Syncope is defined as the sudden, transient loss of consciousness and may be the result of a variety of cardiac and noncardiac conditions. Presyncope is a feeling of impending syncope without true loss of consciousness.
Cardiovascular causes are responsible for the vast majority of cases and produce loss of consciousness by means of a drop in blood pressure with resultant bilateral cortical or brain stem hypoperfusion. Cerebrovascular disease is an uncommon cause of syncope unless bilateral carotid artery disease or vertebrobasilar disease is present. The most important aspect of the approach to the patient with syncope is in obtaining a thorough history, both from the patient as well as from any witnesses to the episode. The conditions during which a syncopal occurs may suggest the etiology.

For instance, syncope that occurs on arising from a lying or sitting position suggests orthostasis. Exercise-induced syncope suggests obstructive cardiac disease, such as aortic or mitral valve stenosis, or hypertrophic cardiomyopathy. Syncope during straining, coughing, or micturition is the result of Valsalva-induced decrease in venous return. A history of palpitations preceding the event suggests an arrhythmic cause. Syncope that occurs during emotional stress suggests a vasovagal episode. Certain features may suggest a noncardiac cause, including incontinence or tonic-clonic movements, which suggest seizure. Patients who suffer a cardiac syncopal episode usually regain consciousness rapidly

The physical examination of a patient with syncope should include evaluation of orthostatic changes in the heart rate and blood pressure, a thorough cardiac examination to exclude significant murmurs, a neurologic examination, and carotid sinus massage when the history suggests carotid sinus sensitivity as the diagnosis.

A 12 lead ECG should be obtained and may be diagnostic of the etiology of syncope(e.g., complete heart block) or reveal abnormalities that warrant further evaluation.