Chapter 51: Syncope

• Most syncope in children is neurocardiogenic/vasovagal.

• Situational events that cause a Valsalva-like maneuver can cause syncope.

• Prolonged QT syndrome is an uncommon but important cause of syncope in children.

• A head upright tilt-table test may diagnose neurocardiogenic syncope in selected cases.

Syncope refers to a sudden, brief loss of consciousness and postural tone. Although in the pediatric age group it accounts for less than 1% of emergency department visits, 15% to 50% of children will have experienced a syncopal episode by age 18 years.¹ The etiology of syncope in children is generally benign. Syncope can, however, be a manifestation of serious underlying pathology and always warrants careful evaluation. Unlike the adult population, in which syncope often results from malignant cardiac arrhythmias, in the pediatric population it is more often secondary to neurally mediated causes and is therefore discussed in the section on neurologic emergencies.¹ An extensive workup for syncope is usually unnecessary. All children presenting to the ED with syncope should have a detailed history, physical examination, and electrocardiogram (ECG) performed.

The pathophysiology of syncope varies with etiology (Table 51-1), but it always results from momentarily inadequate delivery of oxygen and glucose to the brain. Syncope can result from dangerous causes such as inadequate cardiac output, which can be secondary to obstruction of blood flow, or to an arrhythmia. It can also result from more benign events such as inappropriate autonomic compensation for the normal fall in blood pressure that occurs on rising from a sitting or supine position. Metabolic causes such as hypoglycemia should also be considered especially in at-risk patients (e.g., diabetes). Respiratory disturbances, especially hyperventilation that results in hypocapnia and cerebral vasoconstriction, can also cause syncope.¹

The first component in the evaluation of a patient with syncope is to determine that momentary loss of consciousness actually occurred. It is common for patients to confuse acute dizziness or vertigo with loss of consciousness. With a good history, it is often discovered that many patients had a near-syncopal event versus true syncope. It is unclear whether this should impact the workup. For patients who did indeed lose consciousness, the events antecedent to the syncopal episode are elicited. A prodrome of light-headedness, nausea, dizziness or vision changes, a sudden change in posture, emotional excitement, respiratory difficulty, palpitations, exercise, and any history of trauma are essential information. An association with exertion, palpitations, chest pain, and shortness of breath should be queried as this increases one's suspicion for a cardiac etiology. Past history of syncope is sought, as is any history of medication or drug ingestion that would explain a precipitous fall in blood pressure. Patients are queried carefully about any history of congenital heart disease, any family history of heart disease, or family history of sudden death in children or young adults.^2,3 Medical conditions that put patients at risk for metabolic derangement, such as diabetes mellitus or insipdus, should also be sought.

An important consideration in any patient with a history of loss of consciousness is the possibility that the patient may have suffered a seizure. In contrast to syncope, seizures are usually accompanied by some form of muscle twitching or convulsions, and are usually followed by a postictal phase, during which the patient has confusion, disorientation, or other mental status changes, usually lasting more than 5 minutes.⁴ Convulsions are unusual during syncopal episodes except during very severe events, or with reflex anoxic seizures, and patients generally have normal mental status upon recovery from the episode.^2,5

The physical examination focuses upon establishing the hemodynamic stability of the patient. Particular attention is paid to vital signs, especially to pulse and orthostatic blood pressure. A positive test is a decrease in systolic blood pressure by 20 mm Hg or an increase in heart rate (20 beats per minute [bpm]), ongoing from lying to sitting, or sitting to standing. However, if the patient has recurrent symptoms, the test is considered positive.⁶

For all patients, a careful cardiac examination is indicated. The regularity of the pulse is noted, as is the quality of the peripheral pulses. The heart is auscultated carefully to detect the presence of a murmur that may indicate congenital heart disease, especially aortic stenosis (systolic ejection murmur and ejection click). The presence of gallops, rubs, thrills, or carotid bruits is noted. The quality and presence of all peripheral pulses are evaluated. Diminished pulses should prompt blood pressure measurements in all extremities to check for coarctation of the aorta.⁶

The patient's mental status is carefully evaluated, and an age-appropriate neurologic examination is performed. Any abnormalities should be noted and considered for further evaluation.

The selection of laboratory studies of use in the evaluation of the syncope patient is largely guided by the history and physical examination (Fig. 51-1). For a patient with a history of fasting or diabetes, the measurement of blood glucose is indicated. In the presence of pallor or a history of blood loss, hemoglobin measurement is obtained. Electrolyte abnormalities are uncommon, but if an arrhythmia is suspected, then serum potassium, calcium, and magnesium are measured. Other studies including arterial blood gas, toxicology screening, and pregnancy testing may be indicated in certain clinical scenarios.⁶

For all patients with a history of syncope, a 12-lead ECG is indicated. This provides information concerning potential conduction defects or arrhythmias. Special attention is paid to determination of the corrected QT interval (QT_c), since prolonged QT syndromes as well as a short QT_c are causes of syncope in children. Other abnormalities to note include bradyarrhythmias, AV block, delta waves (preexcitation/Wolff–Parkinson–White [WPW]), epsilon waves (ARVD), and ST segment elevation in V₁–V₃ (Brugada syndrome), and left ventricular hypertrophy or strain patterns (hypertrophic cardiomyopathy). If abnormalities are seen, or if a cardiac abnormality is strongly suspected, further evaluation will include a 24-hour ambulatory (Holter) monitor or continuous loop event monitoring and cardiology consultation.^4,6

Other studies are dependent upon the suspected etiology. If the event is thought to be a seizure, rather than syncope, an EEG is appropriate. The head upright tilt-table test helps confirm the diagnosis of neurocardiogenic syncope, but is often reserved for those with recurrent unexplained syncope or presyncope, syncope resulting in injury, or exercise-induced syncope.³

Neurocardiogenic (Autonomic, Vasodepressor, Vasovagal) Syncope

The most common syncope in children is neurocardiogenic (vasodepressor or vasovagal) syncope. There is a sudden, brief loss of consciousness because of vasodilatation and decreased peripheral resistance, resulting in decreased arterial pressure, hypotension, bradycardia, and then decreased cerebral blood flow (Bezold–Jarisch reflex). Often times this occurs in response to postural changes, pain, or emotional stress. Current theories suggest that the systemic vasodilation and the changes in heart rate and blood pressure are caused by sympathetic withdrawal, rather than increased parasympathetic (vagal) activity.¹ Orthostatic hypotension may be a result of volume depletion, anemia, or drugs, but it can also be because of a paradoxic response to the vasodepressor reaction.^4,6 A tilt-table test can be performed by a cardiologist to diagnose true neurocardiogenic syncope. A positive head upright tilt-table test response, consisting of an initial increase in heart rate followed by bradycardia and syncope, may warrant drug therapy if frequent episodes occur.¹

Environmental factors, such as prolonged standing, heat, fatigue, crowding, or hunger, can trigger syncope. Emotional stress or a recent illness can also play a role. Patients may have symptoms beforehand such as blurred vision, dizziness, nausea, or pallor. This is what is commonly referred to as a “simple faint.” Placing the person in a supine position with the head down usually results in improvement, although the patient may still complain of dizziness.⁶

The term situational syncope can be used for those patients that have syncope triggered by specific events. The common denominator is that these actions are accompanied by a Valsalva-like maneuver. This includes coughing, micturition, hairgrooming, diving, weight lifting, and sneezing. Another form is carotid sinus syncope, which occurs with head rotation or pressure on the carotid sinus. This can occur with shaving or tight collars.¹

Breath-holding spells are another example of reflex syncope. The age of onset of breath-holding spells is 6 to 18 months.⁵ The two types of breath-holding spells are classified on the basis of the color change.

• The pallid breath-holding spell is a form of reflex syncope. Pallid breath-holding spells are usually provoked by some mild antecedent trauma (usually to the head), pain, or fright. The child may gasp and cry, then become quiet, lose postural tone and consciousness, and become pale. The child may have clonic movements and incontinence in more severe episodes. The child regains consciousness in less than 1 minute, but may be tired after the episode for several hours.⁵

• A cyanotic breath-holding spell is often precipitated by anger or frustration. The child cries, becomes quiet, and holds the breath in expiration. This apnea is associated with cyanosis and there may be a loss of consciousness, limpness, or opisthotonic posturing, with recovery usually within 1 minute.⁵

Orthostatic Intolerance and Postural Orthostatic Tachycardia Syndrome

Both these syndromes are based on symptomatic, excessive orthostatic rise in heart rate when going from lying to standing positions. For a diagnosis of orthostatic intolerance (OI), an elevation of HR of at least 30 bpm is required within 5 minutes of active standing. Postural orthostatic tachycardia syndrome (POTS) is characterized by an elevation of heart rate of at least 30 bpm and an absolute heart rate >120 within 10 minutes of head up tilt without a significant decline in BP.⁷ A recent consensus statement states that for kids and teens (12–19 years), an elevation of 40 bpm is required.^8,9 It appears to be most prevalent in females (80%) and is likely acquired, possibly from a viral illness.¹⁰ Symptoms typically occur when the patient stands up or have been standing for a prolonged period of time (5–30 minutes). Common symptoms include tachycardia, lightheadedness, blurred vision, tremulousness, headache, and fatigue.¹¹ For a diagnosis of POTS, the symptoms must be ongoing for 6 months (Table 51-2). The etiology is unclear but is thought to involve some sort of central hypovolemia and possible cerebral blood flow dysregulation given the absence of orthostatic hypotension. Symptoms may present in adolescence within 1 to 3 years of their growth spurt. This syndrome can often be debilitating and is associated with chronic fatigue syndrome. A multidisciplinary approach to treatment is generally warranted. Treatments include volume expansion with increased fluids and salt, increased aerobic exercise, and at times pharmacologic therapies.

Cardiac Syncope

Cardiac syncope is important to exclude, as this is the type that is truly life-threatening. The differential in this subgroup includes arrhythmia, obstruction, cyanosis, and other cardiac etiologies. Arrhythmias that result in a heart rate that is too fast or too slow can cause a decrease in cardiac output and lead to decreased cerebral perfusion. Included in this group are supraventricular tachycardia (SVT), atrial tachycardia, WPW syndrome, atrial flutter, ventricular tachycardia, and ventricular fibrillation. Conduction abnormalities such as AV block, sick sinus syndrome (may occur after cardiac surgery), long QT syndrome, congenital short QT, or Brugada syndrome may be present.

Long QT Syndrome

Long QT syndrome is a disorder of myocardial repolarization that can lead to polymorphic ventricular tachycardia (torsades de pointes) (Fig. 51-2). There are congenital forms: Romano–Ward syndrome (autosomal dominant), and Jervell and Lange–Nielsen syndrome (autosomal recessive). The latter form is associated with sensioneural deafness. There are also acquired forms, usually the result of the metabolic disorders such as hypokalemia and hypomagnesemia, some medications (quinidine, procainamide), or a combination of medications (erythromycin or ketoconazole and terfenadine).⁶ Although prolongation of the corrected QT_c is the main requirement, this value changes with the patient's age and sex (QT_c is >450 ms in males and >460 ms in females).¹² To calculate the QT_c, use Bazett's formula: QT_c = QT/√RR (where RR is the RR interval).² After evaluation by a cardiologist, treatments include β-blockers, implantable defibrillators, and avoidance of medication that prolong the QT interval.¹³

Congenital Short QT Syndrome

This syndrome has led to sudden cardiac death, syncope, and atrial fibrillation. The QT_c is ≤0.30 ms.²

Brugada Syndrome

Patients with this inherited autosomal dominant disorder have a characteristic ECG pattern: ST segment elevation (≥2 mm) in leads V₁–V₃. There is an increased risk of sudden cardiac death resulting from polymorphic ventricular tachyarrhythmias.^14,15 Although it is more likely to occur in young males, with a reported mean age of sudden death at 40 years, children have been detected with this disorder during family screening, and there was no male predominance, and febrile illness was the most important precipitating event.¹⁴

Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD) is characterized by ventricular tachycardia and abnormalities of the right ventricle, caused by myocyte replacement by fibrosis or adipose tissue. Although sudden cardiac death may be the presenting feature (mean age of 30 years), premature ventricular contractions (PVCs), syncope, and ventricular tachycardia with left bundle branch block may be forewarning findings. Diagnosis is based on ECG findings (epsilon waves after the QRS) as well as structural and functional criteria.^2,6,16

All these problems should be excluded by evaluation of a 12-lead ECG and rhythm strip. If the problem is intermittent, 24-hour Holter monitoring and referral to a cardiologist should be included in the evaluation.

Obstructive lesions can impair cardiac output and cerebral blood flow leading to syncope. These include congenital lesions such as aortic stenosis, pulmonic stenosis, idiopathic hypertrophic subaortic stenosis (IHSS), hypertrophic cardiomyopathy, mitral stenosis, coarctation of the aorta, tetralogy of Fallot, anomalous origin of the left coronary artery, and transposition of the great vessels. Children who have undergone surgical correction of tetralogy, transposition, and aortic stenosis are at greater risk of arrhythmias.² The presence of chest pain and syncope with exercise, as well as a murmur on physical examination, can suggest left ventricular outflow obstruction because of IHSS or aortic stenosis. Cyanosis with or without syncope can result from increased resistance to pulmonary blood flow, causing an increase in the right-to-left shunting of blood. These spells can occur in children with tetralogy of Fallot, tricuspid atresia, and Eisenmenger's syndrome.

Evaluation for these disorders includes an ECG, chest radiograph, echocardiogram, and cardiology consultation.²

Hypertrophic Cardiomyopathy

This autosomal dominant disorder is characterized by asymmetric hypertrophy of the left ventricle, without dilatation. It is a common cause of sudden death associated with exercise in young patients. Syncope is a major risk factor for sudden death. The mechanisms that cause syncope and sudden death include bradyarrhythmias, ventricular arrhythmias, severe outflow tract obstruction, and decreased blood pressure in response to exercise.^2,13 Implantable defibrillators have been used to treat this disorder with some success.¹³

Acquired lesions include cardiac tumors and conditions secondary to myocarditis, pericarditis, cardiac tamponade, cardiomyopathy, and pulmonary hypertension. Primary pulmonary hypertension can cause dyspnea on exertion but can also cause syncope from inadequate cardiac output. Evaluation includes a 12-lead ECG, chest radiograph, and prompt cardiology referral.²

Noncardiac Syncope

Noncardiac causes of syncope include neurologic, metabolic, psychologic, and toxicologic problems. Seizures should be considered whenever there is a loss of consciousness, especially if accompanied by increased muscle tone or tonic–clonic movements. If syncope occurs while the child is in a recumbent position, a seizure is a likely diagnosis. The diagnostic workup should proceed based on the most likely etiology and type of seizure.²

Hypoglycemia is the main metabolic disorder that can cause syncope. Prior to a loss of consciousness, there is often a period of confusion and weakness. The patient may also become diaphoretic. Hypocalcemia and hypomagnesemia can also cause syncope, but this is secondary to the arrhythmias generated by these disorders.

Psychologic causes of syncope include hyperventilation and hysteria. Hyperventilation results in hypocapnia, which causes cerebral vasoconstriction and decreased cerebral blood flow. The patient may complain of shortness of breath, chest tightness, numb fingers and lips before syncope ensues.¹ Hysteric syncope occurs when the patient mimics a loss of consciousness and falls to the ground without injury. No abnormalities of heart rate, blood pressure, or skin color are detected, and clues regarding surrounding events may point to the correct diagnosis, such as prolonged recovery after the event, and indifference to syncope.^2,3 Depressive symptomatology is often found in patients with neurocardiogenic syncope. The pathophysiologic association is unclear.¹⁷

Prescription drugs, over-the-counter medications, or drugs of abuse can cause drug-induced syncope. Drugs of abuse such as cocaine are well known to result in syncope as well as more serious cardiac arrhythmias. Marijuana, alcohol, and opiates can all cause a loss of consciousness.^1,2 Inhalant use can result in ventricular tachycardia and death. Antihypertensive agents, phenothiazines, calcium-channel blockers, nitrates, and barbiturates can block the increased blood pressure response, and β-blockers and digitalis will block the tachycardia needed to respond to decreased systemic vascular resistance prior to syncope. Some of the newer antihistamines can cause prolonged QT and even torsades de pointes, if given with macrolides or ketoconazole.¹

Although most children will not require specific therapy, treatment should be based on the etiology and frequency of syncopal episodes. A child with hypoglycemia requires glucose, and one with anemia or hypotension may benefit from intravenous fluids while a workup for the etiology is ongoing. If a cardiac etiology is suspected, depending on the urgency of the situation, further studies could be performed on an inpatient or outpatient basis, but activity restrictions may be needed while awaiting evaluation. Treatment of a child with orthostatic syncope with β-blockers or mineralocorticoids should await formal head upright tilt-table testing. If a neurologic etiology is suspected, treatment with anticonvulsive medications should be based on neurologic consultation. If the emergency department evaluation and workup is negative, with the likely etiology being neurocardiogenic, or a simple faint, reassurance may be all that is needed. Avoidance of specific triggers or environmental factors can prevent most attacks. Those with a prodromal phase can be taught to sit or lie down before the loss of tone and consciousness occurs.

Disposition

Most patients with syncope can be discharged from the emergency department with appropriate follow-up. Those who require admission have conditions with a cardiac origin that require urgent evaluation: arrhythmias (SVT, atrial flutter, ventricular tachycardia, or fibrillation), conduction abnormalities (third-degree AV block, sick sinus syndrome), or newly diagnosed or worsening of obstructive lesions (aortic stenosis, pulmonic stenosis, IHSS).⁶ Patients with arrhythmias precipitated by drugs require inpatient monitoring, for at least the half-life of the offending agent. Patients in whom a cardiac etiology is suspected should refrain from athletics or any exertional activity until cleared by a cardiologist. Patients with cyanosis with syncope, those with abnormal neurologic examinations, and those with orthostatic syncope who do not resolve with fluids, and have no other etiology should also be admitted.⁶