Syncope is the sudden and transient loss of conscious-ness and postural tone that results from inadequate cere-bral perfusion. Syncope in children causes great anxiety in parents, teachers, and school officials. These episodes result in a large number of visits to pediatricians, family physicians, and emergency departments and a surprising number of admissions to community and children’s hos-pitals nationwide.15 Although children may require some cardiac testing, they rarely require the complete cardiovascular assessment that older adults with the same presentation routinely receive, which often culmi-nates in coronary angiography and electrophysiologic testing. The greatest concern regarding syncope is to discern which children might be at risk for sudden car-diac death. The overall incidence of sudden death in children and teenagers is 1–8 in 100,000 patient-years.16 Some particular features should prompt a more aggres-sive emergent evaluation, such as syncope with exertion or syncope associated with cardiac symptoms such as chest pain or palpitations; prolonged or frequent syn-cope; syncope associated with known, preexisting con-genital or acquired heart disease; syncope requiring cardiopulmonary resuscitation (CPR) or in patients with known arrhythmia such as LQTS; or a family history of sudden death.
Epidemiology
The reported incidence of syncope is variable, with as many 25–50% of young adults recalling at least one episode in their past. The incidence of those seeking medical attention is about 126 per 100,000.17Girls are seen for evaluation more frequently than boys.18Data from a group of male college and postgraduate students found an incidence of 15.5%, whereas a study among basic trainees in the U.S. Air Force demonstrated an inci-dence of 22.3%.16 The most common forms of syncope are more frequent during adolescence than in early child-hood. The single exception is the pallid breath-holding spell of the toddler. Numerous studies have estimated that at least 5% of children between 6 and 18 months of age have demonstrated some form of a breath-holding spell.15
Symptoms and Clinical Associations
The child may present with nausea, vomiting, pal-lor, diaphoresis, dizziness, weakness, or frank syncope.
There may be a sensation of an increased heart rate.
Premonitory symptoms can occur without a true syn-copal event and are referred to as near syncope or pre-syncope. Presyncope is a sense that one is “about to pass out.” Patients often complain of an impending loss of consciousness accompanied by nausea and visual phenomena of blurring, dimming, or partial loss, and also by auditory symptoms of diminished hearing and lightheadedness, but without true syncope. The approach to presyncope is essentially the same as that for syncope.19
The description of syncope can be variable with terms such as dizziness, lightheadedness, and presyncope often used for the same symptom complex. Vertigo, dise-quilibrium, and seizures are often confused with syn-cope. Dizziness is a symptom that needs better defi-nition to distinguish it from lightheadedness or vertigo.
The principal distinction is the description of the sensa-tion of mosensa-tion. Swaying, whirling, and spinning of the environment or room are characteristics of vertigo.
Alteration of balance or perception of the environment or a feeling of spinning often describes dizziness. Hyper-ventilation can result in lightheadedness. Sensations of dizziness or lightheadedness may be frequently associ-ated with psychological distress, including anxiety, depression, and panic attacks.19
Disequilibrium refers to balance problems without vertigo. This sensation is often unrelated to position or movement; the characteristic feature on history is diffi-culty ambulating. A fairly rare complaint among children, disequilibrium in the young is often caused by vestibular pathology or ataxia.19
Making the distinction between a seizure and syncope is important. Absence seizures and temporal lobe epilepsy can be described by younger patients and observers in a manner that appears to be syncope. Both phenomena result in an impairment of consciousness.
Seizures tend to occur and to resolve independent of position or posture; however, most pediatric syncope is related to position or volume status and is resolved quickly with supine posture without a postictal state.
True vasodepressor syncope ( VDS) does not occur in the supine position but may occur while sitting. Standing or rising to standing are the most common positional rela-tionships.
Etiology
Categories of syncope include noncardiac, cardiac, and neurocardiogenic (Box 1-4). Syncope in most young patients will not be life-threatening, but the physician’s aim must be to identify the patient at risk for a serious event. If a true syncopal event has occurred, an accurate description of the event is often sufficient to alert the physician to the likely cause.
Box 1-4 Differential Diagnosis of Syncope
Excessive vagal tone or hypervagotonia Orthostatic
Anemia
Hypovolemia or dehydration
Postural orthostatic tachycardia syndrome Dysautonomia
CARDIAC Arrhythmias
Tachycardias
Supraventricular tachycardia or Wolff-Parkinson-White syndrome
Dilated cardiomyopathy (with metabolic causes, myocarditis, or anomalous left coronery artery from the pulmonary artery)
NEUROLOGIC
Drugs, toxins, or electrolyte disorders
PSYCHOGENIC
Hyperventilation or hysteria Conversion reaction
Noncardiac Syncope
Noncardiac syncope includes neurologic, metabolic, drug or toxin exposure, and psychogenic etiologies.
Neurologic Etiology
Certain neurally mediated or autonomic etiologies of syn-cope, such as breath-holding spells and VSD, can termi-nate with tonic-clonic movements, which can cause confusion with a true epileptic seizure. They may be referred to as convulsive syncope or anoxic seizures.
Convulsive disorders are easily identified when they have an aura or prodrome, generalized tonic-clonic seizure activity, or a postictal phase with confusion and lethargy.20
A syncopal event occurring while the patient is in a recumbent position is likely to be due to a seizure.16,20 These etiologies can be more difficult to identify when the patient has absence seizures without an aura,loss of motor tone, or postictal confusion. Akinetic seizures or “drop attacks”are most common between 2 and 5 years of age.20 Temporal lobe epilepsy ( TLE ) is usually accompanied by an aura, often a smell or a sense of fear or foreboding, and is longer in duration than absence seizures. TLE is associated with simple or complex semi-purposeful motor activity, also known as “automatism.” Loss of con-sciousness may be more gradual.20
Complex partial seizures may involve behavioral changes and may be difficult to diagnose with decreased responsiveness and awareness of self and surroundings.
Basilar artery migraine results in occipital headache, vertigo, visual symptoms, ataxia, confusion, or syncope, or a combination thereof. In the classic scenario, the headache and premonitory aura is severe enough to result in a vagally mediated syncope. In atypical presen-tations, there is no premonitory headache, but vasocon-striction occurs in the vertebrobasilar arterial supply, leading to syncope without a change in heart rate or blood pressure. Diagnosis may be difficult to make with-out the input of a neurologist. Basilar artery migraine may account for up to 24% of childhood migraines, espe-cially in adolescent females.21
Metabolic Etiology
Hypoglycemia is an uncommon cause of syncope in chil-dren.20 Preceding symptoms of hypoglycemia can be divided between the neuroglycopenic and sympatho-mimeticsymptoms. The sympathomimetic symptoms consist of tachycardia, mydriasis, and diaphoresis. The neuroglycopenic symptoms consist of irritability, emo-tional lability, confusion, lethargy, and syncope. Causes of hypoglycemia in children include diabetes, ketotic hypoglycemia, liver enzyme deficiencies, and inborn errors of metabolisms such as medium chain acyl-coenzyme A dehydrogenase ( MCAD) deficiency.
Drug and Toxin Exposure
Illicit drugs such as 3,4-methylenedioxy-N-methylam-phetamine ( MDMA or Ecstasy), cocaine, or others, as well as a variety of prescribed drugs, can result in syn-cope from a variety of causes, most commonly from arrhythmias triggered by the drugs or by increasing the likelihood of orthostatic hypotension.
Psychogenic Etiology
Hyperventilation, most commonly associated with unrecognized anxiety or distress, occasionally results in syncope.20Although the exact mechanism is not clearly understood, hypocapnia, resulting in alkalosis and reduc-tion in regional cerebral blood flow from cerebral vaso-constriction, plays an integral role. Patients, who are usually adolescents, will rarely provide this aspect of the history and often present with the primary complaint of
“chest tightness” or “smothering.” A detailed history may uncover frequent panic attacks, which result in hyperventilation episodes and syncope. Hysterical syn-cope or conversion reaction mimics loss of conscious-ness and most commonly occurs in adolescents in the presence of an audience. Patients are typically calm when describing the episodes.20There are no abnormal-ities of heart rate, blood pressure, or skin color during the episodes, which may have an unusually long dura-tion. The patient typically falls without injury.20,22 Position may be supine in these situation. Frequently, an internalized stress can be uncovered by a psychiatrist or
psychologist, and syncope can be resolved with therapy for the underlying issue.
Cardiac Etiology
Syncope without warning is more likely to be cardiac in origin, as is exertional syncope.16,20A careful history often reveals that the syncope occurs during or shortly after exercise. Such a history should always be of serious concern to the astute clinician. The catecholamine surge associated with exercise makes a vagally mediated phe-nomenon unlikely as an explanation for syncope that occurs during the period of exertion.
The exception is the volume-sensitive athlete who has maintained suboptimal hydration throughout exer-cise and develops hypotension in the face of the periph-eral vasodilatation associated with exercise. Such patients should receive the thorough evaluation war-ranted for exercise-induced syncope before the episodes can be attributed confidently to neurally medi-ated phenomena.
Causes of exercise-induced or cardiac syncope can be separated into three broad categories. First is low output on a primary cardiac basis from obstruction, including obstructed inflow, as in cardiac tamponade or from car-diac tumors (external or internal), and obstructed out-flow, as seen in hypertrophic cardiomyopathy or aortic stenosis. Symptoms from obstructive tumors, such as myxomas, may be paroxysmal and are often associated with changes in position.20Obstruction can occur with pulmonary vascular disease and is seen with primary pul-monary hypertension or Eisenmenger’s syndrome.
Another cause of cardiac syncope occurs with myocardial dysfunction with poor cardiac contractility associated with primary myopathy. Cardiomyopathy, associated with neuromuscular disorders such as Duchenne’s muscular dystrophy, can result in syncope.
Cardiomyopathies may be associated with low output, but more commonly, these patients have syncope from associated arrhythmias.20Ventricular dysfunction can occur in the presence of inflammatory or ischemic heart disease. Myocarditis from a viral etiology would be the most common in this category. Kawasaki disease is asso-ciated early with inflammation of coronaries and myocardium, and later with ischemic coronary disease from coronary aneurysms with stenosis or thrombosis.
Other causes of ischemia from coronary anomalies include abnormal-course or intramural coronary artery, anomalous origin from the pulmonary artery, and athero-sclerotic coronary disease, particularly with postcardiac transplant arteriopathy or with homozygous familial hypercholesterolemia.
A third major category of cardiac syncope occurs in association with a variety of arrhythmias that interrupt the cardiac output (Fig. 1-3). Rhythm disturbances may decrease cerebral perfusion from a heart rate that is either
Figure 1-3 A, A 15-lead ECG in a patient with LQTS. The corrected QT (QTc) in this patient is 610 ms.(normal < 460 ms).B, Rhythm strip demonstrating a coarse wide complex tachycardia with a constantly “twisting axis” consistent with torsades de pointes.C, 15-lead ECG demonstrating a right bundle branch block pattern in an 18-year-old and S-T segment elevation in the right precordial leads ( V1–V3) consistent with the diagnosis of Brugada syndrome.
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Figure 1-3, cont’d D, 15-lead ECG demonstrating an occasional narrow complex sinus rhythm interrupted by a regular wide QRS tachycardia, consistent with ventricular tachycardia.E, 15-lead ECG demonstrating a short PR interval, a slurred upstroke of the QRS (delta wave), and absence of septal Q waves (in V6) diagnostic of the WPW anomaly.F, 15-lead ECG demonstrating a coarse, poorly organized wide QRS pattern consistent with ventricular fibrillation.
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too slow or too fast. These include ventricular arrhyth-mias, seen with arrhythmogenic RV dysplasia, idiopathic or catecholamine-induced ventricular fibrillation/ventric-ular tachycardia ( VF/ VT ), long QT syndrome with tor-sades de pointes, Brugada syndrome,VT with structurally normal hearts, and also seen in specific postoperative congenital heart defects, most commonly tetralogy of Fallot or similar lesions. Atrial tachyarrhythmias may result in syncope, as seen in the WPW syndrome, with atrial fibrillation and rapid ventricular response, which can lead to ventricular fibrillation. Atrial flutter with rapid AV conduction, seen after intraatrial repairs of D-TGA or
after the Fontan repair for single ventricle physiology, can result in syncope and sudden cardiac death. Syncope can be seen with supraventricular or ventricular tachycardia (SVT or VT ), more commonly in association with a struc-turally or functionally abnormal heart,although very rapid tachyarrhythmia can cause syncope in the presence of a normal heart. Less frequently, slow rhythms, including high-degree atrioventricular block and sick sinus syn-drome with periods of asystole, can also be responsible for syncope. Hypercyanotic “spells” may be seen in conjunc-tion with an existing right-to-left shunt, most commonly described in TOF. A spell frequently begins with an illness Figure 1-3, cont’d G, 15-lead ECG demonstrating an irregularly irregular narrow complex
tachycardia with an absence of true P waves. There are flutter waves with variable AV conduction.
This represents atrial flutter with variable AV block.H, ECG of narrow complex tachycardia. There is evidence of retrograde P waves. This is consistent with a diagnosis of supraventricular tachycardia.
or dehydration accompanied by a crying episode.
Increased resistance to pulmonary blood flow, combined with decreased resistance to systemic blood flow,can result in a spiraling cycle of cyanosis, hypoxemia, and syncope.
Autonomic Nervous System Neurally Mediated Syncope
Neurally mediated syncope, also referred to as auto-nomic, neurocardiogenic, vasovagal or vasodepressor syncope, common or emotional syncope, or reflex syn-cope, is the most common cause of syncope in the pedi-atric patient.20It includes syncope associated with the following: emotional stress and fear; pain; physical situa-tions such as overheating, physical exhaustion, dehydra-tion, and hypovolemia; anemia; prolonged standing or sitting; and a change in position from supine to standing or kneeling to standing.
Neurally mediated syncope is thought to be medi-ated by abnormal or heightened autonomic responses to various stimuli. Peripheral vasodilatation occurs with a decrease in blood pressure and a slow heart rate. The prodromal symptoms often consist of lightheadedness, nausea, pallor and diaphoresis, and visual or auditory loss. Usually the patient collapses suddenly and remains unconscious for less than 1 minute unless attempts are made to restore upright posture, which can result in exacerbation of symptoms or can prevent resolution of symptoms. The patient may remain pale, weak or tired, and diaphoretic following the episode.20 These episodes occur while the patient is standing, sitting, or on chang-ing from a sittchang-ing to a standchang-ing position but do not occur in the supine position. A number of reflex and compen-satory neurocardiovascular mechanisms allow individuals to change position, to adjust to physical exercise, to digest food, and to respond to unexpected or unpleasant mental stresses. These adaptive autonomic nervous system mechanisms preserve arterial blood pressure and cere-bral perfusion. Syncope can occur when afferent, cen-tral, or efferent portions of the autonomic reflex arc are impaired, myocardial contractility or vascular reactivity is suppressed, hypovolemia is present, hormonal responses are abnormal, or adaptive responses are inade-quate.
On standing, pooling of up to 25% of the cardiac out-put occurs in the lower extremities. A decrease in venous return and, thus, decrease in cardiac output and blood pressure occur. The baroreceptors or stretch receptors detect these changes and relay information to the central nervous system with a resultant decrease in parasympathetic tone, allowing for an increase in heart rate. There is a concomitant increase in sympathetic out-flow, which increases norepinephrine secretion and increases peripheral resistance. Blood pressure and cerebral perfusion are preserved.
Abnormalities can occur at one or several parts of this reflex arc. The traditional hypothesis regarding neurocar-diogenic syncope is that such episodes arise from vagally mediated hypotension (vasodepressor type), bradycardia (cardioinhibitory type), or both (mixed type), in part associated with vigorous contraction of a relatively empty ventricle.22 It is generally agreed that there is an increase in parasympathetic tone and inhibition of sympathetic outflow. The initial mechanism relates to a decrease in systemic venous return and excessive vagal stimulation associated with the decrease in ventricular filling. Normal autonomic reflexes do not function nor-mally in these patients. The initial stimulus is venous pooling of blood within the vascular system, the vasodila-tor effects of adrenaline, decreased production of norepi-nephrine by the adrenal, an under-representation of α receptors or over-representation or hypersensitivity ofβ receptors, or else stimulus by a primary neurogenic process.20,22 In the presence of hypotension, sympa-thetic activation results in an increase in catecholamine release with more forceful cardiac contractions and sub-sequent mechanoreceptor stimulation. Although heart rate typically does increase prior to the syncopal episode, cardiac output does not increase sufficiently in response to the decrease in blood pressure.15,20Sympathetic with-drawal and increased parasympathetic activity ensue with hypotension, bradycardia, and syncope. A poorly understood central nervous system reflex, in response to pain, fear, the sight of blood, or anxiety, triggers sympa-thetic inhibition with vasodilatation and parasympa-thetic activation with bradycardia, resulting in syncope.
Reflex or Situational Syncope
An amplified or inappropriate reflex response to a physi-ologic stressor can result in syncope. Pallid breath-hold-ing spells are a common pediatric reflex phenomenon, usually beginning in infancy or early childhood. An unex-pected, startling stimulus elicits a sudden reflex increase in vagal tone and resultant asystole for up to 15 seconds.
As the episode nears conclusion, there may be accompa-nying tonic-clonic seizure activity. The more common type of breath-holding spell follows a period of crying, terminated with sustained exhalation (often against a closed glottis) and visible cyanosis. This is followed by vagally mediated hypotension and syncope. Reflex syn-cope may be associated with swallowing, stretching, hair combing, sneezing, and diving. Cough, defecation, and micturition syncope are related to increased intratho-racic pressure, leading to vagally mediated reduction in cardiac output.20
Carotid Sinus Syncope
Carotid sinus baroreceptors are located above the com-mon carotid artery, in the internal carotid artery. Shaving or turning the head with a tight collar, anomalies of the
cervical vertebrae, or having pressure applied over the carotid sinus can initiate this reflex.
Hypervagotonia
Hypervagotonia, or excessive vagal tone, is primarily seen in 2- to 6-year-olds and is a result of an exaggerated vagal response that is not interrupted by normal reflexes.
Generally, there is a vagal stimulus, but not the type that elicits breath holding. Most children with this condition gradually have resolution, but they may require treatment with medication such as atropine for a period of time.
They commonly develop vasodepressor syncope as ado-lescents. Both conditions are most likely manifestations of autonomic nervous system abnormalities or imbal-ance. Many individuals, especially in late childhood and early adolescence, have increased vagal tone that mani-fests as a low resting heart rate, junctional rhythm, or varying degrees of AV block, especially during sleep. This
They commonly develop vasodepressor syncope as ado-lescents. Both conditions are most likely manifestations of autonomic nervous system abnormalities or imbal-ance. Many individuals, especially in late childhood and early adolescence, have increased vagal tone that mani-fests as a low resting heart rate, junctional rhythm, or varying degrees of AV block, especially during sleep. This