Etiologies-syncope

• Vasovagal (a.k.a. neurocardiogenic, ~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) is related disorder.

• Orthostatic hypotension (~10%)

  • hypovolemia/diuretics, deconditioning; vasodilat. (esp. if combined w/ ⊖ chronotropes)
  • autonomic neuropathy
    • 1° = Parkinson’s, MSA/Shy-Drager, Lewy body dementia, POTS (dysautonomia in the young);
    • 2° = DM, EtOH, amyloidosis, CKD (JACC 2018;72:1294)

• Cardiovascular (~20%, more likely in men than women)

  • Arrhythmia ( ~15% ):
    • challenging to dx because often transient
    • Bradyarrhythmias:
      • SB, Sick sinus syndrom (SSS), high-grade AV block, ⊖ chronotropes, PPM malfunction
    • Tachyarrhythmias:
      • VT, SVT (syncope rare unless structural heart disease or WPW)
  • Mechanical (5%)
    • Endocardial/Valvular: critical AS, MS, PS, prosthetic valve thrombosis, myxoma
    • Myocardial: outflow obstruction from HCMP (or VT); pericardial: tamponade
    • Vascular: PE (in ~25% w/o alt dx; NEJM 2016;375:1524), PHT, AoD, ruptured AAA

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• Neurologic (~10%):
  • vertebrobasil insuff, cerebrovasc dissection, SAH, TIA/CVA
• Misc. causes of LOC (but not syncope):
  • seizure,
  • ↓ glc,
  • hypoxia,
  • narcolepsy,
  • psychogenic