resulting in an increased obstruction).

   2. The murmur increases as a patient goes from a squatting to a standing position (sensitivity 95%, specificity 84%; LR+ 5.9, LR− 0.06).

   3. Passive leg elevation decreases the murmur (sensitivity 85% specificity 91%; LR+ 9.4, LR− 0.16).

2. ECG findings

   1. ECG abnormalities may precede echocardiographic abnormalities and may increase in frequency with age.

   2. Abnormalities include repolarization changes (ST segment elevation, depression or T wave inversions) and voltage criteria for LVH. Other findings may include prominent Q waves, left atrial enlargement, and left axis deviation.

   3. Abnormal in 86–90% of affected patients with echocardiographic LVH and 46% of affected patients (gene positive) without LVH.

   4. Voltage criteria for LVH are present in 65% of patients with echocardiographic LVH and 32% of gene-positive patients without echocardiographic LVH.

3. Echocardiogram

   1. May be normal until adolescence of later in life

   2. Criteria for HCM include LV wall thickening (≥ 15 mm) in the absence of other conditions known to cause LVH (ie, hypertension or aortic stenosis).

      1. LVH can occur in any part of the LV and in an array of distributions but is often asymmetric in distribution.

      2. The classic pattern that has specific consequences is marked septal hypertrophy.

4. Cardiac MR can be used when echocardiography is suboptimal.

5. DNA analysis

   1. DNA analysis can identify mutant genes but remains imprecise.

   2. Less than 50% of affected patients have an identifiable mutation and many mutations are of uncertain significance.

   3. Testing relatives of patients with HCM can be useful, especially when probands have a known pathogenic mutation. Testing can both identify affected relatives before the development of LVH and can also rule out the disease.

Treatment

1. Evaluation

   1. Initial laboratory tests should include a 12-lead ECG, transthoracic echocardiography, Holter monitor and continuous loop event monitor (for patients with palpitations or light headedness).

   2. Annual evaluation should include 12-lead ECG, echocardiogram and Holter monitoring.

   3. Exercise transthoracic echocardiography can be used to evaluate dynamic obstruction in patients with a resting dynamic outflow obstruction of < 50 mm Hg.

2. Medical therapy

   1. Asymptomatic patients

      1. Patients should avoid dehydration and strenuous exertion. Low intensity aerobic exercise is reasonable.

      2. Beta-blockers and calcium channel blockers are unproven in asymptomatic HCM with or without obstruction.

      3. Vasodilators and high-dose diuretics should be avoided in patients with HCM and obstruction.

      4. Septal reduction should not be performed in asymptomatic patients.

   2. Symptomatic patients

      1. Beta-blockers

         • (1) Decrease contractility and slow HR, augmenting diastolic filling and thereby decreasing dynamic outflow obstruction

         • (2) Recommended in patients with dyspnea or angina

      2. Verapamil

         • (1) Can be used if beta-blockers are ineffective or not tolerated

         • (2) Should not be used concurrently with beta-blockers due to a high frequency of heart block and HF associated with their combined use.

         • (3) Other contraindications include advanced HF, high gradients, or sinus bradycardia.

      3. Disopyramide has also been used.

      4. Diuretics can be used if dyspnea persists despite treatment with beta-blockers or verapamil.

      5. Many drugs are contraindicated (dihydropyridines, digoxin, positive inotropes, and others).

3. Surgery

   1. Septal reduction surgery can reduce LV outflow tract obstruction. Indications are complex but include drug refractory symptoms (chest pain, dyspnea, syncope or near syncope) in patients with significant (≥ 50 mm Hg) LV outflow tract obstruction.

   2. Alcohol septal ablation can induce septal infarction and is another option.

      1. However, compared with surgical myomectomy, there appears to be an increased risk of subsequent life-threatening arrhythmias, heart block, complications, and less reliable symptom relief.

      2. Reserved for nonsurgical candidates.

4. Implantable cardiac defibrillator (ICD)

   1. ICDs are the most effective strategy to prevent sudden cardiac death in patients with HCM.

   2. Recommended for high-risk HCM patients. The ACCF/AHA recommends an ICD for HCM patients with a history of a prior cardiac arrest, spontaneous sustained VT, a family history of sudden cardiac death in first-degree relative, massive LVH, or unexplained syncope.

   3. Some studies also suggest that an abnormal BP response to exercise (in patients’ ≤ 40 years old), nonsustained VT, and gadolinium enhancement on cardiac MR also confer an increased risk of sudden cardiac death.

5. Screening

   1. First-degree relatives of affected patients should be screened for the specific mutation (if it is known).

   2. If the relative’s screening results are normal, no further testing is required. If results are abnormal (or if the mutation is unknown), an ECG, transthoracic echocardiography, and clinical evaluation should be performed every 12–18 months in children and adolescents and every 5 years in adults.

   3. Preparticipation screening with a history (including family history), physical exam, and ECG of all young competitive athletes has been demonstrated to reduce the incidence of sudden cardiac death by 79% primarily due to a reduction in deaths from HCM.

As noted above, Mr. M’s history and physical exam and normal ECG suggest vasovagal syncope. There is no family history of sudden cardiac death, significant murmur, or ECG abnormality to suggest either the long QT syndrome or HCM. There is no history of dehydration or offending medications (eg, vasodilators). Tilt-table testing is not indicated in patients with isolated episodes of well-defined vasovagal syncope.

As illustrated in Figure 31-1 the first step in patients with loss of consciousness is to determine whether this was due to syncope, trauma, intoxication, hypoglycemia, or seizure. The patient was not intoxicated and did not experience any trauma. The spontaneous rapid recovery essentially rules out seizure and hypoglycemia (further substantiated by the normal blood glucose at the time). Thus, the history clearly suggests syncope. The second pivotal step in such patients is to determine whether the patient has cardiac syncope, orthostatic hypotension, or reflex syncope. As illustrated in Figure 31-2, this process is driven by a search for risk factors to determine whether the patient is at risk for cardiac syncope, which could be life-threatening. In particular, patients should be asked about a prior history of heart disease; syncope precipitated with exertion or while supine; and any associated chest pain, dyspnea, or palpitations.

Mr. C’s does not have exertional syncope, chest pain, palpitations, or dyspnea at the time of syncope. Nonetheless, his history of MIs substantially increases the likelihood of cardiac syncope, which becomes both the leading hypothesis and a must not miss hypothesis. Furthermore, his history of dyspnea on minimal exertion, JVD, and S₃ gallop all suggest HF. HF in turn markedly increases the likelihood of VT as a cause of cardiac syncope. Although he lacks chest pain, his prior history of CAD and MI increase the likelihood of syncope associated with an acute coronary syndrome, another must not miss hypothesis. Orthostatic syncope (secondary to dehydration, hemorrhage, or drugs) is unlikely given his lack of postural BP change with standing. Although hypoglycemia should be considered in diabetic patients taking insulin, sulfonylureas, or thiazolidinediones, it is essentially ruled out by the rapid recovery without intervention and documented normoglycemia at the time of syncope. Hypoglycemia-induced syncope is usually preceded by either confusion or sympathetic stimulation producing tremulousness, nervousness, or diaphoresis. Another “must not miss” alternative includes PE, which is an uncommon cause of syncope. Vasovagal syncope is unlikely because Mr. C.’s syncope occurred while sitting and was not preceded by any pain or anxiety. Table 31-2 lists the differential diagnosis.

Leading Hypothesis: Cardiac Syncope

Textbook Presentation

Cardiac syncope refers to syncope secondary to a disorder arising within the heart. Arrhythmias (either tachyarrhythmias or bradyarrhythmias) are the most common disorders. Less common disorders include acute coronary syndromes, severe valvular heart disease (eg, aortic stenosis), and PE. Rare causes include aortic dissection, cardiac tamponade, and atrial myxoma. Classically, patients with cardiac syncope are elderly patients with known heart disease (ie, HF or CAD) who experience sudden syncope, which may occur without warning. Patients may have palpitations.

Disease Highlights

1. Cardiac syncope is associated with increased mortality.

   1. The 1-year mortality rate in patients with cardiac syncope is 18–33%, compared with 6% in patients with syncope of unknown cause.

   2. Preexistent heart disease increases the likelihood of cardiac syncope.

   3. Subsequent mortality in syncopal patients increases with the severity of heart disease.

      1. Class 1–2 HF, OR 7.7

      2. Class 3–4 HF, OR 13.5

   4. Among patients with dilated cardiomyopathy, sudden cardiac death (presumably arrhythmogenic) accounts for 30% of the mortality.

   5. Patients in whom cardiac syncope is suspected should be admitted for evaluation.

2. Although there are a large number of cardiac dysrhythmias, only a relative few produce syncope. Most supraventricular tachyarrhythmias will not cause syncope because the AV node limits the ventricular response rate. The most common arrhythmias associated with syncope include

   1. Tachycardias

      1. VT

      2. Supraventricular tachycardias associated with an accessory pathway (ie, WPW syndrome [see end of chapter]).

   2. Bradycardias

      1. Sinus node dysfunction

         • (1) Sinus bradycardia (< 35 bpm)

         • (2) Sinus pauses (defined as > 3 seconds or > 2 seconds with symptoms)

      2. AV heart block (second- or third-degree)

      3. Atrial fibrillation with a slow ventricular response

Evidence-Based Diagnosis

1. History

   1. Certain clinical findings are uncommon but substantially increase the likelihood of cardiac syncope when present including syncope associated with chest pain, syncope during exertion (LR+ 6.5–14), or syncope when supine (LR+ 4.0–∞).

      Syncope during exertion is unusual but worrisome and may suggest CAD, HCM, long QT syndrome, polymorphic VT, and WPW.

   2. Other symptoms may suggest cardiac syncope but are less specific (palpitations, syncope of sudden onset, dyspnea associated with syncope).

   3. Cardiac syncope is unlikely in patients without known or suspected cardiac disease on the basis of the initial history, physical exam, and ECG (LR 0.09–0.12).

   4. Table 31-3 summarizes the sensitivity, specificity, and LR for symptoms in predicting cardiac syncope.

2. ECG

   1. An abnormal ECG increases the OR of cardiac arrhythmias in patients without vasovagal syncope (OR, 23.5 [CI, 7 – 87]).

   2. Certain ECG findings in syncopal patients may suggest particular cardiac etiologies.

      1. ECG evidence of prior MI or a long QT interval increases the likelihood of VT.

      2. ECG findings of significant bradycardia, second- or third-degree AV block increase the likelihood of syncope due to sick sinus syndrome (SSS) or AV block.

      3. Bundle branch block (BBB) on ECG increases the likelihood of both AV block and VT.

         • (1) Mortality in syncopal patients with BBB is 28% at 40 months. 32% of the deaths were sudden death.

         • (2) The increased mortality is attributed to a combination of VT or electromechanical dissociation in patients with underlying heart disease.

         • (3) AV block develops in 17% of patients with BBB and syncope.

         • (4) EP studies can document prolonged conduction through the His-Purkinje system and is highly specific but insensitive (67%). ILR recordings can also be useful.

         • (5) Pacemaker therapy effectively prevents syncope in almost all such patients (but does not prevent sudden death).

      4. Right ventricular strain (S1Q3T3) or right BBB suggests PE.

      5. Ischemic changes suggest MI.

      6. Delta wave or short PR interval suggests an accessory pathway (eg, WPW syndrome).

3. Clinical decision rules have been developed that combine the clinical risk factors and ECG to predict cardiac syncope and 2-year total mortality.

   1. One such score is the EGSYS score (see Table 31-4).

   2. A score of ≥ 3 predicted cardiac syncope (92% sensitive, 69% specific, LR+ 3, LR− 0.12).

   3. Syncope while supine is uncommon and under-represented in studies. Patients with a score of 2 due to syncope while supine should be evaluated for cardiac syncope.

4. Other tests

   1. Echocardiograms

      1. Rarely diagnostic of arrhythmia but useful for risk stratification because VT is much more common in presence of LV dysfunction.

      2. Used to assess LV function and valve function (eg, aortic stenosis)

      3. Should be obtained in patients with a history of CAD, HF, valvular disease, significant clinical findings (S₃ gallop, JVD, significant murmurs) or patients with risk factors for heart disease (eg, hypertension).

   2. Exercise testing

      1. Particularly useful in patients with exertional syncope or chest pain

      2. Also obtained in patients with cardiac disease, ischemic changes on ECG

      3. May be useful in patients with dyspnea on exertion

   3. Holter monitoring: External cardiac leads are applied to the patient and a 24- to 48-hour recording of the cardiac rhythm is made.

      1. Diagnostic only if

         • (1) Arrhythmia captured and patient symptomatic during arrhythmia or

         • (2) Rhythm normal during symptoms (excludes an arrhythmia)

      2. Often nondiagnostic due to

         • (1) Absence of arrhythmia during study

         • (2) Absence of symptoms during arrhythmia

   4. External loop recorders

      1. External devices that can be worn for up to 1 month. A continuous recording is made.

      2. If symptoms occur, most recent 2–5 minutes can be frozen in memory and transmitted by telephone.

      3. Relative short duration of monitoring (1 month) still limits sensitivity.

      4. Often used in patients with nondiagnostic Holter monitoring, particularly when symptoms are infrequent. Sensitivity is 14%, compared with long-term ILR.

   5. ILRs have been used successfully in some patients with recurrent unexplained syncope. The yield in such patients has been reported at 90%. This may be particularly useful at detecting bradycardias missed by EP studies.

   6. EP studies require a right heart catheterization. During EP studies, stimuli are delivered in order to elicit tachyarrhythmias and detect accessory pathways. Bradyarrhythmias may be implied when patients have prolonged conduction times or when the sinus node responses to rapid pacing are abnormal.

      1. Sensitivity is 90% for VT.

      2. Sensitivity for bradyarrhythmias is low (33%).

      3. Overall diagnostic yield of EP studies

         • (1) 36–70% in patients with heart disease

         • (2) 22% in patients with abnormal ECGs

         • (3) 14% in select patients with normal ECGs without heart disease

      4. Indications for EP studies in patients with unexplained syncope include

         • (1) Prior MI

         • (2) Structural heart disease

         • (3) Impaired LV function

         • (4) Bifascicular block

         • (5) Monitoring suggests sinus node dysfunction or AV block

      5. Risk of EP studies include cardiac perforation, MI, AV fistulae (< 3%), deep venous thrombosis, and PE.

5. Figure 31-5 summarizes the clinical clues and diagnostic considerations in patients with possible cardiac syncope.

Reviewing Figure 31-5 for clues to potential cardiac syncope, Mr. C. dose not have any associated symptoms of palpitations, chest pain, or dyspnea with this acute event. His past medical history of CAD clearly raises the possibility of an acute coronary syndrome, which is an unusual cause of syncope. His echocardiogram confirms HF, markedly increasing his risk of VT. His ECG is consistent with his prior CAD and there are no additional ECG findings to suggest bradycardia (ie, heart block, BBB, sinus bradycardia). The leading hypothesis is revised to VT, but you wonder if this might be the presentation of an acute coronary syndrome.

Revised Leading Hypothesis: VT

Textbook Presentation

Patients with VT may be asymptomatic or have symptoms that range from palpitations to lightheadedness, near syncope, syncope, or sudden cardiac death.

VT occurs most commonly in patients with CAD and HF and should be seriously considered when patients with preexisting CAD, HF, or other heart disease present with syncope.

Disease Highlights

1. Etiology and associations

   1. Ischemic heart disease

      1. Associated with CAD in 80% of cases

      2. May be secondary to acute ischemia/MI or prior scar

   2. HF

   3. Other heart disease: HCM, valvular heart disease, infiltrative disorders

   4. Miscellaneous causes

      1. Electrolyte disorders (hypokalemia and hypomagnesemia)

      2. Hypoxia

      3. Drugs, particularly those that prolong the QT interval (eg, antiarrhythmics, antipsychotics, tricyclic antidepressants, macrolides, and some fluoroquinolones)

   5. Congenital disorders

      1. Congenital heart disease

         • (1) Long QT syndrome

           • (a) The ECG of affected families demonstrates long refractory periods (long QT intervals defined as a QTc of > 450 ms in males and 460 ms in females)

           • (b) Affected patients are at risk for sudden cardiac death from a form of VT called torsades de pointes.

           • (c) Arrhythmias may be precipitated by emotional stress, exercise, loud abrupt noises, or during sleep.

           • (d) Several symptoms typically associated with vasovagal syncope are also common in the long QT syndrome: triggered by emotional stress, pain, or noise (70%); sweating (67%); nausea (29%); situational (associated with micturition, defecation or coughing) (17%); abdominal discomfort (16%)

             Long QT syndrome may mimic vasovagal syncope. Even patients with symptoms typical of vasovagal syncope should have an ECG performed and QTc measured.

           • (e) A FH of sudden cardiac death is more common in the long QT syndrome than vasovagal syncope (66% vs. 17%)

           • (f) Associated with congenital neural deafness

         • (2) Brugada syndrome

           • (a) Unusual disorder secondary to mutation in the sodium channel gene, which predisposes patients to polymorphic VT and sudden death.

           • (b) Suggestive baseline ECG abnormalities include a right BBB pattern with ST elevation in the right precordial leads.

2. Prognosis

   1. VT is a potentially life-threatening arrhythmia.

   2. Predictors of mortality in patients with VT include prior cardiac arrest, LV dysfunction, post MI, or inducible VT on EP studies.

Evidence-Based Diagnosis

1. ECG criteria for VT

   1. ≥ 3 consecutive wide complex (QRS ≥ .12 seconds) beats (Figure 31-6) > 100 bpm constitutes a wide complex tachycardia

      1. 80–90% of wide complex tachycardias are due to VT

      2. However, supraventricular tachycardias can also occasionally manifest wide QRS complexes (> 0.12 s) due to conduction associated with a BBB or an accessory pathway, hyperkalemia or drug induced QRS changes (tricyclic antidepressants overdose and class 1a antiarrhythmics)

      3. ECG criteria that increase the likelihood that the wide complex tachycardia is due to VT include:

         • (1) Fusion beats

         • (2) Capture beats

         • (3) AV dissociation

         • (4) Concordance of the precordial leads (all chest leads pointing either up or all pointing down.)

         • (5) The absence of these findings does not establish supraventricular tachycardia.

      4. A history of CAD or HF increases the likelihood that the wide complex tachycardia is VT.

      5. Hemodynamic stability does not rule out VT.

      6. Review of prior ECGs can be helpful.

         • (1) A preexistent BBB on a prior ECG (during sinus rhythm) with the same QRS morphology as that during the arrhythmia favors supraventricular tachycardia with aberrancy.

         • (2) Evidence of WPW suggests supraventricular tachycardia with antidromic conduction down the accessory tract.

           All wide complex tachycardias should be assumed to be VT unless there is conclusive evidence of a supraventricular tachycardia (see above).

   2. Sustained VT is defined as VT lasting longer than 30 seconds.

2. In patients with risk factors for VT (eg, ischemic heart disease, HF, HCM), (but without documented VT) EP studies can provoke sustained monomorphic VT and be diagnostic. This is particularly useful in patients in whom VT is suspected and who do not already have an indication for an ICD.

Treatment

1. Patients with ongoing VT

   1. Unstable patients (with hypotension, angina, HF, or altered mental status) should receive immediate cardioversion. The management of acute VT evolves rapidly and is beyond the scope of this text. Please see appropriate ACLS guidelines.

   2. Evaluation in stable patients with ongoing VT

      1. Obtain baseline ECG and troponin to look for evidence of ischemia, long QT syndrome.

      2. Check electrolytes (especially potassium, magnesium) and SaO₂.

      3. Review of medications to search for drugs associated with QT prolongation

      4. Consultation is advised regarding antiarrhythmic therapy.

2. Follow-up evaluation is directed at evaluating the etiologies of VT and risk for sudden death.

   1. Stress testing (and coronary angiography in selected patients) can help uncover underlying ischemia precipitating VT and is recommended for patients with exercise-induced syncope or chest pain or an intermediate or greater probability of CAD.

   2. An echocardiogram should be obtained to evaluate LV function and rule out valvular heart disease and HF.

   3. EP testing is recommended for selected patients (see above).

3. Prevention of recurrent VT and sudden cardiac death

   1. Treat underlying conditions

      1. Treat ischemic heart disease (including revascularization if necessary)

      2. Treat HF (angiotensin-converting enzyme [ACE] inhibitors, beta-blockade, and spironolactone have all been shown to decrease mortality).

      3. Optimize electrolytes, including magnesium.

   2. Specific therapy for the treatment and prevention of VT includes antiarrhythmic drugs (especially beta-blockers and possibly amiodarone), catheter ablation, ICDs, and combinations of the above.

      1. ICDs are implanted devices that monitor the cardiac rhythm and automatically detect and cardiovert patients in VT.

      2. ICDs are used in selected patients at high risk for sudden death, including selected HF patients, survivors of sudden death, and patients in whom syncope was believed to have been caused by VT.

      3. Precise indications for ICD therapy are complex and influenced by the cause of heart disease (ischemic or nonischemic), the ejection fraction, the type of arrhythmia (monomorphic VT, polymorphic VT or ventricular fibrillation), and in ischemic heart disease, plans for revascularization as well as the timing of the arrhythmia relative to the most recent MI. Appropriate use criteria have been published by the ACCF/AHA.

      4. Consultation is advised.

Alternative Diagnosis: Acute Coronary Syndrome & Syncope

Acute coronary syndrome is an unusual cause of syncope and is covered extensively in Chapter 9, Chest Pain. This discussion will focus on patients who experience syncope due to an acute coronary syndrome. Briefly, acute coronary syndromes account for approximately 3% of patients presenting to emergency departments with syncope. The mechanism of syncope varies and includes reflex syncope (particularly in inferior MIs), advanced AV block (particularly in anterior MIs) and VT. Symptoms are often atypical in syncopal patients with acute MI; chest pain is present in only 17%, dyspnea in 30%, and a history of CAD in 54%. Lab abnormalities include troponin elevation on presentation (50%) and ST segment elevation (9%). Nonetheless, a normal ECG (defined as normal sinus rhythm without new or indeterminate changes) makes the diagnosis of acute MI unlikely, negative predictive value 99% (sensitivity 80%, specificity 64%, LR+ 2.2, LR– 0.31).

You still wonder if a significant bradyarrhythmia or a PE might be responsible for Mr. C’s syncope.

Alternative Diagnosis: Bradycardia from SSS

Textbook Presentation

The presentation of SSS depends on the duration and severity of the bradyarrhythmia. When the bradyarrhythmia is severe and prolonged, patients may experience sudden syncope. With less severe bradycardia, patients may experience weakness, dyspnea on exertion, angina, transient ischemic attacks, or near syncope. Since the bradyarrhythmia may be short lived, patients may recover without intervention.

Disease Highlights

1. Episodic or persistent failure of sinus node

2. Most common indication for pacemaker placement

3. Often seen in the elderly (mean age 68) due to fibrosis and degeneration of sinus node

4. Underlying CAD is common and contributes to the pathogenesis of SSS in some patients.

5. A variety of medications can depress sinus node function and aggravate SSS, including beta-blockers, verapamil, diltiazem, digoxin, cimetidine, clonidine, lithium, methyldopa, and other antiarrhythmics.

6. Less common causes include hypothyroidism, infiltrative myocardial diseases, pericarditis, Lyme disease, and rheumatic fever.

7. Electrical manifestations may include

   1. Sinus bradycardia < 40 bpm

   2. Sinus pauses > 2 seconds

   3. Sinus arrest (with an escape junctional rhythm)

   4. Sinoatrial exit block (inability of the sinus impulse to exit the sinus node)

8. Concomitant AV conduction disturbances are present in over 50% of patients with SSS.

9. Associated with supraventricular tachyarrhythmias, in 40–60% of patients, particularly atrial fibrillation (tachy-brady syndrome). Such patients may complain of palpitations. The bradycardia often follows termination of the tachycardia. Tachy-brady syndrome markedly increases the risk of death or nonfatal stroke (2- to 3-fold) compared with SSS alone.

Evidence-Based Diagnosis

1. Simultaneous symptoms and ECG findings (sinus bradycardia, significant pauses or sinus exit block) establishes the diagnosis.

2. Holter monitoring may be used but is often nondiagnostic due to the intermittent nature of the arrhythmia.

3. External cardiac continuous loop event monitors allow for a longer period of monitoring and correlation with symptoms.

4. Carotid sinus massage may cause prolonged pauses in patients with SSS (> 3 seconds).

5. ILRs have also been used.

6. Pharmacologic studies

   1. Adenosine slows sinus node activity.

   2. Small studies suggest patients with SSS have delayed sinus node recovery following adenosine administration.

   3. The diagnostic accuracy is similar to EP studies.

7. EP studies: Useful in patients with severe symptoms when monitoring has failed to capture patients during symptoms (which could confirm or exclude SSS). However, sensitivity is imperfect and normal results to not rule out SSS.

Treatment

1. Discontinue any medications that may adversely affect sinus function (see above). (If beta-blockers or other drugs cannot be discontinued, patients may require pacemaker.)

2. Indications for pacemaker placement

   1. Documented symptomatic sinus node dysfunction

   2. Chronotropic incompetence: In this condition, the sinus rate does not increase appropriately with physical activity, leading to a relative bradycardia and symptoms.

   3. Pacemakers are used in certain situations when SSS is suspected but cannot be confirmed.

      1. Patients with HR < 40 bpm and prior symptoms

      2. EP study shows long sinus node recovery time following rapid atrial pacing in patients with prior unexplained syncope.

      3. Patients with a history of syncope and asymptomatic pauses ≥ 3 s (except when asleep or young trained persons)

3. Anticoagulation is indicated for patients with SSS and concurrent atrial fibrillation (persistent or intermittent).

Alternative Diagnosis: Bradycardia due to AV Heart Block

Textbook Presentation

Depending on the duration and severity of the heart block, patients with AV block may be asymptomatic or complain of syncope, near syncope, palpitations, angina or transient ischemic attacks.

Disease Highlights

1. Secondary to conduction abnormalities in the AV node, bundle of His, or bundle branches.

2. Classification (Table 31-5)

   1. In first-degree AV block all of the sinus impulses (P waves) are conducted (but the PR interval is prolonged)

   2. In second-degree block, some of the impulses are conducted.

   3. In third-degree AV block, none of the P waves are conducted (Figure 31-7).

   4. In second- or third-degree AV block, the ventricular rate slows and may depend on lower intrinsic pacemakers residing within the ventricle. The bradycardia can result in dyspnea, angina, hypotension, syncope, or death.

3. AV nodal disease should also be suspected in patients with atrial fibrillation who have a slow ventricular response and are not taking medications that slow AV conduction (eg, digoxin, beta-blockers, verapamil, or diltiazem).

4. Etiology

   1. Fibrosis of the conduction system

   2. Ischemic heart disease

   3. Medications (eg, beta-blockers, verapamil, diltiazem, digoxin, amiodarone)

      The combination of verapamil and beta-blockers should always be avoided. There is a high incidence of subsequent AV block and HF.

   4. Hyperkalemia

   5. Valvular heart disease (due to extension of calcification into the conduction system)

   6. Increased vagal tone

   7. Miscellaneous other causes (Lyme disease, sarcoidosis, etc)

Treatment

1. Discontinue medications that impair AV conduction.

2. Treat ischemia.

3. Correct electrolyte abnormalities.

4. Atropine can be useful in emergent situations.

5. Pacemakers

   1. Precise indications are complex. The ACC/AHA published guidelines in 2008.

   2. Pacing is recommended for patients with third-degree AV block and symptomatic second-degree AV block.

   3. Pacing is usually recommended for patients with Mobitz II second-degree AV block.

   4. Pacing is also recommended for advanced second-degree AV block (defined as 2 consecutively blocked P waves) associated with any of the following: symptoms, pauses while awake ≥ 3 sec, HR < 40 bpm while awake, escape rhythms below the AV node or atrial fibrillation with ventricular pauses of ≥ 5 sec.

   5. Pacing is not usually indicated in Mobitz I second-degree AV block.

   6. Pacing is not indicated in asymptomatic first-degree AV block.

Alternative Diagnosis: PE

Textbook Presentation

PE is an unusual cause of syncope (about 1%) and is covered extensively in Chapter 15, Dyspnea. This discussion will focus on patients who experience syncope due to PE. Between 9% and 24% of patients with PE experience syncope (39% in patients with massive PE). Syncope in PE is usually secondary to massive embolization involving more than 50% of the pulmonary vascular bed, critically limiting blood return to the LV and cardiac output. This massive embolization increases the likelihood of findings consistent with more extensive PE including hypotension (ranging from 14% to 76% in various studies), cardiac arrest (24%), and ECG evidence of cor pulmonale (S1Q3T3 or new right BBB in 60%). Patients with PE who experience syncope are twice as likely to have right ventricular dysfunction as patients who do not experience syncope (17.4% vs 8.5%).

Despite this, the subset of patients with PE and syncope who survive to arrive at the hospital have often stabilized due to clot fragmentation and may be hemodynamically stable and relatively asymptomatic. Dyspnea has been reported in 50–90% of patients, hypoxia (PaO₂ < 60 mm Hg) in 91%.

PE should be considered in the differential diagnosis of patients with syncope who have symptoms of dyspnea, chest pain, or risk factors for PE; physical exam findings of unexplained hypotension, tachycardia, JVD, a loud S₂, or a right-sided S₃ gallop; hypoxia; ECG findings of a S1Q3T3 pattern, right axis deviation, or right BBB; radiographic findings of an unexplained pleural effusion or infiltrate (that may suggest a pulmonary infarction); or echocardiographic findings of right atrial or right ventricular enlargement.

The sensitivity of telemetry is inadequate to exclude life-threatening arrhythmias such as VT. Furthermore, none of the alternative diagnoses are suggested by the history, physical exams, or laboratory test results (such as orthostatic hypotension, PE, SSS, or AV heart block). After careful discussion with Mr. C, you order an EP study.

The remarkable feature of Mrs. S’s history is the prolonged period of lethargy and confusion that persisted until she reached the emergency department. As discussed at the beginning of the chapter, and illustrated in Figure 31-1, patients with syncope suffer from transient global cerebral hypoperfusion and rapid restoration of normal consciousness. Mr. S’s prolonged confusion is a pivotal clue that suggests a non-syncopal etiology for her loss of consciousness. Diagnostic considerations include seizure, hypoglycemia, or another neurologic event (eg, an ischemic event involving the posterior circulation or trauma). The patient’s bruised tongue is a diagnostic fingerprint that markedly increases the likelihood of a seizure. Hypoglycemia-induced syncope is usually preceded by either confusion or sympathetic stimulation producing tremulousness, nervousness, or diaphoresis and occurs almost exclusively in diabetic patients taking insulin, sulfonylureas, or thiazolidinediones. Table 31-6 lists the differential diagnosis.

Patients with syncope should be asked, “What was the next thing you remember?” Patients who do not remember the ambulance ride or suffer a period of amnesia following the event (> 5 minutes) should be evaluated for seizures.

Leading Hypothesis: Seizures

Textbook Presentation

Generalized seizures classically present with tonic-clonic activity, loss of postural tone, incontinence, and a prolonged postictal period of lethargy. The purpose of this review is to focus on features that help distinguish seizures from syncope.

Disease Highlights

1. 3% of US population suffers a seizure in their lifetime

2. Seizures are the cause of syncope in 1–7% of patients.

3. Etiology of seizure and prevalence in patients over age 60

   1. Idiopathic, 35%

   2. Ischemic, 49%

   3. CNS tumor, 11%

      1. Primary, 35%

      2. Metastatic, 59%

   4. CNS trauma, 3%

   5. CNS infection, 2%

   6. Metabolic disturbances

      1. Hypoglycemia and hyperglycemia (marked)

      2. Hypoxia

      3. Hyponatremia

      4. Hypocalcemia

      5. Uremia

   7. Medications (Numerous medications have been implicated. Some commonly used medications that cause seizures (albeit rarely) include cyclosporine, fentanyl, meperidine, lidocaine, phenothiazines, quinolones, theophylline, tricyclic antidepressants, and bupropion.)

   8. Illicit drugs (ie, methylenedioxymethamphetamine [MDMA; Ecstasy], cocaine)

   9. Withdrawal states (ie, alcohol, baclofen, benzodiazepines, and opioids)

Evidence-Based Diagnosis

1. Postictal confusion is the most sensitive clinical feature (Table 31-7). The absence of a postictal period makes seizures an unlikely cause of syncope (sensitivity 94%, LR− 0.09).

2. Tongue laceration, head turning, and unusual posturing are the most specific clinical features and substantially increase the likelihood of seizure (specificity 97%, LR+ 12–15).

3. Certain symptoms are unusual in patients with seizures and reduce the likelihood of seizure.

   1. Diaphoresis preceding spell, LR 0.17

   2. Chest pain preceding spell, LR 0.15

   3. Palpitations, LR 0.12

   4. Dyspnea prior to spell, LR 0.08

   5. CAD, LR 0.08

   6. Syncope with prolonged standing, LR 0.05

4. Convulsive syncope

   1. Limb jerking is not entirely specific for seizures.

   2. 15–90% of patients with syncope not related to seizures experience limb jerking, a phenomenon referred to as convulsive syncope. Limb jerking due to syncope is associated with myoclonic jerks, which should be distinguished from tonic-clonic activity.

      1. Myoclonic jerks tend to be arrhythmic and asymmetric, whereas the opposite is true of tonic-clonic activity.

      2. Myoclonic jerks tend to be briefer (average of 6.6 seconds) than tonic-clonic activity seen in seizures (≈ 1 minute)

      3. Myoclonic jerks never precede collapse, whereas tonic-clonic activity may precede collapse.

   3. Finally, unlike generalized seizures, which are usually associated with a significant postictal period, convulsive syncope is not associated with a significant postictal period (< 1 minute).

   4. Convulsive syncope has been reported in most diseases that cause syncope (cardiac arrhythmias (VT, WPW, heart block, long QT syndrome), aortic stenosis, carotid hypersensitivity, vasovagal syncope, and orthostatic hypotension.

   5. Patients who appear to have refractory “seizure disorders” and nonspecific abnormalities on electroencephalogram (EEG) should undergo a cardiac evaluation to rule out convulsive syncope with myoclonic jerks.

5. A point score to distinguish seizures from syncope has been developed (Table 31-8). Point scores of ≥ 1 suggest seizures (sensitivity, 94%; specificity, 94%; LR+, 16; LR−, 0.06).

6. Evaluation

   1. EEG

      1. Indicated in the evaluation of patients with possible seizures

      2. Sensitivity (between episodes) of the spike and wave pattern is 35–50% (increased with sleep deprivation)

      3. Specificity 98%

   2. Neuroimaging

      1. 37% of adults with new-onset seizures have structural lesions (eg, tumors, strokes)

      2. 15% of adults with new-onset seizures and nonfocal neurologic exams have structural lesions on neuroimaging.

      3. Indicated in all adults with new-onset seizures.

      4. In acute cases, a noncontrast CT is often performed to rule out an intracranial bleed. Follow-up MRI is recommended due to its increased sensitivity for both tumor and stroke.

   3. Sodium, calcium, glucose, BUN, creatinine, and oxygen saturation should be measured.

   4. Lumbar puncture

      1. A lumbar puncture should be considered if CNS infection is suspected (ie, patient is immunocompromised or has fever, meningismus, headache, or persistent confusion).

      2. Elevated intracranial pressure should be excluded prior to a lumbar puncture (usually with neuroimaging) in order to prevent lumbar puncture–induced herniation.

      3. Platelet count, prothrombin time, and partial thromboplastin time should be checked prior to lumbar puncture. (Thrombocytopenia and coagulopathies increase the risk of bleeding at the lumbar puncture site and subsequent spinal cord compression secondary to hemorrhage.)

   5. Toxicology screen should be ordered if illicit drug use is suspected.

   6. Elevated levels of serum neuron specific enolase can suggest generalized seizures versus other causes of syncope. Levels > 11.5 ng/mL had a sensitivity of 58%, specificity of 91%, an LR+ of 6.4, and LR– of 0.46.

   7. Prolactin measurement: American Academy of Neurology concluded that serum prolactin levels cannot be used to distinguish seizures from syncope.

Treatment

Anticonvulsant therapy is complex and evolves rapidly (see neurology texts).

The patient’s bruised tongue and postictal period strongly suggest seizures despite the lack of a previously known seizure disorder or witnesses to the event. You also wonder if an acute stroke is likely and if additional imaging of the extracranial or intracranial vessel is warranted.

Alternative Diagnosis: Cerebrovascular Disease & Syncope

Although physicians commonly consider carotid artery obstruction in the differential diagnosis of patients with syncope, unilateral obstruction of the carotid will not result in syncope. Therefore, evaluation of the anterior circulation is not indicated in the patient with syncope. On the other hand, obstruction of the posterior circulation may cause transient loss of consciousness by causing ischemia in the reticular activating system. This may occur in the subclavian steal syndrome, vertebrobasilar insufficiency, and basilar artery occlusion. These disorders are almost invariably associated with neurologic signs or symptoms and should be considered whenever patients have syncope and other symptoms referable to the brainstem (ie, diplopia, vertigo, ataxia, and weakness) (see Chapter 14, Dizziness). Finally, patients in whom subarachnoid hemorrhage develops can present with syncope. Such patients inevitably also complain of severe headache or confusion. Evaluation includes emergent noncontrast head CT scan.

The EEG confirms new-onset seizures. Since structural lesions are common in adults with new-onset seizures, neuroimaging is required.

As noted in Figure 31-1 the first step ascertains whether Mrs. P suffered from syncope or some other transient loss of consciousness. The history of rapid recovery without intervention, or history of trauma or intoxication, strongly suggests syncope. The next step considers whether this is likely due to reflex syncope, orthostatic syncope, or cardiac syncope. Several features of Mrs. P’s syncope are noteworthy. First, her syncope occurred in association with abdominal pain raising the possibility of vasovagal syncope. Second, she had 2 episodes of syncope upon standing. This pivotal clue raises the possibility of orthostatic syncope from either dehydration, hemorrhage, medications, or autonomic dysfunction. Finally, cardiac syncope should be considered in all patients with syncope. Fortunately, Mrs. P has no prior history of heart disease that would increase the likelihood of cardiac syncope. Additionally, she has no suggestive symptoms (syncope with chest pain, syncope with exertion, syncope while supine, palpitations, or dyspnea), or risk factors (prior history of heart disease) or signs (significant murmur, gallop or JVD) to suggest cardiac syncope. Her ECG is also normal. The combination of the lack of underlying heart disease or suggestive symptoms of cardiac syncope, coupled with recurrent syncope immediately after standing makes orthostatic syncope likely and cardiac syncope unlikely. Table 31-9 lists the differential diagnosis.

As discussed in the first case presentation, vasovagal syncope is often precipitated by pain, is brief, and is followed by a rapid restoration of consciousness. Many of Mrs. P’s features are consistent with this diagnosis. However, both episodes of syncope occurred immediately after standing providing a clue that her syncope was in fact orthostatic. In addition, although her abdominal pain is improved, it is still unexplained. You elect to check her BP and pulse for orthostatic change.

The patient’s volume status is always assessed utilizing clinical, not just laboratory findings. Orthostatic measurement of BP and pulse are critical. Life-threatening hypovolemia may be overlooked if the BP and pulse are not measured while the patient is standing.

Mrs. P’s profound drop in BP upon standing and recurrent syncope is a key pivotal clue and clearly indicate that she is syncopal due to orthostatic hypotension. This is not consistent with reflex syncope. You revise the leading hypothesis to syncope due to orthostatic hypotension.

Leading Hypothesis: Orthostatic Hypotension

Textbook Presentation

Orthostatic hypotension commonly presents with syncope or other symptoms (near syncope, visual blurring, weakness, leg buckling) when arising. Orthostatic hypotension should be distinguished from orthostatic dizziness, which describes symptoms on standing which may or may not be secondary to orthostatic hypotension. (Orthostatic dizziness may also be secondary to visual disturbances.) Patients with orthostatic hypotension often have obvious sources of fluid or blood loss. Common causes include vomiting, diarrhea, inadequate fluid intake, or GI bleeding (presenting as hematemesis, melena, or bright red blood per rectum). Importantly, orthostatic hypotension may develop secondary to massive but occult internal bleeding (rupture of abdominal aortic aneurysm, splenic rupture, retroperitoneal hemorrhage, or ruptured ectopic pregnancy). Finally, orthostatic hypotension may occur without volume loss, particularly in the elderly. Common causes include drugs and neurologic disorders.

Disease Highlights

1. Orthostatic hypotension occurs in 20% of patients over 75 and accounts for 12–30% of patients with syncope.

2. Etiology

   1. Hypovolemia

      1. Dehydration

         • (1) Decreased oral intake

         • (2) GI losses (vomiting, diarrhea)

         • (3) Urinary losses

           • (a) Uncontrolled diabetes mellitus

           • (b) Salt losing nephropathy

           • (c) Adrenal insufficiency

         • Hemorrhage

           • (1) GI

           • (2) Ruptured abdominal aortic aneurysm

           • (3) Ruptured spleen

           • (4) Ruptured ectopic pregnancy

   2. Over-dialysis

   3. Postprandial hypotension, particularly common in the elderly and worse with large carbohydrate meals or alcohol ingestion. Splanchnic pooling decreases venous return.

   4. Hot environments (hot tubs, baths, saunas)

3. Medications

   1. Alpha-blockers

   2. Diuretics

   3. Vasodilators (ie, nitrates, calcium channel blockers, hydralazine)

   4. ACE inhibitors and angiotensin receptor blockers (ARBs)

   5. Tricyclic antidepressants

   6. Phenothiazines and selective serotonin reuptake inhibitors

   7. Sildenafil and other phosphodiesterase inhibitors particularly when combined with nitrates

   8. Alcohol and opioids

4. Autonomic insufficiency (characterized by a fall in BP upon standing without a concomitant increase in pulse)

   1. Central neurologic disorders (ie, Parkinson disease, multisystem atrophy, pure autonomic failure, multiple sclerosis, and numerous others)

   2. Peripheral neurologic disorders: Diabetes mellitus, vitamin B₁₂ deficiency, uremia, and other causes of autonomic neuropathies

   3. Prolonged bed rest

Evidence-Based Diagnosis

1. Definition of orthostatic hypotension

   1. ≥ 20 mm Hg decrease in systolic BP within 3 minutes of standing; a decrease in systolic BP of ≥ 30 mm Hg may be a more appropriate criterion in patients with hypertension

   2. > 10 mm Hg decrease in diastolic BP within 3 minutes of standing

   3. Or > 30 bpm increase in pulse within 3 minutes of standing

2. The presence of orthostatic hypotension does not confirm that syncope was secondary to orthostatic hypotension. Syncope from orthostatic hypotension should be diagnosed in patients with orthostatic hypotension and syncope or presyncope on standing.

3. Orthostatic hypotension associated with volume loss (dehydration or hemorrhage)

   1. Several studies assessed the impact of phlebotomy on volunteers. Phlebotomy removed a moderate (450–630 mL) to large (630–1150 mL) volume of blood.

      1. An increase in pulse of > 30 bpm with standing is both highly sensitive for large volume blood loss (97%) and highly specific (98%, LR+ 48) (Table 31-10). The sensitivity falls dramatically if the patient sits instead of stands (39–78%).

      2. Simple supine measurements of BP and pulse were not sensitive for even large blood loss (sensitivity 12–33%).

      3. Any abnormal finding on orthostatic maneuvers strongly suggested volume loss (specificity 94–98%; LR+, 3.0–48).

      4. The sensitivity of orthostatic measurements is greatest if the supine and standing BPs are compared. If the supine BP is not measured, 67% of orthostatic patients may not be identified.

      5. Patients should stand for 1 minute before the measurement of the upright BP.

      6. No measure was very sensitive for moderate blood loss (0–27%).

   2. Profound blood loss may occasionally paradoxically produce bradycardia. (The reduction in end-systolic volume may trigger the neurally mediated reflex.)

   3. The admission HCT does not accurately reflect the severity of acute hemorrhage. A fall in HCT may take 24–72 hours.

   4. A history of nausea, vomiting, diarrhea, or inadequate intake can suggest volume depletion that is supported by elevations in BUN, creatinine and/or low urinary Na+, FE_Na+ or FE_urea.

Treatment

1. Acute blood loss: Blood transfusion is appropriate in the orthostatic patient with acute blood loss.

2. Dehydration (diarrhea, vomiting, or decreased oral intake)

   1. Patients able to tolerate oral intake: oral rehydration

   2. Patients unable to tolerate oral intake: IV hydration

      1. Normal saline is preferred.

      2. Usually 500 mL to 1 L boluses are given over 1 hour.

      3. Smaller boluses may be given to fragile patients (ie, small elderly women or those with a history of kidney disease or HF).

      4. Repeat orthostatic BP measurements are made following each bolus as well as a lung and cardiac exam to ensure the patient has not received excessive fluid.

      5. Bolus therapy should be continued until orthostatic hypotension resolves.

3. Chronic orthostatic hypotension

   1. Hydration (water, soup, or sports drinks)

   2. Discontinue offending medications (diuretics, alpha-blockers, nitrates, tricyclic antidepressants, phenothiazines).

   3. Patients are advised to arise slowly (sitting on the side of the bed, prior to standing), avoid large meals and excessive heat, and use waist high support hose.

   4. Support stockings to the waist and exercise programs can be helpful.

   5. Alpha-agonists (ie, midodrine) have also been used successfully. Side effects include urinary retention, hypertension, and worsening HF.

   6. Other drugs that have been used with less conclusive evidence include fludrocortisone, nonsteroidal antiinflammatory drugs, caffeine, and erythropoietin in anemic patients.

It is important to remember that Mrs. P presented with syncope and abdominal pain. Although the pain has improved, it has not resolved; it may provide an important clue to the underlying etiology. Given the profound orthostatic hypotension and the lack of external blood or volume loss, or incriminating medication, internal bleeding must be considered as a source of her abdominal pain and syncope. In the differential diagnosis you consider splenic rupture, ruptured abdominal aortic aneurysm, and ruptured ectopic pregnancy. The lack of trauma argues against splenic rupture and the patient’s age and gender are atypical for abdominal aortic aneurysm. You wonder if in fact she has suffered from a ruptured ectopic pregnancy.

It is important to remember the patient’s chief complaint because it usually holds the most important clue to the diagnosis.

Although the final diagnosis of ectopic pregnancy was not considered initially, a careful clinical exam confirmed orthostatic syncope. Once that pivotal clue was discovered, the differential diagnosis could be narrowed and the underlying cause determined. It is instructive to note that her initial HCT was normal because the remaining intravascular blood had not yet been diluted by any oral or IV fluids.

Initial HCT measurements will not accurately reflect the magnitude of blood loss in a patient with recent hemorrhage.

Aortic Stenosis

Textbook Presentation

Aortic stenosis is usually diagnosed incidentally during routine exam rather than due to symptoms. Typically, aortic stenosis produces a loud crescendo-decrescendo systolic murmur at the right second intercostal space, which may radiate to the neck. When aortic stenosis becomes severe, patients may have any of the 3 cardinal symptoms: HF (dyspnea, typically with exertion), syncope, or angina.

Disease Highlights

1. Thickening and calcification of valve leaflets results in progressive obstruction to blood flow.

2. LVH develops to compensate for the obstruction.

3. Pathophysiology of symptoms is shown in Figure 31-8.

4. Prevalence is 3% in patients ≥ 75 years old.

5. Etiology

   1. Degeneration of a previously normal valve

   2. Congenital bicuspid valve

      1. 1–2% of population is born with congenital bicuspid valve.

      2. Severe aortic stenosis develops in 66% of patients and at an earlier age than in patients with tricuspid valves.

      3. Aortic root structure is usually abnormal and often associated with progressive dilation of the aortic root that may require repair to prevent rupture or dissection.

   3. Rheumatic heart disease

6. Severe aortic stenosis is characterized by valve area < 1 cm or mean aortic valve gradient > 40 mm Hg. Gradients may be lower in patients with a low cardiac output.

7. Prognosis: Mortality increases markedly when symptoms develop (HF, angina, or syncope). The most common symptoms are decreased exercise tolerance and dyspnea on exertion. Mortality for symptomatic patients not undergoing valve replacement:

   1. Aortic stenosis and angina: 50% 5-year mortality

   2. Aortic stenosis and syncope: 50% 3-year mortality

   3. Aortic stenosis and dyspnea: 50% 2-year mortality

8. Other late manifestations:

   1. Atrial fibrillation may develop. This is often poorly tolerated because the LV is noncompliant and dependent on atrial contraction for filling.

   2. An increased bleeding tendency secondary to disruption of large von Willebrand multimers by the abnormal aortic valve.

Evidence-Based Diagnosis

1. History and physical exam: Most studies demonstrate only a fair reproducibility between examiners.

   1. Findings that help rule in aortic stenosis

      1. Effort syncope in patients with a systolic murmur (LR+ 1.3–∞, LR− 0.76)

      2. Slow carotid upstroke (sensitivity, 15–42%; specificity, 95–100%; LR+ 9.2–∞)

      3. Murmur radiating to right carotid (sensitivity, 71–73%; specificity, 90%; LR+ 7.5)

   2. Findings that help rule out aortic stenosis

      1. Absence of any murmur (LR− 0.0)

      2. Absence of murmur below right clavicular head (LR− 0.1)

   3. Murmurs may be less intense in patients with superimposed HF.

2. Doppler echocardiogram

   1. The initial test of choice to assess for aortic stenosis

   2. Recommended for patients with a systolic murmur ≥ grade III/VI

   3. Aortic stenosis is graded as mild if the valve area is > 1.5 cm², moderate if the valve area is 1–1.5 cm², severe if the valve area < 1.0 cm² and critical if the valve area is < 0.8 cm².

   4. Surveillance echocardiography is recommended to monitor progression (every 6 months for severe aortic stenosis, and every year for mild to moderate aortic stenosis associated with significant calcification). Echocardiography is also recommended for any change in symptoms or signs and during pregnancy.

   5. Patients with bicuspid aortic valves and aortic stenosis or dilation of the aortic root (> 40 mm) should have annual echocardiography. In patients without stenosis or dilatation, echocardiography is recommended every 2 years.

Treatment

1. Since the prognosis changes markedly in symptomatic patients, patients with severe asymptomatic aortic stenosis should be reevaluated every 6 months and queried about HF symptoms, angina, or syncope. Patients should also be instructed to report new symptoms.

2. Symptomatic patients should undergo mechanical correction, not medical therapy.

3. While awaiting surgery, patients with HF symptoms may be treated cautiously with diuretics, ACE inhibitors, and digoxin (if there is systolic dysfunction).

4. Mechanical correction:

   1. Valve replacement is guided almost exclusively by symptoms.

   2. Definite indications for valve replacement

      1. Severe aortic stenosis in symptomatic patients

      2. Severe aortic stenosis in asymptomatic patients undergoing coronary artery bypass surgery, other valve surgery, or surgery on the ascending aorta.

      3. Severe aortic stenosis in asymptomatic patients with ejection fraction < 50%.

   3. Standard preoperative evaluation includes angiography in many patients to determine whether the patient needs concomitant coronary artery bypass surgery. This includes patients with symptoms of CAD or CAD risk factors (including men ≥ 35, postmenopausal women, or premenopausal women ≥ 35 with CAD risk factors).

   4. Mechanical and bioprosthetic valves have been used.

      1. Mechanical valves have greater durability and a significantly lower rate of failure and need for replacement. They are associated with a lower all-cause mortality than bioprosthetic valves.

      2. Mechanical valves are associated with an increased risk of thromboembolism and infection. Vitamin K antagonists (target INR 2.5) are recommended. In addition to warfarin, aspirin is recommended at 50–100 mg/day for patients at low risk for bleeding.

      3. Bioprosthetic valves

         • (1) Reserved for patients who have a contraindication to warfarin therapy or who are noncompliant.

         • (2) May be used in patients over 65 (whose life expectancy makes the need for a second replacement unlikely).

         • (3) Aspirin 50–100 mg/day recommended.

      4. Another alternative is the Ross procedure in which the pulmonary valve is removed and used as the aortic valve. The pulmonary artery is reconstructed to create the pulmonary valve. The survival of these grafts is good and patients do not require anticoagulation therapy. In-hospital surgical mortality may be higher with this procedure.

   5. Recent experience has increased with transcatheter aortic valve implantation (TAVI).

      1. An option for patients who are not surgical candidates (note that age alone is not a contraindication to aortic valve replacement).

      2. Superior to medical management in nonoperable patients with severe symptomatic aortic stenosis. Mortality was reduced (absolute risk reduction 20%, NNT 5) although strokes increased (absolute increased risk 5%, NNH 20)

      3. Comparable in mortality and stroke rate to aortic valve replacement in patients with a high surgical risk. TAVI is associated with higher rates of major vascular complications but lower rates of major bleeding and shorter hospital stays. Indications and patient selection are actively evolving.

   6. Balloon valvotomy is a poor option.

      1. Provides only temporary relief (6–12 months) and does not improve survival.

      2. Complications occur in > 10%.

      3. Reserved for palliation in patients with other serious (or lethal) comorbidities and as a bridge to TAVI or aortic valve replacement in patients who are hemodynamically unstable or require urgent major noncardiac surgery.

      4. An exception to this may be the young adult with noncalcific aortic stenosis in whom balloon valvotomy is a viable option.

5. Vigorous exercise should be discouraged in patients with moderate to severe aortic stenosis.

Situational Syncope

A variant of reflex syncope, situational syncope occurs during or immediately after micturition, defecation, swallowing, or coughing which increase vagal tone.

Carotid Sinus Syndrome

Textbook Presentation

Carotid sinus syndrome (CSS) is another variant of reflex syncope. Patients typically complain of syncope or falls that may be precipitated by pressure applied to the carotid (eg, head turning, buttoning collar, shaving, or cervical motion) or occur spontaneously.

Disease Highlights

1. Carotid sinus hypersensitivity (CSH) represents a syndrome of increased carotid sensitivity with resultant bradycardia, hypotension, or both.

2. Increasingly common in the elderly in whom it may account for 15% of recurrent syncopal events. Unusual in patients < 40 years old.

3. 15–56% of affected patients complain of falls but deny syncope.

   1. May be due to retrograde amnesia or alternatively hypotension that is insufficient to maintain an upright posture but sufficient to avoid frank loss of consciousness.

   2. CSS present in 19–27% of patients with unexplained falls but 0% in patients with accidental falls.

      Consider CSS in elderly patients with unexplained falls.

Evidence-Based Diagnosis

1. CSH should be distinguished from CSS.

   1. CSH refers to a significant drop in pulse (≥ 3-second pause) or systolic BP (≥ 50 mm Hg drop in BP) accompanying pressure on the carotid artery. CSS is diagnosed in patients with CSH and spontaneous syncope.

   2. CSH occurs in 35% of asymptomatic elderly patients without prior falls, dizziness, or syncope.

   3. Given the frequency of CSH in an asymptomatic population, care must be taken before ascribing the cause of syncope to CSH.

   4. CSS occurs in only 5% of elderly patients without prior falls, dizziness, or syncope, suggesting it is a more specific finding than CSH alone.

2. 47% of patients report symptoms precipitated by head movement of looking upward.

3. Carotid sinus massage is used in the diagnosis of CSS.

   1. Carotid sinus massage is applied (unilaterally) for 5–10 seconds during continuous ECG and BP monitoring. Carotid sinus massage needs to be performed on each side separated in time by ≥ 1 minute and in the supine and then upright position.

   2. The inhibitory response is unilateral in 81% of patients.

   3. 30–50% of patients have findings only when upright.

4. Carotid sinus massage is contraindicated in patients with carotid bruits, recent cerebrovascular accident or transient ischemic attack within the last 3 months, MI (within 6 months), or severe dysrhythmias.

5. Carotid sinus massage has been complicated by transient and permanent neurologic symptoms in 0.3% and 0.05% of patients, respectively.

Treatment

Pacemakers are indicated in syncopal patients with cardioinhibitory CSS with documented symptomatic asystole of ≥ 3 sec with carotid sinus massage in whom they have been demonstrated to reduce the incidence of subsequent syncope and falls.

Wolff-Parkinson-White (WPW) Syndrome

Textbook Presentation

WPW syndrome may be asymptomatic or present with palpitations, near syncope, syncope, or sudden death. In asymptomatic cases, the diagnosis may only be made after typical findings are discovered on an ECG performed for some other reason.

Disease Highlights

1. A congenital disorder in which an accessory bundle directly connects the atria and ventricular muscle bypassing the AV node.

2. A variety of life-threatening arrhythmias may develop that may cause syncope or sudden cardiac death. These include

   1. Antidromic tachycardia in which an impulse spreads down the accessory pathway and then back up the His-Purkinje system in a retrograde fashion. This reentrant loop can result in rapid tachycardias, hypotension, syncope, and sudden death.

   2. The reentrant loop may run in the opposite direction (orthodromic tachycardia, Figure 31-9).

   3. Finally, atrial fibrillation or flutter can develop. In patients with atrial fibrillation or flutter, the accessory pathway facilitates rapid conduction of the atrial tachycardia into the ventricles allowing rapid ventricular depolarization and putting patients at risk for syncope or sudden death.

3. Syncope in patients with WPW is associated with a greater frequency (25%) of rapid, life-threatening, conduction over the accessory pathway.

Evidence-Based Diagnosis

1. Baseline ECG abnormalities during normal sinus rhythm may reveal a combination of a short PR interval and a delta wave.

   1. Short PR interval

      1. In healthy persons, the normal PR interval is produced by a built-in delay at the AV node (designed to allow atrial emptying prior to ventricular systole).

      2. In WPW syndrome, the accessory pathway bypasses the AV node and initiates ventricular depolarization without such a delay; this results in a shortened PR interval in 75% of patients (Figure 31-10).

   2. Delta wave

      1. In most patients with WPW syndrome, the accessory pathway inserts directly into ventricular muscle (rather than into the specialized His-Purkinje system).

      2. Ventricular depolarization spreads slowly from cell to cell through gap junctions, rather than rapidly through the specialized His-Purkinje conduction system.

      3. This results in slow ventricular depolarization and the slow initial upstroke of the QRS complex known as the delta wave (Figure 31-10).

      4. Finally, as this ventricular depolarization progresses, the AV node is also processing the supraventricular impulse. Eventually, the impulse passes through the AV node, activates the His-Purkinje system and causes rapid depolarization. This results in a narrow terminal portion of the QRS complex.

Treatment

1. Risk stratification

   1. Stress tests can provide prognostic information

      1. In certain patients, the accessory pathways cannot conduct at rapid heart rates (due to a long refractory period) and the patients are at low risk for life-threatening arrhythmia from WPW.

      2. Stress tests can monitor for loss of conduction during rapid heart rates. Patients whose surface ECG demonstrates clear loss of conduction down the bypass tract at rapid heart rates (normalization of the PR interval and loss of the delta wave) are unlikely to suffer from rapid WPW related arrhythmias.

      3. Patients whose bypass tract continues to conduct at rapid heart rates are at greater risk for rapid life-threatening arrhythmias and are candidates for more extensive evaluation with EP studies.

   2. EP studies can be useful for diagnosis, prognosis, and therapy.

      1. EP studies can confirm the presence of a bypass tract.

      2. EP studies can measure the conduction characteristics of the bypass tract to determine if it can sustain rapid life-threatening arrhythmias.

      3. Radiofrequency ablation can obliterate the bypass tract in high-risk patients.

      4. An EP studies is typically offered to the following patients:

         • (1) Symptomatic patients (eg, history of tachycardia, syncope, or sudden death)

         • (2) Patients with structural heart disease who are at a higher risk for atrial fibrillation

         • (3) Healthy patients whose stress test does not demonstrate loss of preexcitation at rapid heart rates.

2. Treatment

   1. Immediate management: A variety of options exist for patients with acute WPW-related arrhythmias, including electrical cardioversion and pharmacotherapy. The choice of pharmacotherapy is dependent on the mechanism of the tachycardia. Consultation is recommended.

   2. Long-term management

      1. Long-term therapeutic options include pharmacologic therapy and radiofrequency catheter ablation of the bypass tract.

      2. Radiofrequency ablation can be performed if the risk of rapid tachycardias is high.

      3. Consultation is recommended.