Syncope is an episode of sudden loss of consciousness associated with loss of postural tone followed by spontaneous recovery. It is a common reason for emergency room evaluations and accounts for 740,000 emergency room visits per year in the United States.1 Syncope can result from a variety of different mechanisms including neurologic, cardiovascular, orthostatic, and metabolic etiologies. Historical details regarding the episodes and thorough knowledge regarding a patient's concomitant medical problems and medications are essential in determining the cause for a particular patient.
Incidence and Age of Onset
Although syncope may occur in all age groups, the incidence varies greatly by age. The lifetime cumulative incidence of syncope has been reported to be 35%, with a high incidence in the pediatric population, in whom neurocardiogenic syncope is the most common etiology.2 Of note, 37% of patients in this study never sought medical attention for syncope, suggesting that both emergency room data and studies relying on medical reports of syncope likely underestimate the true incidence of syncope. The incidence of syncope in children and adolescents seeking medical attention has been reported to be between 71.9 and 125.8 per 100,000 over a 5-year period.3 Individual studies have generally evaluated specific age groups, rather than a broad pediatric-to-elderly range. However, these data suggest that there may be two peaks in incidence rates, one occurring between the ages of 15 and 19 years,2,3 and another occurring in advanced age. The incidence rate in adulthood has been reported to be 6.2 per 1000 person-years, with a greater incidence rate seen in those older than 70.4 For the institutionalized elderly, the annual incidence rate has been reported to be as high as 6%.5
For all age groups, neurocardiogenic syncope appears to be the most common etiology. In a group of 822 adult patients (mean age 65.8 years) with syncope, 21.2% had neurocardiogenic syncope, 9.5% had cardiac syncope, 9.4 % had orthostatic syncope, and 36.6% had syncope of undetermined etiology.4
In most series, women are reported to experience syncope more commonly than men.2,3,6,7 This gender difference is reported in both younger and older populations. The reason for this difference is not clear. Although neurocardiogenic syncope is reported to be the most common cause of syncope in both the elderly and young populations in both sexes, men are more likely than women to be diagnosed with a cardiac etiology for syncope and to experience a subsequent cardiac event, such as myocardial infarction, recurrent cardiac syncope, or sudden death.7,8
Associated Medical Syndromes and Natural History
Syncope can be classified into four different categories: cardiovascular, neurally mediated, orthostatic, and metabolic. Such a classification is important not only ...