• Symptom of sudden transient loss of consciousness due to global cerebral hypoperfusion
  • If CPR or cardioversion required, then SCD and not syncope (different prognosis)
  • Presyncope = prodrome of light-headedness without LOC

Etiologies (JACC 2017;70:e39; EHJ 2018;39:1883)

  • Neurocardiogenic (a.k.a. vasovagal, ~25%): ↑ sympathetic tone → vigorous contraction of LV → LV mechanoreceptors trigger ↑ vagal tone (hyperactive Bezold-Jarisch reflex) → ↓ HR (cardioinhib.) and/or ↓ BP (vasodepressor). Cough, deglutition, defecation, & micturition → ↑ vagal tone and thus can be precipitants. Carotid sinus hypersensitivity (exag vagal resp to carotid massage)