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Syncope is a sudden, temporary loss of consciousness and postural tone caused by transient global cerebral hypoperfusion, followed by spontaneous recovery. It affects up to 3% of emergency department visits and has a wide range of causes from benign vasovagal episodes to life-threatening cardiac arrhythmias. Proper evaluation is crucial to distinguish syncope from other causes of altered consciousness and identify patients at risk for adverse outcomes.
Syncope results from inadequate cerebral blood flow, typically requiring a 20-50% reduction in cerebral perfusion for 6-8 seconds to cause loss of consciousness. The underlying mechanisms include decreased cardiac output (structural heart disease, arrhythmias), reduced venous return (orthostatic hypotension, volume depletion), or inappropriate vasodilation with or without bradycardia (neurally mediated syncope). Reflex syncope involves complex interactions between the autonomic nervous system, baroreceptors, and cardiopulmonary receptors leading to paradoxical vasodilation and bradycardia.
The diagnostic approach focuses on detailed history-taking to identify precipitating factors, prodromal symptoms, and associated conditions, along with cardiovascular examination and orthostatic vital signs. Risk stratification is essential, with cardiac syncope carrying higher mortality risk than neurally mediated causes, requiring evaluation for structural heart disease and arrhythmias through ECG and potentially echocardiography or cardiac monitoring. The absence of cardiac disease and presence of typical triggers (prolonged standing, pain, emotional stress) with prodromal symptoms suggests benign vasovagal syncope.