Park's Pediatric Cardiology for Practitioners, 6th Ed.

Syncope

Prevalence

The prevalence of syncope and near syncope in children is unknown, but it is estimated that as many as 15% of children and adolescents will have a syncopal event between the ages of 8 and 18 years. The incidence may be as high as 3% of emergency department visits in some areas. Before age 6 years, syncope is unusual except in the setting of seizure disorders, breath holding, and cardiac arrhythmias.

Definition

• Syncope is a transient loss of consciousness and muscle tone that result from inadequate cerebral perfusion.

• Presyncope is the feeling that one is about to pass out but remains conscious with a transient loss of postural tone. It is usually less serious than syncope and is often a manifestation of a benign condition.

• Dizziness is the most common prodromal symptom to the above. It is a nonspecific symptom that may include vertigo and lightheadedness. The patient may say “My head is spinning” or “The room is whirling” to describe vertigo (a manifestation of vestibular disorder). Lightheadedness often accompanies hyperventilation and is frequently associated with psychological distress, including anxiety, depression, and panic attacks.

• Although most of these complaints are benign in the pediatric age group, any of these complaints could represent a serious cardiac condition that could cause sudden death.

Causes

The normal function of the brain depends on a constant supply of oxygen and glucose. Significant alterations in the supply of oxygen and glucose may result in a transient loss or near loss of consciousness with manifestations of syncope, presyncope, or dizziness. The differential diagnosis of syncope is rather broad. It may be due to noncardiac causes (usually autonomic dysfunction), cardiac conditions, neuropsychiatric conditions, and metabolic disorders. Box 31-1 lists possible causes of syncope.

In contrast to adults, in whom most cases of syncope are caused by cardiac problems, in children and adolescents, most incidents of syncope are benign, resulting from vasovagal episodes (probably the most common cause), orthostatic intolerance syndromes, dehydration (or inadequate hydration), hyperventilation, and breath holding. However, the primary purpose of the evaluation of patients with syncope is to determine whether the patient is at increased risk for death.

In this chapter, only circulatory causes of syncope are discussed in some detail. Discussion of the metabolic and neuropsychiatric causes of syncope is beyond the scope of this book.

Noncardiac Causes of Syncope

Orthostatic Intolerance

Orthostatic intolerance encompasses disorders of blood flow, heart rate, and blood pressure (BP) regulation that are most easily demonstrable during orthostatic stress yet are present in all positions. Improved understanding of changes in these parameters is the result of the recently popularized head-up tilt test. Three easily definable entities of orthostatic intolerance include vasovagal syncope, orthostatic hypotension, and postural orthostatic tachycardia syndrome (POTS).

BOX 31-1 Causes of Syncope

Autonomic (Noncardiac)

Orthostatic intolerance Group

Vasovagal syncope (also known as simple syncope, neurocardiogenic syncope, or neutrally mediated syncope)

Orthostatic (postural) hypotension (dysautonomia)

Postural orthostatic tachycardia syndrome

Exercise-related syncope

Uncited

Situational syncope

Breath holding

Cough, micturition, defecation, and so on

Carotid sinus hypersensitivity

Excess vagal tone

Uncited

Cardiac

Arrhythmia

Tachycardia: SVT, atrial flutter or fibrillation, VT (seen with long QT syndrome, arrhythmogenic RV dysplasia, Brugada syndrome)

Bradycardias: sinus bradycardia, asystole, complete heart block, pacemaker malfunction

Obstructive lesions

Outflow obstruction: AS, PS, hypertrophic cardiomyopathy, pulmonary hypertension

Inflow obstruction: MS, tamponade, constrictive pericarditis, atrial myxoma

Myocardial

Coronary artery anomalies, hypertrophic cardiomyopathy, dilated cardiomyopathy, MVP, arrhythmogenic RV dysplasia.

Neuropsychiatric

Anxiety disorders: panic disorders, agoraphobia (fear of open space or uncontrollable social situations)

Hyperventilation

Seizure disorders

Migraine

Brain tumors

Hysterical

Metabolic

Dehydration (or inadequate hydration)

Hypoglycemia

Electrolyte disorders

Anorexia nervosa

Drugs and toxins: antiseizure drugs, sedatives and tranquilizers, antihypertensive drugs.

AS, aortic stenosis; MS, mitral stenosis; MVP, mitral valve prolapse; PS, pulmonary stenosis; RV, right ventricular; SVT, supraventricular tachycardia; VT, ventricular tachycardia.

Vasovagal Syncope

Vasovagal syncope (also called simple fainting or neurocardiogenic or neurally mediated syncope) is the most common type of syncope in otherwise healthy children and adolescents. This syncope is uncommon before 10 to 12 years of age but quite prevalent in adolescent girls. It is characterized by a prodrome (warning symptoms and signs) lasting a few seconds to 1 minute; the prodrome may include dizziness, nausea, pallor, diaphoresis, palpitation, blurred vision, headache, or hyperventilation. The prodrome is followed by loss of consciousness and muscle tone. The patient usually falls without injury, the unconsciousness does not last more than 1 minute, and the patient gradually awakens. The syncope may occur after rising in the morning; after taking a morning shower; or in association with prolonged standing, anxiety or fright, pain, blood drawing or the sight of blood, fasting, hot and humid conditions, or crowded places. It may occur after prolonged exercise (if it is stopped suddenly).

The pathophysiology of vasovagal syncope is not completely understood. The following is a popular hypothesis (although dismissed by some). In normal individuals, an erect posture without movement shifts blood to the lower extremities and pelvis and causes a decrease in venous return, thus decreasing stroke volume and BP. This reduced filling of the ventricle places less stretch on the mechanoreceptor (i.e., C fibers) and causes a decrease in afferent neural output to the brain stem, reflecting hypotension. This decline in neural traffic from the mechanoreceptors and a decreased arterial pressure elicit an increase in sympathetic output, resulting in an increase in heart rate and peripheral vasoconstriction to restore BP to the normal range. Thus, the normal responses to the assumption of an upright posture are a reduced cardiac output (by 25%), an increase in heart rate, an unchanged or slightly diminished systolic pressure (Fig. 31-1), and an increase in diastolic pressure to ensure coronary artery perfusion. Cerebral blood flow decreases by approximately 6% with cerebrovascular autoregulation functioning near its maximal limit.

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FIGURE 31-1 Schematic drawing of changes in heart rate (HR) and blood pressure (BP) observed during the head-up tilt test. Thin arrows mark the start of orthostatic stress. Large unfilled arrows indicate the appearance of symptoms with changes seen in HR and BP. In normal individuals, the HR increases slightly with no change or a slight reduction in BP. In patients with vasovagal syncope, both the HR and BP drop precipitously with the appearance of symptoms. Postural hypotension is characterized by a drop in BP by 10 to 15 mm Hg as symptoms appear within 3 minutes of standing. Postural hypotension may not occur in the presence of good hydration. In POTS, the HR increases significantly by more than 30 beats/min (or the HR is 120 beats/min or higher) with development of symptoms within 10 minutes of standing. POTS, postural orthostatic tachycardia syndrome.

In susceptible individuals, however, a sudden decrease in venous return to the ventricle produces a large increase in the force of ventricular contraction; this causes activation of the left ventricular mechanoreceptors, which normally respond only to stretch (Fig. 31-2). The resulting paroxysmal increase in neural traffic to the brain stem somehow mimics the conditions seen in hypertension and thereby produces a paradoxical withdrawal of sympathetic activity and vagal activation. Withdrawal of sympathetic activity leads to a peripheral vasodilatation, hypotension, and bradycardia. Vagal activation results in bradycardia (see Fig. 31-2). Characteristically, the reduction of BP and especially the heart rate are severe enough to decrease cerebral perfusion, resulting in either presyncope or syncope (with loss of consciousness). Vasovagal syncope always occurs while the patient is in a standing position. Hypovolemia (or dehydration) is often a predisposing factor. “Stress” may also be a possible predisposing factor in the pathogenesis of syncope. With respect to the pharmacologic approach to prevent vasovagal syncope, α-adrenergic agonists, beta-blockers, serotonin reuptake inhibitors, anticholinergic muscarinic blockers, and volume expansion have been used successfully, and their presumed points of action are shown Figure 31-2.

History is most important in establishing the diagnosis of vasovagal syncope. Tilt testing of various protocols is useful in diagnosing vasovagal syncope, but it has not been well standardized, and its specificity and reproducibility are questionable.

Placing the patient in a supine position until the circulatory crisis resolves may be all that is indicated. If the patient feels the prodrome to a faint, he or she should be told to lie down with the feet raised above the chest; this usually aborts the syncope. Success in preventing syncope has been reported with medications, such as fludrocortisone (Florinef), beta-blockers, pseudoephedrine, and others (see Management section below).

Orthostatic Hypotension (Dysautonomia)

The normal response to standing is reflex arterial and venous constriction and a slight increase in heart rate. In orthostatic hypotension, the normal adrenergic vasoconstriction of the arterioles and veins in the upright position is absent or inadequate, resulting in hypotension without a reflex increase in heart rate (see Fig. 31-1). In contrast to the prodrome seen with vasovagal syncope, in orthostatic hypotension, patients experience only lightheadedness. Orthostatic hypotension is usually related to medication (see later discussion) or dehydration, but it can be precipitated by prolonged bed rest, prolonged standing, and conditions that decrease the circulating blood volume (e.g., bleeding, dehydration). Drugs that interfere with the sympathetic vasomotor response (e.g., calcium channel blockers, antihypertensive drugs, vasodilators, phenothiazines) and diuretics may exacerbate orthostatic hypotension. Dysautonomia may also be seen during an acute infectious disease or in peripheral neuropathies such as Guillain-Barré syndrome.

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FIGURE 31-2 Proposed pathophysiology of neurocardiogenic syncope. Presumed points of action of various pharmacologic agents are also shown by open arrows. LV, left ventricular. Modified from Ross BA, Saul JP: Management of vasovagal syncope: pharmacologic, nonpharmacologic, or pacing. In Walsh EP, Saul JP, Triedman JK (eds): Cardiac Arrhythmias in Children and Young Adults with Congenital Heart Disease. Philadelphia, Lippincott Williams and Wilkins, 2001.

In patients suspected of having orthostatic hypotension, BP should be measured in the supine and standing positions. The American Autonomic Society has defined orthostatic hypotension as a persistent fall in systolic/diastolic pressure of more than 20/10 mm Hg within 3 minutes of assuming the upright position without moving the arms or legs with no increase in the heart rate but without fainting. Orthostatic hypotension may only be demonstrable in the presence of dehydration. In a well-hydrated state when the individual is seen in an office setting, orthostatic hypotension may not occur. Patients with orthostatic hypotension also have a positive tilt test result but do not display the autonomic nervous system signs of vasovagal syncope, such as pallor, diaphoresis, and hyperventilation.

The same management as that given for vasovagal syncope is sometimes successful. Elastic stockings, a high-salt diet, sympathomimetic amines, and corticosteroids have been used with varying degrees of success. The patient should be told to move to an upright position slowly.

Postural Orthostatic Tachycardia Syndrome

This relatively new syndrome is a form of orthostatic intolerance that is most often observed in young women. Venous pooling associated with assuming a standing position predominantly affects the lower extremities. This leads to a reduced venous return, a resulting increase in sympathetic discharge, and a significant degree of tachycardia. An increased level of adrenomedullin, a potent vasodilator with natriuretic and diuretic effects, has been observed in some children with the syndrome, possibly as a result of endothelial dysfunction (Zhang et al, 2012).

Patients with POTS experience difficulties with daily routines such as housework, shopping, eating, attending work or school, and complaints of chronic fatigue. Children (and adults) with the syndrome often have symptoms of syncope, dizziness, chest discomfort or pain, headache, palpitation, nausea, fatigue, and exercise intolerance. This may be related to chronic fatigue syndrome and may be misdiagnosed as having panic attacks or chronic anxiety. The general physical examination is often unrevealing.

For the diagnosis of POTS, heart rate and BP are measured in the supine, sitting, and standing positions. POTS is defined as the development of orthostatic symptoms that are associated with at least a 30-beat/min increase in heart rate (or a heart rate of ≥120 beats/min) that occurs within the first 10 minutes of standing or upright tilt. An exaggerated increase in heart rate is often accompanied by hypotension in association with the symptoms described above (see Fig. 31-1). Occasional patients develop swelling of the dependent lower extremities with purplish discoloration of the dorsum of the foot and ankle. Tilt table testing is often useful as a standardized measure of response to postural change.

The same approaches of management as vasovagal syncope are used with varying level of success. One should check if any medications the patient may be taking could be contributing to the problem (e.g., vasodilators, tricyclic antidepressants, monoamine oxidase inhibitors, or alcohol). The patient is advised to avoid extreme heat and dehydration and to increase salt and fluid intake. Pharmacologic agents such as fludrocortisone, midodrine (a peripheral vasoconstrictor, at a dose of 5–10 mg three times a day), or venlafaxine (a selective serotonin reuptake inhibitor) are useful in many patients.

Exercise-Related Syncope

Sudden unconsciousness that occurs during or after strenuous physical activities or sports may signal an organic cause such as cardiopulmonary diseases, including cardiac arrhythmia. However, in most cases, exercise-related syncope is not an indicator of serious underlying cardiopulmonary or metabolic disease. It occurs more often because of a combination of venous pooling in vasodilated leg muscles, inadequate hydration, and high ambient temperature. Hyperventilation with hypocapnia (with tingling or numbness of extremities) secondary to strenuous activities may also cause syncope. To prevent venous pooling, athletes should keep moving after running competitions.

Rare Causes of Syncope

Micturition syncope is a rare form of orthostatic hypotension. In this condition, rapid bladder decompression results in decreased total peripheral vascular resistance with splanchnic stasis and reduced venous return to the heart, resulting in postural hypotension.

Cough syncope occurs after paroxysmal nocturnal coughing in children with asthma. The patient’s face become plethoric and cyanotic, and the child perspires, becomes agitated, and is frightened. Loss of consciousness is associated with muscle contractions lasting for several seconds. Urinary incontinence is frequent. Consciousness is regained within a few minutes. Paroxysmal coughing produces a marked increase in intrapleural pressure with a reduced venous return and reduced cardiac output, resulting in altered cerebral blood flow and loss of consciousness. Treatment is aimed at preventing bronchoconstriction with aggressive asthma treatment plans

Cardiac Causes of Syncope

Cardiac causes of syncope may include obstructive lesions; myocardial dysfunction; and arrhythmias, including long QT syndrome and Brugada syndrome. A cardiac cause of syncope is suggested by the occurrence of syncope even in the recumbent position, syncope provoked by exercise, chest pain associated with syncope, a history of unoperated or operated heart disease, or a family history of sudden death.

Obstructive Lesions

Patients with severe obstructive lesions, such as aortic stenosis (AS), pulmonary stenosis (PS), or hypertrophic obstructive cardiomyopathy (HOCM), as well as those with pulmonary hypertension, may have syncope. Exercise often precipitates syncope associated with these conditions. Peripheral vasodilatation secondary to exercise is not accompanied by an adequate increase in cardiac output because of the obstructive lesion, which results in diminished perfusion to the brain. Patients may also complain of chest pain, dyspnea, and palpitation.

Myocardial Dysfunction

Although rare, myocardial ischemia or infarction secondary to congenital anomalies of the coronary arteries or acquired disease of the coronary arteries (e.g., Kawasaki’s disease or atherosclerotic heart disease) may cause syncope. Patients with dilated cardiomyopathy may have episodes of syncope associated with self-terminating episodes of ventricular tachycardia, which can lead to cardiac arrest. Syncope is a major risk factor for subsequent sudden cardiac death in hypertrophic cardiomyopathy, particularly if it is repetitive and occurs with exertion. Arrhythmogenic RV dysplasia often develops ventricular tachycardia caused by myocyte replacement by adipose tissue or fibrosis.

Arrhythmias

Either extreme tachycardia or bradycardia can decrease cardiac output and lower the cerebral blood flow below the critical level, causing syncope. The occurrence of syncope in the sitting or recumbent position suggests cardiac arrhythmias (or seizure) as the cause of syncope. Commonly encountered rhythm disturbances include supraventricular tachycardia (SVT), ventricular tachycardia, sick sinus syndrome, and complete heart block. Simple bradycardia is usually well tolerated in children, but the combination of tachycardia followed by bradycardia (overdrive suppression) is more likely to produce syncope. Arrhythmias may or may not be associated with structural heart defects.

No identifiable structural defects. Syncope from arrhythmias in children with structurally normal hearts may be seen in the following conditions.

1. Long QT syndrome is characterized by syncope caused by ventricular arrhythmias, prolongation of the QT interval on the electrocardiogram (ECG), and occasionally a family history of sudden death. Congenital deafness is also a component of Jervell and Lange-Nielsen syndrome but not of Romano-Ward syndrome.

2. Short QT syndrome.

3. Wolff-Parkinson-White (WPW) preexcitation may cause SVT.

4. Right ventricular (RV) dysplasia (RV cardiomyopathy) is a rare anomaly of the myocardium and is associated with repeated episodes of ventricular tachycardia (see Chapter 18).

5. Brugada syndrome is a rare cause of sudden death by ventricular arrhythmias, seen mostly in the Southeast Asian men. Syncope typically occurs at rest (90%). The ECG typically shows right bundle branch block with J-point elevation and concave ST elevation in V1.

Structural heart defects. The following congenital and acquired heart conditions, unoperated or operated, are associated with arrhythmias that may result in syncope.

1. Preoperative congenital heart defects (CHDs), such as Ebstein’s anomaly, mitral stenosis (MS), and mitral regurgitation (MR), and congenitally corrected transposition of the great arteries (L-TGA), may cause arrhythmias.

2. Postoperative CHDs may cause arrhythmias, especially after repairs of tetralogy of Fallot (TOF) and transposition of the great arteries (TGA) and after the Fontan operation. These children may have sinus node dysfunction (sick sinus syndrome), SVT or ventricular tachycardia, or complete heart block.

3. Dilated cardiomyopathy can cause sinus bradycardia, SVT, or ventricular tachycardia.

4. Hypertrophic cardiomyopathy is a rare cause of ventricular tachycardia and syncope.

5. Mitral valve prolapse (MVP) is an extremely rare cause of ventricular tachycardia.

Evaluation of a Child with Syncope

Most children who present with presyncope (without loss of consciousness) or even syncope have vasovagal phenomena or other benign causes of syncope. However, the goal of the evaluation of a patient with syncope (or presyncope) is to identify high-risk patients with underlying heart disease, which may include ECG abnormalities (such as seen in long QT syndrome, WPW preexcitation, Brugada syndrome), cardiomyopathy (hypertrophic or dilated), or structural heart diseases. The evaluation of pediatric patients with syncope may extend to other family members when a genetic condition is suspected or identified.

History

Because physical examinations of patients are almost always normal long after the event, accurate history taking is most important in determining a cost-effective diagnostic workup for each patient. Sometimes a complete history cannot be obtained owing to amnesia about the event, but witness accounts are useful. The following are some important aspects of history taking.

1. About the syncopal event

a. The time of the day

• Syncope occurring after rising in the morning or after morning shower suggests vasovagal syncope.

• Hypoglycemia is a very rare cause of syncope, occurring in a fasting state in the morning.

b. The patient’s position (supine, standing, or sitting)

• Syncope while sitting or recumbent suggests arrhythmias or seizures.

• Syncope after standing for some time suggests orthostatic intolerance group, including vasovagal syncope.

c. Relationship to exercise

• Syncope occurring during exercise suggests arrhythmias.

• Syncope occurring immediately after cessation of physical activities suggests venous pooling in the leg (with reduced venous return and cardiac output).

• Estimating vigorousness and duration of the activity, relative hydration status, and ambient temperature at the time of syncope is important.

d. Associated symptoms sometimes are helpful in suspecting the cause of syncope.

• Palpitation or a racing heart rate suggests tachycardia or arrhythmias.

• Chest pain suggest possible myocardial ischemia (e.g., obstructive lesions, cardiomyopathy, carditis).

• Shortness of breath or tingling or numbness of the extremities suggests hyperventilation.

• Nausea, epigastric discomfort, and diaphoresis suggest vasovagal syncope.

• Headache or visual changes suggest vasovagal syncope.

e. The duration of syncope

• A syncopal duration less than 1 min suggests vasovagal syncope, postural hypotension, or hyperventilation.

• A longer duration of syncope suggests convulsive disorders, migraine, or arrhythmias.

f. The patient’s appearance during and immediately after the episode

• Pallor indicates hypotension.

• Abnormal movement or posturing, confusion, focal neurologic signs, amnesia, or muscle soreness suggests the possibility of seizure.

2. History of a cardiac, endocrine, neurologic, or psychological disorders may suggest a disorder in that system.

3. Medication history, including prescribed, over-the-counter, and recreational drugs, should be checked.

4. Family history should include:

a. Coronary heart disease risk factors, including history of myocardial infarction in family members younger than 30 years of age

b. Cardiac arrhythmia, CHD, cardiomyopathies, long QT syndrome, seizures, metabolic and psychological disorders

c. A positive family history of fainting is common in patients with vasovagal syncope.

5. Social history is important in assessing whether there is a possibility of substance abuse, pregnancy, or factors leading to a conversion reaction.

Physical Examination

Although the results of the physical examination are usually normal, a complete physical examination should always be performed, focusing on the patient’s cardiac and neurologic status.

1. If orthostatic intolerance group is suspected, the heart rate and BP should be measured repeatedly while the patient is supine and after standing without moving for up to 10 minutes. In a well-hydrated state, positive test results for vasovagal syncope or postural hypotension in the office setting are uncommon.

2. Careful auscultation is carried out to detect a heart murmur or an abnormally loud second heart sound.

3. Neurologic examination should include a funduscopic examination, test for Romberg’s sign, gait evaluation, test of deep tendon reflexes, and test of cerebellar function.

Diagnostic Studies

History and physical examinations guide practitioners in choosing the diagnostic tests that apply to a given patient with syncope. A complete cardiac evaluation is indicated if there is a heart murmur, a family history of sudden death or cardiomyopathy, or an abnormal ECG finding.

1. Serum glucose and electrolytes is of limited value because the patients are seen hours or days after the episode.

2. In suspected cases of arrhythmia as the cause of syncope, the following may be indicated.

a. ECG: All patients presenting with syncope should have an ECG. The ECG should be inspected for heart rate (bradycardia), arrhythmias, WPW preexcitation, heart block, and long QTc interval, as well as abnormalities suggestive of cardiomyopathies and myocarditis.

b. Ambulatory ECG monitoring: A correlation between the patient’s symptoms and a diagnostic arrhythmia confirms the arrhythmic cause of syncope. Symptoms without arrhythmia probably exclude an arrhythmic cause of syncope.

(1) A Holter monitor usually records ECG for up to 24 hours.

(2) Loop memory event recorders with extended monitoring (usually for 1 month) may increase the diagnostic yield.

(3) A nonlooping event recorder can be used for symptoms lasting for a few minutes (usually for a month).

(4) An implantable loop recorder (implanted in the left pectoral region) is a device that can be used to record ECGs for a period much longer than 1 month.

c. Exercise stress test: If the syncopal event is associated with exercise, a treadmill exercise stress test should also be performed with full ECG and BP monitoring (see Chapter 6, Noninvasive Techniques).

3. Echocardiographic studies: These studies identify structural abnormalities that can cause of syncope and chest pain. Identifiable structural causes include severe obstructive lesions (e.g., AS, PS, HOCM), pulmonary hypertension, certain CHDs (Ebstein’s anomaly, mitral stenosis or regurgitation, L-TGA), and the status of postoperative CHDs (e.g., TOF, TGA, Fontan operation).

4. Head-up tilt table test: If patients with syncope have autonomic symptoms (e.g., pallor, diaphoresis, or hyperventilation), tilt table testing is useful (see subsequent section for full discussion).

5. Cardiac catheterization and electrophysiologic testing may rarely be indicated in some equivocal cases. Because of the low yield of electrophysiologic testing in patients without underlying heart disease, this test is not routinely recommended in such cases.

6. Neurologic consultation: Patients exhibiting prolonged loss of consciousness, seizure activity, and a postictal phase with lethargy or confusion should be referred for neurologic consultation and electroencephalography. Without the above history, the reported positive yield of electroencephalography or imaging studies is very low.

Head-up tilt table test: The goal of tilt table testing is to provoke the patient’s symptoms exactly during orthostatic stress while being closely monitored, with demonstration of the cardiac rhythm and rate and BP responses associated with symptoms. Orthostatic stress is created by a tilting table with the patient placed in an upright position to obtain the necessary pooling of blood to the lower extremities.

Patients lie supine on an electric tilt table and have an intravenous line established. ECG monitoring and automated BP measurements are performed. Some laboratories perform autonomic challenge test, which includes deep breathing to accentuate sinus arrhythmia, carotid massage (not done in adults, especially elderly adults), Valsalva maneuver, and the application of ice to the face to induce the “diving reflex.” Patients are then tilted into the 60- to 80-degree head-up position for a period of up to 30 minutes. These patients remain upright, with recording of BP every 1 or 2 minutes and continuous heart rate and rhythm monitoring. If a patient becomes symptomatic or the 30-minute time elapses, the tilt table is immediately returned to the supine position. If the tilt test alone result is not positive, the procedure is repeated with an infusion of isoproterenol, starting at 0.02 μg/kg per minute and increasing to 1 μg/kg per minute for 15 minutes. The use of isoproterenol in the evaluation of patients with vasovagal syncope remains somewhat controversial. Some believe that responses to isoproterenol are nonspecific.

Positive responses commonly include lightheadedness, dizziness, nausea, visual changes, and frank syncope. Sinus bradycardia, junctional bradycardia, and asystole for as long as 30 seconds are common. Hypotension generally is manifested by systolic BPs of less than 70 mm Hg, with frequently immeasurable diastolic BPs. Returning these patients to the supine position produces resolution of symptoms rapidly, with a return of normal sinus rhythm, usually with a reactive tachycardia. Patients frequently comment that they “had a spell” and that they feel tired and weak.

Several distinct abnormal patterns have been identified after head-up tilt table tests (see Fig. 31-1).

1. Vasovagal: An abrupt decrease in BP usually with bradycardia

2. Dysautonomia (or postural hypotension): A gradual decrease in BP leading to syncope

3. POTS: An excessive heart rate increase to maintain an adequate BP to prevent syncope

After a positive tilt test result, many laboratories begin a therapeutic trial of a short-acting beta-blocker, such as an esmolol infusion, and repeat the tilt test. If the patient does not become symptomatic during the tilt test, an oral beta-blocker is prescribed (see subsequent discussion). If the patient is again symptomatic, he or she is tested with infusion of an α-agonist (phenylephrine) with a repeat tilt table test. Finally, the patient is tested with a bolus of 1 L of normal saline. If the patient remains asymptomatic during the test, the patient is treated with volume expansion therapy using a mineralocorticoid (Florinef) and salt supplementation (see later discussion).

There are, however, serious questions about the sensitivity, specificity, diagnostic yield, and day-to-day reproducibility of the tilt test. In adults, the overall reproducibility of syncope by the tilt test is disappointingly low (62%), which causes doubt about the specificity of the test for diagnosis and the validity of evaluating the effect of oral drug treatment by a repeat tilt test. About 25% of adolescents with no prior fainting history fainted during the tilt test. Moreover, among habitual fainters, 25% to 30% did not faint during the test on a given day.

Treatment

The same preventive measures are used for all orthostatic intolerance group of conditions. Beginning the therapy empirically without performing a head-up tilt table test is not unreasonable. Most patients show spontaneous resolution of syncope in 6 to 12 months; therefore, long-term medical prophylaxis is usually not necessary.

Orthostatic Intolerance Syndromes (including vasovagal syndrome)

1. Maintaining adequate intravascular volume is the most important element in the prevention of syncope.

a. The patient is recommended to drink 60 to 90 oz of water a day. Physical activities, especially in a hot environment, require much more fluid intake, preferably electrolyte-containing fluids (e.g., Gatorade).

b. Drinking “sport drinks” with additional sodium is an option.

c. Liberal use of salt with meals and nonfatty salted snacks (e.g., pretzels, popcorn without butter) are recommended.

d. Caffeinated beverages should be avoided (because of their renal diuretic effect).

e. Wearing elastic support hose (waist high) is useful in some patients with postural hypotension.

2. Success in preventing syncope has been reported with the following medications. Their mechanism of action is shown in Figure 31-2.

a. Fludrocortisone (Florinef), a mineralocorticoid, increases intravascular volume and also produces both venous and arterial vasoconstriction. It can be given in a low dosage (0.1 mg by mouth once or twice a day; adult dose ≈0.2 mg/day) with increased salt intake or a salt tablet (1 g daily). Average preadolescents or adolescents commonly gain 1 or 2 kg of water weight into their circulating volume within 2 or 3 weeks. The increased vascular volume allows these patients to maintain cerebral BP despite the normal episodic parasympathetic-mediated venodilatation.

b. Beta-blocker therapy is used commonly, especially in adolescents and young adults, to modify the feedback loop. Atenolol (1–1.2 mg/kg/day orally every day; maximum dose, 2 mg/kg/day) and metoprolol (1.5 mg/kg/day given orally in two or three doses) are most commonly used.

c. α-Agonist therapy using pseudoephedrine or an ephedrine–theophylline combination (Marax) stimulates the heart rate and increases the peripheral vascular tone, preventing reflex bradycardia and vasodilation. Pseudoephedrine, 60 mg, given orally twice a day, has been reported to be beneficial in some older children and adolescents.

3. Less commonly used medications include:

a. Disopyramide 150 mg three times a day orally has been reported to be effective in mostly adult patients with severe cases of vasovagal syncope. Disopyramide may owe its beneficial effects to its negative inotropic properties, vasoconstricting action, and anticholinergic action.

b. The efficacy of serotonin agonists (sertraline [Zoloft]) has also been described in the treatment of patients with refractory syncope.

4. Cardiac Pacemaker. Beneficial effects of an implanted pacemaker for vasovagal syncope have been reported by some investigators but not by others. It is generally not indicated in pediatric patients. In a recent double-blind, randomized trial in adult patients, recurrent syncope still occurred; even though the pacemaker maintained the heart rate, BP dropped, and symptoms still occurred (Connolly et al, 2003).

Cardiac Arrhythmias

Patients with primary cardiac arrhythmias presenting as syncopal events may require antiarrhythmic medications. Most arrhythmias respond to antiarrhythmic therapy. Patients with long QT syndrome are treated with beta-blockers, pacemakers, or implantable cardioverter-defibrillators (see Chapter 24). Propranolol or other antiarrhythmic drugs may be indicated in patients with symptomatic MVP syndrome. Occasionally, catheter ablation may be indicated in some patients (e.g., in patients with WPW syndrome causing frequent SVT).

Differential Diagnosis

A thorough history taking usually directs the physician to the correct diagnosis and thereby reduces the number of unnecessary tests.

Epilepsy. Patients with epilepsy may have incontinence, marked confusion in the postictal state, and abnormal electroencephalograms. Patients are rigid rather than limp and may have sustained injuries. Patients do not experience the prodromal symptoms of syncope (e.g., dizziness, pallor, palpitation, diaphoresis). The duration of unconsciousness is longer than that typically seen with syncope (<1 minute).

Hypoglycemia. Hypoglycemia has characteristics similar to syncope, such as pallor, perspiration, abdominal discomfort, lightheadedness, confusion, unconsciousness, and possible subsequent occurrence of seizures. However, hypoglycemic attacks differ from syncope in that the onset and recovery occur more gradually, they do not occur during or shortly after meals, and the presyncopal symptoms do not improve in the supine position.

Hyperventilation. Hyperventilation is believed to produce hypocapnia, resulting in intense cerebral vasoconstriction, and causes syncope. A recent study, however, demonstrates that hyperventilation alone is not sufficient to cause syncope, suggesting that it may also have a psychological component. A typical spell usually begins with an apprehensive feeling and “deep sighing respirations” that the patient rarely notices. The patient often experiences air hunger, shortness of breath, chest tightness, abdominal discomfort, palpitations, dizziness, numbness or tingling of the face and extremities, and rarely loss of consciousness. It often is associated with emotional disturbances. The supine position may help the patient relax and may stop the anxiety–hyperventilation cycle. The syncopal episode can be reproduced in the office when the patient hyperventilates.

Hysteria. Syncope resulting from hysteria is not associated with injury and occurs only in the presence of an audience. A teenager may be able to give an accurate presyncopal history, but during these attacks, he or she does not experience the pallor and hypotension that characterize true syncope. The attacks may last longer (up to 1 hour) than a brief syncopal spell. Episodes usually occur in an emotionally charged setting and are rare before 10 years of age. Spells are not consistently related to postural changes and are not improved by the supine position.