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Syncope in adults: Clinical manifestations and diagnostic evaluation

David Benditt, MD
Section Editors
Peter Kowey, MD, FACC, FAHA, FHRS
Robert S Hockberger, MD, FACEP
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).

Syncope is only one on the many potential causes of TLOC. Examples of non-syncopal causes of TLOC, or apparent TLOC, include seizure disorders, traumatic brain injury (ie, concussion), intoxications, metabolic disturbances, and conversion disorders (ie, psychogenic "pseudo-syncope" or "pseudo-seizures"). Distinguishing these conditions from true syncope may be challenging, but it is crucial in order to determine appropriate management.

True syncope itself has many possible causes (table 1). Consequently, after the syncopal event has resolved and the patient is hemodynamically stable, the essential next step is establishing the etiology in order to initiate an appropriate diagnostic and treatment strategy to prevent future events as well as to determine prognosis. The initial evaluation of suspected syncope relies heavily on obtaining of a comprehensive history, performing a physical examination (which may include careful carotid sinus massage in older patients), and reviewing an electrocardiogram; these steps should guide the subsequent diagnostic evaluation and help limit unnecessary testing and treatment.

Issues relating to the evaluation of syncope in adults will be reviewed here. The approach to the adult patients with syncope in the emergency department, as well as the pathogenesis, etiology, and management of syncope in adults, are discussed elsewhere. (See "Approach to the adult patient with syncope in the emergency department" and "Syncope in adults: Epidemiology, pathogenesis, and etiologies" and "Reflex syncope in adults: Clinical presentation and diagnostic evaluation" and "Syncope in adults: Management".)

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Literature review current through: Nov 2017. | This topic last updated: Aug 02, 2017.
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