Sharon E. Mace
Syncope is the sudden transient loss of consciousness (LOC) accompanied by an inability to maintain postural tone, with spontaneous resolution. The sensation or feeling of being about to pass out is near-syncope or presyncope. The causes and management are analogous to that for syncope. Syncope is a common complaint in patients of all ages, accounting for 1% to 1.5% of emergency department (ED) visits and up to 6% of hospital admissions (1,2). In children and adolescents, syncope accounts for 2% of pediatric ED visits (3) and 5% of pediatric hospital admissions (4,5). In the pediatric population, syncope occurs more often in females than males, and most often in adolescents, with the highest incidence in the 15- to 19-year-old age group (6). About 25% of all adolescents will have had at least one syncopal episode (7), although higher incidences of nearly 50% have been reported (8,9).
The etiology of syncope is established in only about half of adult patients following an initial ED visit and in only 70% of patients who have been admitted to the hospital (10). The findings in pediatric patients are similar where nearly one in five patients have “syncope of unknown origin” (11).
Syncope of unknown origin is less common in children under 5 years of age, in whom primary cardiac dysrhythmias, seizures, and breath-holding spells are the main considerations. Although the general categories of disorders resulting in syncope are similar in adults and children, the specific causes and evaluations differ between adults and children/infants.
The pathophysiology of syncope involves dysfunction of cerebral hemispheres or the reticular activating system in the brainstem, typically from an acute decrease in cerebral blood flow. Syncope occurs when cerebral blood flow decreases to less than 30% to 50% of baseline (12). This is most often the result of systemic hypotension, but may also be due to cerebral vasoconstriction or regional hypoperfusion of the central nervous system (CNS). Decreased cerebral perfusion impairs delivery of substrate (e.g., oxygen and glucose) to the brain. Less commonly, cerebral blood flow is adequate, but there is deficient substrate, as in hypoglycemia, carbon monoxide poisoning, severe anemia, or asphyxia.
CLINICAL PRESENTATION
Vasovagal syncope, also known as neurocardiogenic, neurally mediated, vasodepressor, and reflex syncope, is the most common cause of pediatric and adult syncope. It is responsible for about half of cases of pediatric syncope (11,13). Typical cases are individuals who faint while experiencing pain, anger, or fear (e.g., at the sight of blood), or while standing erect for a prolonged time in a warm environment (as in the military, a parade, or a religious service).
The mechanism of vasovagal syncope has been thought to be a vagally mediated reflex that causes bradycardia, and a decreased peripheral vascular resistance with venous pooling in the periphery resulting in hypotension from a loss of sympathetic tone. Decreased venous return leads to a relatively empty ventricle. Strong myocardial contractions against an empty ventricle stimulate the vagal reflex causing bradycardia, and sympathetic withdrawal results in decreased peripheral vascular resistance and a drop in arterial blood pressure. However, the occurrence of “vasovagal” syncope in patients with a heart transplant indicates that other mechanisms may also be responsible. Possibilities include neurohumorally mediated sympathetic inhibition, impaired responses in the peripheral vessels (affecting peripheral vascular resistance), and abnormal CNS control mechanisms, or a combination of such factors.
Cardiovascular causes of syncope can be categorized into several groups: dysrhythmia, obstruction to flow, myocardial dysfunction, or vascular. The common pathophysiology is a decrease in cardiac output (CO) resulting in decreased cerebral perfusion. Cardiac syncope occurs when CO is decreased from inadequate stroke volume (SV) or an abnormal heart rate (HR), leading to inadequate filling of the ventricles.
Although dysrhythmias are a less frequent cause of syncope in pediatric patients than adults, this possibility should be in the differential because of the association with sudden death. Patients with heart disease, whether congenital or acquired, are at high risk for dysrhythmias and sudden cardiac death. Congenital heart disease is the number one cause of dysrhythmias resulting in syncope in pediatric patients. Most sudden cardiac deaths associated with dysrhythmias occur in pediatric patients who are status after corrective cardiac surgery, especially repair of tetralogy of Fallot, or a baffle (Mustard or Senning procedure) for transposition of the great vessels. Estimates of the incidence of sudden cardiac death with congenital heart disease are as follows:
Tetralogy of Fallot 2.5% to 10%
Eisenmenger syndrome = 10% to 47%
Ebstein anomaly = 2.5% to 20% (14).
Other cardiac disorders associated with dysrhythmias include Ebstein anomaly, arrhythmogenic right ventricular dysplasia, and cardiac tumors.
In patients with a structurally “normal” heart, syncope and sudden death can occur with Wolff–Parkinson–White syndrome (WPW), long QT syndrome, short QT syndrome, ventricular tachycardia, complete heart block, and the Brugada syndrome.
The diagnostic hallmark of WPW is a short PR interval and a delta wave. Supraventricular tachycardia results from reentrant conduction down the atrioventricular node and up the accessory pathway (Kent bundle). Rapid conduction over the Kent bundle can proceed to ventricular fibrillation and sudden death. An electrophysiologic study with radio-frequency ablation is the recommended treatment.
The long QT syndrome is due to abnormal ventricular depolarization resulting in a prolongation of the refractory period. This can cause torsades de pointes with the potential to degenerate into ventricular fibrillation and sudden death. The long QT syndrome is characterized by QT interval prolongation. There are several forms of the long QT syndrome. The congenital types of long QT syndrome include the Romano–Ward syndrome and the Jervell and Lange-Nielsen syndrome. The Romano–Ward syndrome has an autosomal dominant inheritance, whereas the Jervell and Lange–Nielsen syndrome has an autosomal recessive inheritance and deafness. Acquired prolongation of the QT interval can be due to electrolyte abnormalities (hypocalcemia, hypokalemia), drugs/overdose, and increased intracranial pressure. Medications associated with prolongation of the QT interval include psychotropics (tricyclic antidepressants, phenothiazines), antihistamines, and promotility drugs (such as cisapride), especially in combinations with other medications (e.g., erythromycin and ketoconazole). The short QT interval is also associated with dysrhythmias and sudden death.
Bradyarrhythmias, which can cause syncope and sudden death, include complete heart block and sick sinus syndrome. Atrioventricular block may be congenital or acquired. Acquired causes are most common after cardiac surgery; but rheumatologic diseases, infections, and neuromuscular diseases (e.g., Lyme disease, acute rheumatic fever, endocarditis, diphtheria, myotonic dystrophy, certain forms of muscular dystrophy, and Kearns–Sayre disease) are other etiologies for complete heart block. Congenital heart block can occur as an isolated condition or with structural heart disease, especially defects of the atrioventricular septum, L-transposition of the great vessels, or ventricular inversion. Infants born to mothers with systemic lupus erythematosus may have complete heart block secondary to transplacental antibodies cross-reacting with fetal cardiac tissue.
Sinus node dysfunction most commonly occurs in patients who have undergone cardiac surgery, especially atrial surgery. These patients are also at risk for atrial arrhythmias (e.g., atrial flutter and atrial fibrillation). The combination of atrial flutter/fibrillation with a rapid ventricular response plus sinus node dysfunction can lead to syncope from hemodynamic compromise and is a harbinger for dysrhythmias and sudden death.
Ventricular tachycardia/fibrillation leading to syncope and sudden death can occur in patients with myocardial disease (such as myocarditis, cardiomyopathy, and myocardial ischemia) and with ventricular damage or scarring post cardiac surgery (even years after surgical repair).
The second category of cardiac syncope involves obstruction to blood flow. The classic example is hypertrophic obstructive cardiomyopathy. Aortic stenosis with outflow obstruction may cause syncope, anginal chest pain, and dyspnea on exertion. Severe coarctation of the aorta or severe mitral valvular disease can also present with syncope. Similarly, patients with primary pulmonary hypertension or severe pulmonic stenosis may develop syncope. Sudden death in Eisenmenger syndrome is probably due to a drop in blood flow from a sudden increase in pulmonary vascular resistance. Tumors such as an atrial myxoma causing decreased CO are a rare cause of cardiac syncope.
Myocardial disease is the third category of cardiac syncope and includes cardiomyopathies, myocarditis, myocardial ischemia (congenital from anomalous coronary arteries or acquired as in Kawasaki disease), and diseases infiltrating/destroying the myocardium such as amyloidosis or Chagas disease.
Vascular causes of syncope include aortic dissection, subclavian steal, thoracic outlet syndrome, and very rarely pericarditis leading to tamponade.
Respiratory diseases ranging from status asthmaticus to severe pneumonia or any cause of respiratory failure resulting in hypoxemia can cause syncope from decreased oxygen delivery to the brain. Posttussive or cough syncope, occurring after severe coughing, is due to decreased venous return (and, thus, decreased CO) caused by the Valsalva maneuver. Cough syncope is a type of vasodepressor syncope. Pulmonary emboli (PE) while in the respiratory system exert their effect by obstruction of blood flow.
Other respiratory causes of syncope include breath-holding spells, which are unique to pediatrics, and hyperventilation. Hyperventilation syncope generally occurs when there is an emotional upset, pain, or anxiety, and is often associated with light-headedness, tachypnea, dyspnea, chest pain, and paresthesias. The pathophysiology is thought to be from decreased oxygen/glucose delivery to the brain caused by vasoconstriction of the cerebral arteries from the hypocapnia caused by hyperventilation.
Breath-holding spells are common, occurring in about 4.6% of children (15). Breath-holding spells usually begin between 6 to 18 months of age (with a range from the first week of life to 3 years) and end by 6 years of age in 90% of children. There are two types of breath-holding spells: cyanotic and pallid. Cyanotic spells are more common. Both spells are due to transient cerebral anoxia.
Typically, the cyanotic breath-holding spell is precipitated by the child’s or infant’s crying after being angered. The vigorous crying results in transient cerebral ischemia caused by (a) cerebral arterial vasoconstriction from hypocapnia, (b) hypoxemia from apnea, and (c) decreased CO from a prolonged Valsalva effect. The pallid breath-holding spell generally occurs after a painful or anxiety-producing incidence such as a minor fall. The transient cerebral ischemia occurring with the pallid breath-holding spell is due to an exaggerated vagal response to pain causing prolonged asystole or bradycardia. Breath-holding spells are a benign entity with no sequelae although they are commonly misdiagnosed as seizures.
Neurologic syncope can occur as a result of cerebral hypoperfusion from cerebral vasoconstriction (as with hyperventilation syncope) or from focal hypoperfusion of CNS structures. Cerebrovascular disease (more common in adults) could cause syncope, but usually there are other neurologic signs and symptoms. Other causes of syncope from focal hypoperfusion of CNS structures include subarachnoid hemorrhage, vasculitis (affecting cerebral vessels), CNS tumors, CNS trauma, and basilar artery migraine.
Psychiatric “disorders” are in the differential diagnosis of syncope. “Hysterical syncope” usually occurs before an audience, with no injuries occurring to the patient, and often is accompanied by dramatic moaning, gestures, and attention-seeking behavior with secondary gain.
The most common final diagnoses, according to a pediatric ED study of syncope in children and adolescents, were vasovagal (50%), orthostatic hypotension (20%) due to dehydration (15%) or anemia (5%), atypical seizure (7.5%), migraine (5%), and minor head trauma (5%) (13). A multicenter inpatient study of pediatric syncope from China reported the following causes of syncope; autonomic mediated reflex syncope (73%) consisting of vasovagal 43%, postural orthostatic tachycardia syndrome (POTS) 27%, situational 1.7%, and orthostatic hypotension 1.3%; followed by cardiac syncope 2.9%, neurologic syncope 2.1% consisting of seizure 1.9% and migraine 0.2%; psychiatric syncope 2.3%, metabolic syncope 0.8% comprised of hypoglycemia 0.4%, severe anemia 0.2% and hyperventilation syndrome 0.2%, and unknown origin 18.9% (11). Although it is likely that the ED and inpatient populations are different in these two studies, the most common cause of pediatric syncope in all age groups, whether ED or inpatient, is vasovagal with cardiac and neurologic syncope generally both <5%.
DIFFERENTIAL DIAGNOSIS
Not all patients with a “transient loss of consciousness” are diagnosed with syncope (Table 235.1). In one study of adults presenting to an ED with an LOC, 12.3% of patients had a diagnosis other than syncope (1). The nonsyncope patients were categorized as either a disorder with LOC or a disorder mimicking an LOC. For the group with a disorder with LOC, hypoglycemia accounted for the majority of patients, with other diagnoses including transient ischemic attack, seizure, migraine, and other metabolic (hypoxia, hyperventilation) causes. Somatization disorders and drop attacks comprised the category of disorders mimicking an LOC (1). Another ED study diagnosed seizures in 29% of patients who presented with a transient LOC (16). Comparable results were noted in a study of pediatric syncope patients with a neurologic condition diagnosed in 17.5% (atypical seizure 7.5%, migraine 5%, minor head trauma 5%) 13).
TABLE 235.1
Causes of Syncope in the Pediatric Patient
Thus, the main considerations for other “nonsyncopal” causes of a transient LOC are either a neurologic disease or a metabolic disorder. Neurologic disorders range from an acute neurologic event from a transient ischemic attack/cerebrovascular accident or hemorrhage/emboli to a migraine or seizures. Neuropathies can precipitate orthostatic (postural) hypotension and syncope. The differential illustrates the importance of the neurologic examination in any patient with syncope.
Hypoglycemia is the most common diagnosis in the metabolic/endocrine category of patients who may present with a transient LOC. Hyperventilation, drugs (alcohol/illicit drugs/prescription drugs), toxins, liver failure, renal failure, various congenital metabolic disorders, and carbon monoxide poisoning are also in the differential.
Seizures are often mistaken for syncopal events and vice versa. Brief tonic–clonic movements may occur with vasodepressor syncope. Akinetic seizures may be present like a syncopal episode. The history may help distinguish between syncope and a seizure. The following suggest a seizure, not syncope: focal neurologic signs, bowel/bladder incontinence, prolonged LOC or confusion, tongue biting, and a prodromal aura. With a syncopal episode, the period of unconsciousness is brief (only seconds) and has a rapid recovery to a normal mental status.
ED EVALUATION AND MANAGEMENT
The history and physical examination are the key components of the evaluation of the pediatric patient with syncope. After ruling out mimickers of pediatric syncope, such as seizures and breath-holding spells, the first consideration is to determine whether the etiology of the syncope is benign or life-threatening. With near syncope or presyncope, the syncopal symptoms resolve before LOC occurs. The evaluation of the near syncope patient, however, is similar to that of the syncope patient.
The history and physical examination should guide the ordering of laboratory and ancillary tests. If the history is pathognomonic, such as vasodepressor syncope (e.g., teenager who passed out while getting a routine immunization) or an infant with a breath-holding spell, further testing may not be necessary. If the history suggests orthostatic syncope due to dehydration from vomiting or diarrhea, checking electrolytes and providing intravenous fluids may be all that is needed.
The physical examination may provide clues to the diagnosis. Cardiac findings, such as a murmur, loud S2, the presence of a click, S3, or S4, suggest cardiac syncope. The presence of neurologic symptoms and signs may indicate CNS disease or a seizure. If there are differences in pulses and/or blood pressures between the extremities, consider the possibility of a dissecting aneurysm, a coarctation of the aorta, or subclavian steal. Focused testing in selected patients based on the history and physical examination is probably the most useful and cost-effective approach (17,18). Simple cost-effective tests may be helpful, such as abnormal orthostatic vital signs, supine tachycardia, or severe dizziness upon standing (3,13), suggesting orthostatic syncope; or hemoccult of the stool with melena, indicating gastrointestinal bleeding. A pregnancy test should be considered in female adolescents with syncope, as bleeding during pregnancy (as with ectopic pregnancy) can cause syncope. Patients with hypoglycemic symptoms can present with syncope, and thus a serum glucose or dextrostix might be useful, especially in a diabetic. When pallor is present or bleeding is suspected, a hematocrit is appropriate.
If cardiac syncope is being considered, an electrocardiogram (ECG) and chest roentgenogram are indicated. Additional evaluation such as an echocardiogram, Holter monitoring, pediatric cardiology consultation, or hospital admission may be warranted if cardiovascular syncope is strongly suspected and supported by the evaluation (3).
Many clinicians recommend an ECG in any pediatric or adult patients with syncope no matter the history to detect occult cases of cardiovascular syncope (4,7,17,18).
Routine computed tomography (CT) scans are usually not helpful, but a head CT scan may be indicated if neurologic signs/symptoms are present or new onset of seizures is a likely diagnosis. A chest CT scan or ventilation perfusion scan can be done if PE is a consideration. However, in the adolescent population a D-dimer may be useful to rule out PE and avoid unnecessary CT scanning. If orthostatic syncope from a dysautonomic syndrome is being considered, referral for tilt testing may be appropriate. The tilt test has been useful in selected pediatric patients, including those with “unexplained” syncope (19).
Several rules have been developed including the San Francisco Syncope Rule and the OESIL (Osservatorio Epidemiologico sulla Sincope nel Lazio) in order to predict which patients with syncope are likely to have an adverse outcome (2,20). However, these rules apply only to adults and prospective studies indicate clinical judgment performs as well as these rules (21,22).
CRITICAL INTERVENTIONS
• Obtain a clear history of the events prior to, during, and immediately after the syncopal event.
• Perform a thorough physical examination (particularly cardiac and neurologic), in addition to orthostatic vital signs.
• Perform a blood glucose in patients with altered level of consciousness and a urine pregnancy test in adolescent females.
• Obtain an ECG on patients with syncope, especially those with possible cardiac syncope to check for long QT syndrome, WPW syndrome, and other causes of cardiac syncope. A chest radiograph may be indicated in selected patients with ECG findings indicative of cardiomyopathy.
• Consider all patients with a history of cardiac disease (congenital or acquired, especially those who have had heart surgery) to have a potentially life-threatening dysrhythmia as the cause of their syncope.
DISPOSITION
Testing, referral, and the decision to admit to the hospital are generally guided by the findings on the history, physical examination, and ECG. Although most causes of syncope are benign, some are life-threatening, and syncope may be a warning sign of later sudden death. Thus, patients with cardiac syncope typically require referral and admission. Patients experiencing vasopressor syncope or breath-holding spells may be discharged home without additional testing. Patients with orthostatic syncope from dehydration can usually be treated with intravenous fluids in the ED and then discharged home. Patients with a dysautonomic syndrome generally need to be referred.
Common Pitfalls
• Failure to differentiate syncope from seizures and breath-holding spells.
• Failure to recognize potentially life-threatening causes of syncope.
• Failure to identify the high-risk patient (e.g., the patient with congenital heart disease or a history of cardiac surgery) and refer or admit to the hospital.
• Failure to perform a pregnancy test on sexually active adolescent females.
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