- Approximately 20–35% of adults report ≥1 episode during their lifetime; 15% of children <18 years of age
- The prevalence in institutionalized elderly (>75 years of age) is 23%.
Etiology and Pathophysiology
Systemic hypotension secondary to decreased cardiac output and/or systemic vasodilation leads to a drop in cerebral perfusion and resultant loss of consciousness.
- Cardiac obstructions to outflow (e.g., pulmonary embolus [PE], hypertrophic cardiomyopathy, aortic stenosis)
- Cardiac arrhythmias
- Reflex-mediated vasovagal (neurally mediated syncope [NMS]): inappropriate vasodilation leading to neurally mediated systemic hypotension and decreased cerebral blood flow; situational (micturition, defecation, cough, pain, emotions, hair combing)—most common cause in adult cases
- Orthostatic hypotension (OHT): volume depletion, pregnancy, anemia, medications
- Drug/alcohol induced
- Primary autonomic failure: pure autonomic failure, Parkinson
- Secondary autonomic failure: diabetes, amyloidosis
- Carotid sinus hypersensitivity
- Vast majority of pediatric cases represent benign alterations in vasomotor tone.
- Heart disease (acquired or structural)
- Many drugs (e.g., antihypertensives, antiarrhythmics, diuretics)
- Presence of a primary autonomic degenerative disorder
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