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Syncope in adults: Epidemiology, pathogenesis, and etiologies

David Benditt, MD
Section Editor
Peter Kowey, MD, FACC, FAHA, FHRS
Deputy Editor
Brian C Downey, MD, FACC


Syncope is a clinical syndrome in which transient loss of consciousness (TLOC) is caused by a period of inadequate cerebral nutrient flow, most often the result of an abrupt drop of systemic blood pressure. Typically, the inadequate cerebral nutrient flow is of relatively brief duration (8 to 10 seconds) and, in syncope, is by definition spontaneously self-limited.

Loss of postural tone is inevitable with loss of consciousness, and consequently syncope usually is associated with collapse, which may trigger injury due to a fall (such as may occur if the person is standing) or other type of accident (eg, if syncope occurs while driving). Recovery from true syncope is usually complete and rapid, with episodes rarely lasting more than a minute or two. Longer periods of real or apparent loss of consciousness suggest that the event is not syncope or is not syncope alone (eg, syncope resulting in a head injury, thereby prolonging the event).

True syncope itself has many possible causes (table 1). Syncope, however, is only one of the many potential causes of TLOC. Examples of nonsyncopal causes of TLOC, or apparent TLOC, include seizure disorders, traumatic brain injury (eg, concussion), intoxications, metabolic disturbances, and conversion disorders (eg, psychogenic "pseudosyncope" or "pseudoseizures"). Distinguishing these conditions from true syncope may be challenging, but it is crucial in order to determine appropriate management. In much of the published literature, it is not possible to distinguish true syncope from other TLOC events.

The epidemiology, pathogenesis, and etiologies of syncope will be reviewed here. The clinical manifestations, diagnostic evaluation, and management of syncope is discussed in detail separately. (See "Syncope in adults: Clinical manifestations and diagnostic evaluation" and "Syncope in adults: Management".)


Syncope is a common clinical problem, with a lifetime prevalence in the population as a whole of approximately 20 percent [1,2]. In one of the largest epidemiologic studies that evaluated the incidence and prognosis of syncope, 822 of 7814 men and women (11 percent) who were followed for an average of 17 years as part of the Framingham Heart Study reported an apparent syncopal episode [3]. The incidence of syncope increases with age, with a sharp rise after age 70 years (figure 1). The increased risk of syncope in older adult patients appears to be due to age- and disease-related abnormalities that impair the ability to respond to physiologic stresses that would ordinarily not cause syncope [4].

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Literature review current through: Nov 2017. | This topic last updated: Aug 10, 2017.
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