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A.J. Larner


February 27, 2014: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.


Chapter re-evaluated and minor changes made.

Updated on 28 Nov 2012. The previous version of this content can be found here.
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date: 28 April 2017

Syncope is the commonest identified cause of transient loss of consciousness, being ten times more frequent than epilepsy. It is a consequence of cerebral underperfusion due to reduced cardiac output, often related to reduced venous return due to decreased peripheral vascular resistance, with pooling of blood volume in dependent body parts.


These include (1) neurally mediated—vasovagal; carotid sinus; situational, e.g. cough syncope; (2) orthostatic (postural) hypotension—autonomic failure; drug-induced; volume depletion; (3) cardiac arrhythmia; (4) cardiac/vascular structural disease—e.g. aortic stenosis.

Diagnosis, prognosis, investigations, and treatment

Diagnosis is clinical, based on history of the circumstances of the event obtained from the patient and reliable eyewitnesses; there is no other diagnostic test. In most patients, particularly those under 45 years of age, the condition is benign and self-limiting, with an excellent prognosis, requiring little investigation beyond physical examination and ECG to exclude heart disease. Cardiac causes of syncope may require specific treatment.

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