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Pathogenesis and etiology of syncope

Brian Olshansky, MD
Section Editor
Leonard I Ganz, MD, FHRS, FACC
Deputy Editor
Brian C Downey, MD, FACC


Syncope is the abrupt and transient loss of consciousness associated with absence of postural tone, followed by complete and usually rapid spontaneous recovery. This symptom is alarming for the individual, witnesses, family, and physicians. Although syncope can be a harbinger of a multitude of disease processes and can mimic the appearance of a cardiac arrest, it is most often benign and self-limited. Nevertheless, injuries associated with syncopal attacks occur in about one-third of patients, and recurrent episodes can be psychologically devastating. In addition, syncope can be a premonitory sign of cardiac arrest, especially in patients with organic heart disease.

The cause of syncope is often not obvious, and individuals at highest risk for sudden death can be difficult to detect (table 1) [1]. It is important to recognize that syncope and cardiac arrest are two different entities that must be distinguished from each other in order to accurately assess future outcome and prognosis. Patients in whom cardiopulmonary resuscitation or electric or pharmacologic cardioversion have been required should be labeled as having cardiac arrest and not as having syncope. These two diagnostic entities are inextricably intertwined, however, since patients with cardiac syncope have a high incidence of subsequent cardiac arrest (approximately 24 percent) [2].

The epidemiology, pathogenesis, and etiology of syncope will be reviewed here. The evaluation and management of this disorder are discussed separately. (See "Syncope in adults: Clinical manifestations and diagnostic evaluation" and "Syncope in adults: Management".)

The pathogenesis and etiology of syncope are the same as that for presyncope, which is the prodromal symptom of fainting. Such patients usually present with symptoms of dizziness. (See "Approach to the patient with dizziness".)


Syncope is a common clinical problem [3]. 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 a syncopal episode [4]. The incidence of syncope increased with age, with a sharp rise at age 70 years (figure 1). The increased risk of syncope in elderly 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 [5].


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Literature review current through: May 2017. | This topic last updated: Oct 26, 2015.
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