Syncope or fainting is a symptom complex consisting of a brief loss of consciousness associated with an inability to maintain postural tone that spontaneously resolves without medical intervention. Syncope accounts for approximately 1% to 2% of ED visits each year and up to 6% of hospital admissions.1-3 In the Framingham Heart Study, 7814 patients were followed for 17 years, and 10.5% reported syncope.4 Syncope in the preceding year is the best predictor of recurrence.5 It can affect the young and the old, with the elderly having the greatest morbidity.6 Near-syncope, a premonition of fainting without loss of consciousness, shares the same basic pathophysiologic process as syncope and may carry the same risks.7,8
The final common pathway of syncope is the same regardless of the underlying cause: about 10 seconds of complete disruption of blood flow or nutrient delivery to both cerebral cortices or to the brainstem reticular activating system, or reduction of cerebral perfusion by 35% to 50%. Most commonly, an inciting event causes a drop in cardiac output, which decreases oxygen and substrate delivery to the brain. Less commonly, vasospasm reduces CNS blood flow. Cerebral perfusion and consciousness are restored by the supine position, the response of autonomic autoregulatory centers, or restoration of a perfusing cardiac rhythm.
The causes of syncope are numerous (Table 50-1). The major causes of syncope identified in the Framingham Heart Study were vasovagal (reflex mediated, 21%), cardiac (10%), orthostatic (9%), medication related (7%), neurologic (4%), and unknown (37%).4 In most studies, even with exhaustive patient evaluation, the cause remains unknown in about 40% of individuals.9,10 After ED investigation, the unknown proportion may be 50% to 60%. Diagnosis is important, because each diagnostic classification carries with it prognostic risk. In the Framingham study, cardiac syncope doubled the risk of death, neurologic syncope increased the risk of death by 50%, and syncope of unknown cause increased the risk of death by 30%, compared to the general population cohort of the study. Individuals with neurally/reflex-mediated or vasovagal syncope had no increased risk of death compared with the general population cohort.4
Table 50-1 Causes of Syncope |Favorite Table|Download (.pdf)
Table 50-1 Causes of Syncope
Structural cardiopulmonary disease
Valvular heart disease
Congenital heart disease
Short or long QT syndromes
Sinus node disease
Second- or third-degree heart block
Torsade de pointes
Atrial fibrillation or flutter
Carotid sinus syndrome
Orthostatic hypotension (see text)
Transient ischemic attacks
Medications (Table 50-2)
Breath holding (pediatric)*
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