Derya Caglar
EPIDEMIOLOGY
Syncope is common in adolescents and less common in younger children. Between 20% and 50% of adolescents experience at least one episode of syncope. This condition is transient and usually self-limited.
The most common type of benign syncope is neurally mediated (vasovagal) syncope.
Twenty percent of children referred to a cardiologist or neurologist for evaluation are diagnosed with a serious illness.
The rate of sudden unexpected death in children is 2.3% of all pediatric deaths. Sudden cardiac death makes up about one-third of these cases.
Except for trauma, sudden cardiac death is the most common cause of sports-related deaths, more commonly associated with basketball, football, and track.
The two most common causes of sudden cardiac death in adolescent athletes without known cardiac disease are hypertrophic cardiomyopathy and aberrant coronary arteries.
Other causes of sudden cardiac death in children are myocarditis, cardiomyopathy, congenital heart disease, and conduction disturbances.
PATHOPHYSIOLOGY
Syncope is the temporary loss of consciousness from reversible disruption of cerebral functioning, and is usually caused by inadequate cardiac output causing cerebral hypoperfusion.
Vascular syncope occurs when venous pooling occurs in the legs, leading to a decrease in ventricular preload with a compensatory increase in heart rate and myocardial contractility.
Neurally mediated syncope (NMS), or reflex syncope, occurs when receptors in the atria, ventricles, and pulmonary arteries sense a decrease in venous return, and an efferent brain stem response via the vagal nerve causes bradycardia, hypotension, or both. Types of NMS include vasovagal, orthostatic, situ-ational (urination, coughing), and familial. NMS is usually preceded by sensations of nausea, warmth, or lightheadedness, with a gradual visual grayout.
Cardiac syncope occurs when there is an interruption of cardiac output from an intrinsic cardiac problem. These causes are divided into tachydysrhythmias, bradydysrhythmias, outflow obstruction, and myocardial dysfunction. Syncope resulting from these causes usually begins and ends abruptly and may be exercise induced.
Long QT syndrome may be inherited or acquired, is associated with hypertrophic cardiomyopathy, and accounts for half of the cases of sudden cardiac death. Patients with long QT syndrome have a QTc >0.44 seconds on ECG. Drugs that prolong the QT interval include antibiotics, tricyclic antidepressants (TCAs), antipsychotics, antifungals, GI motility and antinausea agents, antihista-mines, antiarrhythmics, and appetite suppressants.
Other known causes of syncope include breath holding, hyperventilation, hypoglycemia, hysteria, and atypical migraines.
Any event that causes sufficient cerebral hypoperfusion can lead to sudden death.
CLINICAL FEATURES
Syncope is the sudden onset of falling, accompanied by a brief episode of loss of consciousness.
Involuntary motor movements may occur with all types of syncopal episodes, but are most common with seizures.
Two-thirds of children experience lightheadedness or dizziness prior to the episode.
Table 80-1 lists the most common causes of syncope by category.
Structural cardiac disease, cardiac dysfunction, rhythm disturbances, and systemic disease are predisposing factors for sudden cardiac death.
Risk factors associated with serious causes of syncope include exertion preceding the event, a personal or family history of cardiac disease or dysfunction, recurrent episodes, associated chest pain or palpitations, or prolonged loss of consciousness (see Table 80-2).
Events easily mistaken for syncope are presented in Table 80-3 along with common associated symptoms.
TABLE 80-1 Causes of Syncope in Children and Adolescents
TABLE 80-2 Risk Factors for Serious Causes of Syncope
Exertion preceding the event
History of cardiac disease in patient
Recurrent episodes
Recumbent episode
Family history of sudden death, cardiac disease, deafness
Chest pain, palpitations
Prolonged loss of consciousness
Medications that affect cardiac conduction
TABLE 80-3 Events Mistaken for Syncope
Basilar migraine: headache, loss of consciousness, neurologic symptoms
Seizure: loss of consciousness, simultaneous motor movements, prolonged recovery
Vertigo: no loss of consciousness, spinning or rotating sensation
Hysteria: no loss of consciousness, indifference to the event
Hypoglycemia: confusion, gradual onset associated with diaphoresis
Breath-holding spell: crying prior to the event, age 6–18 months
Hyperventilation: severe hypocapnia can cause syncope
DIAGNOSIS AND DIFFERENTIAL
No specific historical or clinical features reliably distinguish between vasovagal syncope and other causes. However, a thorough history and physical examination, with particular focus on the cardiac examination, can help to arouse suspicion for serious causes.
The most important step in evaluation of children with syncope is a detailed history, including medications, drugs, intake, and food.
Syncope during exercise suggests a more serious cause. Many of the diseases that cause syncope also cause sudden death in children. Approximately 25% of children who suffer sudden death have a history of syncope. However, syncope is a very common event, and a syncopal episode by itself is not associated with an increased risk of sudden death.
If witnesses note that the patient appeared dead or cardiopulmonary resuscitation was performed, a search for a serious pathologic condition must be undertaken.
Cardiac dysrhythmia should be suspected if syncope is associated with fright, anger, surprise, or physical exertion.
The physical examination should include a complete cardiovascular, neurologic, and pulmonary examination. Any abnormalities noted in the cardiovascular examination require additional work-up.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Routine laboratory studies are not needed if vasovagal syncope is clearly identified from the history. Laboratory assessment is guided by the history, physical examination, and clinical suspicion. In patients with atypical presentation or worrisome symptoms, one might consider serum chemistry, hematocrit, thyroid function tests, a chest radiograph, and a urine drug screen.
An ECG should be done on all patients except those with a clear vasovagal episode. The QT interval should be assessed. Patients with hypertrophic cardiomyopathy, prolonged QT interval, or other cardiac dysrhythmias should be managed in consultation with a cardiologist.
An echocardiogram is recommended for patients with known or suspected cardiac disease.
Patients resuscitated from sudden death must have a complete evaluation including a creatinine phosphokinase level (CPK-MB) and troponin I unless a clear cause of the arrest is apparent. One should be alert for complications resulting from the arrest. All such patients should be admitted to a pediatric intensive care unit.
If no clear cause is found for the syncopal episode, the child may be discharged to be further evaluated and followed by the primary care physician, unless there are cardiac risk factors or exercise-induced symptoms, in which case referral to a cardiologist is warranted, and further participation in sports should be prohibited until cleared by cardiology.
Children with documented dysrhythmias should be admitted with continuous cardiac monitoring. Patients with a normal ECG but a history suggesting a dysrhythmic event are candidates for outpatient monitoring and cardiac work-up.
For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 140, “Syncope and Sudden Death in Children,” by William E. Hauda II and Maybelle Kou.