Syncope is a loss of consciousness and postural tone caused by diminished cerebral blood flow. By age 75 approximately 5-20% of adults will have one or more episodes of syncope. It accounts for about 1% of hospital admissions and about 3% of emergency room visits. Its annual incidence in the institutionalized elderly is about 6%.
Syncope can be caused by an obstruction to cardiac outflow: Aortic stenosis, Hypertrophic cardiomyopathy, and Pulmonary embolus. Syncope can be associated with cardiac arrhythmias: Ventricular tachycardia, Sick sinus syndrome, 2nd and 3rd degree AV block.
Non-cardiac causes of syncope include: Vasovagal, situational (micturition, defecation, cough); Orthostatic hypotension; Drug induced (see below); Seizures; Transient ischemic attack; Carotid sinus; and Psychogenic.
Patients with heart disease are at higher risk for syncope. Patients taking following drugs: Antihypertensives, Vasodilators (including calcium channel blockers, ACE inhibitors, and nitrates), Phenothiazines, Antidepressants, Antiarrhythmics, and Diuretics.
Lab tests are rarely helpful. Less than 2% have hyponatremia, hypocalcemia, hypoglycemia or renal failure causing seizures.
An echocardiogram and cardiac catheterization may be ordered if the history and physical is suggestive of ischemic, valvular or congenital heart disease. If CNS disease suspected, an EEG, head CT, head MRI may be ordered.
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