Syncope

After completing this article, readers should be able to:Syncope is a transient loss of consciousness and muscle tone. Loss of cerebral oxygenation and perfusion is the usual mechanism. It often is benign but may cause injury (15%of cases). Syncope can be caused by serious cardiac disease, which should be suspected whenever syncope occurs with exercise.Up to 3% of emergency department visits by adults and 6% of hospital admissions are due to syncope. Among children, only 0.125% of emergency department visits are due to syncope. Nevertheless, 47% of college students report having fainted, and 15% of children suffer from syncope before the end of adolescence. The lay public realizes that healthy children who faint frequently are free of serious disease and may not require emergency medical attention. About 75% of children who faint have neurocardiac (vasovagal) syncope due to neurally mediated hypotension and bradycardia; most others have seizures, migraine, or cardiac disease.The causes of syncope can be categorized as cardiac, noncardiac, and neurocardiac (TableT1). Cardiac syncope is due to outflow obstruction (aortic stenosis,hypertrophic cardiomyopathy), myocardial dysfunction (cardiomyopathy,carditis, ischemia), or arrhythmias(ventricular tachycardia, long Q-T syndromes, Wolff-Parkinson-White syndrome). Cardiac disease is suggested when syncope accompanies exercise. Cardiac syncope is potentially fatal and always deserves careful evaluation and treatment.This form of syncope includes many entities, some of which are distinguished easily by a careful history and are not true syncope. Seizures often manifest unusual eye or limb movements, may be prolonged,and—unlike syncope—usually are followed by postictal stupor. Seizures may result from cardiac or neurocardiac syncope if cerebral perfusion or oxygenation is sufficiently reduced, which is especially likely if the child is held upright during the syncopal episode. Epileptic seizures may cause cardiac disturbances, usually tachycardia. Many patients who have epilepsy have normal results on electroencephalography (EEG); diagnosis is made best by history.Breathholding spells begin in infancy and resolve by school age. The history is stereotypical. The spells always begin with pain or anger, followed in order by a brief cry, holding of the breath (usually with the mouth open and a distressed expression), cyanosis or pallor (the latter if bradycardia occurs),possibly a loss of consciousness, and finally perhaps a brief tonic or clonic seizure. If the history is not perfectly typical, epilepsy or cardiac syncope should be suspected and these diagnoses pursued. If the history is typical, iron deficiency anemia, which is a possible cause,should be ruled out, and the parents should be reassured that breathholding is benign and will resolve. Antiepileptic medications should not be prescribed to breathholders unless the resulting seizure is lengthy. Seizures related to breathholding usually are brief and hypoxic and do not require treatment with antiepileptic medication. Breathholding is not a manipulative behavior. Its only sequel is a later propensity to neurocardiac syncope in 17% of patients.The best treatment is to keep the child horizontal and wait.Migraine may cause syncope because of the pain or occasionally directly (brainstem migraine). The diagnosis can be made based on a history of associated severe headache with nausea, vomiting,photophobia, and relief by sleep. Family history is positive for migraine in 75% of cases.Orthostatic hypotension is defined as a 20-mm Hg drop in systolic blood pressure upon assuming an upright posture. Patients should be monitored for at least 2 minutes upright with serial blood pressure measurements. Pregnancy should be considered as a cause in women of childbearing age. Dehydration,prolonged bedrest, drugs, and neuropathies may be predisposing factors.Hyperventilation may produce sufficient cerebral vasoconstriction to cause syncope. An associated valsalva maneuver or chest compression can accentuate the cerebral hypoperfusion caused by hyperventilation.Situational syncope can be caused by cough, micturition, defecation,neck stretching, hair grooming,venipuncture, or even swallowing in certain individuals. The diagnosis is based on the history.Narcolepsy may mimic syncope. Those who have narcolepsy go to sleep abruptly. Cataplexy (the abrupt intrusion of rapid eye movement sleep into waking) may be mistaken for syncope if a history of excessive daytime sleepiness is not sought. Cataplexy may produce loss of consciousness in response to emotional reactions such as laughter or anger. Narcolepsy is diagnosed by the sleep latency test. Narcolepsy is common in children, a fact that was not appreciated until recently.Metabolic causes of syncope are rare, but hypoglycemia and electrolyte abnormalities should be considered because they could have serious consequences.Hysterical syncope may be difficult to diagnose, but it should be suspected when the episode is prolonged, there is no change in vital signs or appearance, it does not raise concern in the patient, or the patient’s recall or responsiveness during the event suggests that consciousness has been maintained.This is the most common variety of syncope, and it can be diagnosed with a tilt table test, although this test is not perfectly sensitive or specific. Approximately 25% of cases are precipitated by acute illness and anemia or by such noxious stimuli as pain, fear, exhaustion, hunger,prolonged standing, or crowded/poorly ventilated rooms.There usually are the following prodromal symptoms:nausea/vomiting, pallor, lightheadedness/vertigo,visual disturbances, sweating, and shortness of breath. After syncope,the patient may be fatigued,light-headed, anxious, or nauseous or may complain of headache. The typical mental alertness following the episode is helpful in distinguishing syncope from seizures.The pathophysiology of neurocardiac syncope is relatively well understood. Peripheral venous pooling leads to decreased ventricular filling and increased circulating catecholamines. The ventricle responds with vigorous contractions that stimulate mechanoreceptors (like hypertension) and produces a paradoxic withdrawal of sympathetic activity that causes hypotension,bradycardia, or both.The history is the key to diagnosis of syncope, and it must be obtained carefully both from the patient and from an eyewitness because the patient will be unreliable for observations during unconsciousness. Several points demand specific questioning: The past history may reveal associated disease predisposing to syncope. Because many causes of syncope are familial, it is important to inquire carefully about a family history of syncope, sudden or early death, epilepsy and neurologic disease, heart disease, and deafness(Q-T syndromes may have familial deafness).A general physical and neurologic examination must include measurement of vital signs and a cardiac evaluation. Approximately 90% of orthostatic hypotension occurs within 2 minutes of standing upright; such a finding provides an important clue to the diagnosis. Electrocardiography is recommended for every case of unexplained syncope. Life-threatening cardiac disease is a first concern. Other laboratory tests should be ordered according to findings from the history and physical examination. An EEG, video-EEG monitoring (if episodes are frequent),neuroimaging, or neurologic referral may help with suspected seizures. A multiple sleep latency test is used to diagnose narcolepsy. Determination of blood glucose or electrolyte concentrations or endocrinologic studies may be useful in selected cases. If cardiac disease is suspected, Holter or loop monitoring, chest radiography, echocardiography, exercise stress testing, or even invasive electrophysiologic testing may be pursued. The tilt table test has made the diagnosis of neurocardiac syncope a positive one rather than simply one of exclusion. Protocols vary, but the patient is tilted upright for a time sufficient to reproduce symptoms and changes in cardiovascular function (hypotension or bradycardia). The tilt table test is not always specific or sensitive, and intravenous infusions of isoproterenol and other drugs may be confusing noxious stimuli. Nevertheless, this has become the gold standard for diagnosing neurocardiac syncope. Treatment of syncope is directed at the specific causative entity. Cardiac disease may require antiarrhythmics or surgery. Seizures may require anticonvulsants, with the choice depending on the exact type of seizure. Breathholding spells, which can be upsetting, necessitate reassurance of parents. A variety of acute and prophylactic medications are available for migraine. Hysteria in childhood merits psychiatric evaluation and the consideration of abuse. The sleepiness of narcolepsy is treated with stimulants (eg,methylphenidate hydrochloride 20 mg every morning) and brief naps;cataplexy is treated with tricyclic antidepressants (eg, imipramine 25 to 75 mg q hs). For situational syncope, the inciting stimulus should be avoided.Neurocardiac syncope often can be managed with simple suggestions, such as lying down before losing consciousness, wearing elastic hose to prevent venous pooling in the legs, increasing salt and water intake, eating regularly, avoiding noxious stimuli that precipitate syncope, and intermittently contracting leg muscles when standing to increase venous return. Avoiding alcohol, beta-blockers, tricyclics, and isoproterenol may lessen the likelihood of neurocardiac syncope. Standard drug therapy includes mineralocorticoids (hydroflurocortisone 0.1 mg bid), atenolol (1 to 2 mg/kg per day), and pseudoephedrine(4 mg/kg per day qid). In truly refractory cases, cardiac pacing may be considered.The outlook for syncope depends on the specific diagnosis. Neurocardiac syncope recurs in two thirds of cases, and syncope of other causes has a 90% or greater recurrence rate. Treatment often is effective once the condition is diagnosed. The outlook for many childhood epilepsies is benign. Migraine and narcolepsy usually are controlled by medication. Death can occur unexpectedly in cardiac syncope, and vigorous diagnostic evaluations are warranted whenever palpitations or exercise are associated with syncope.