Syncope refers to loss of consciousness (LOC) associated with loss of postural tone that is sudden in onset, transient, is followed by spontaneous recovery, 1,2 and is with no residual neurologic deficit. Premonitory symptoms such as light-headedness, nausea, yawning, or sweating are common. Most causes of syncope are benign except in a small subset of a population where it presages a life-threatening event. The word pre-syncope is often used to describe the occurrence of premonitory symptoms of syncope but without LOC.
EpidemiologySyncope is relatively common. It affects 3% of men and 3.5% of women at some point in life. Elderly are more commonly affected, especially aged > 75 years (6%). However, any age can be affected with syncope in the presence or absence of other medical problems. Young adults commonly have noncardiac causes whereas cardiac syncope is more frequent with advancing age. Syncope in pediatric populations is rare and warrants prompt, detailed evaluation.
PathophysiologyNormal blood flow to the brain is 50 to 65 mL/100 g of brain tissue with a total flow of 750 to 900 mL/min approximately, which is 15% of cardiac output and only 2% of body weight. Syncope results from global cerebral hypoperfusion and low systemic blood pressure (BP) 3,4 (►Fig. 1).