Description

• Transient loss of consciousness characterized by unresponsiveness, loss of postural tone, and spontaneous recovery; usually caused by cerebral hypoxemia
• System(s) affected: Cardiovascular; Nervous

Epidemiology

• Up to 20% of adults will have ≥1 episode by age 75; 15% of children <18 years of age
• Accounts for 1–6% of hospital admissions and ~3% of emergency room visits
• Epidemiological study showed yearly prevalence of fainting spells resulting in medical evaluation was 9.5/1,000 inhabitants (1).

Prevalence
In institutionalized elderly (>75 years), 6%

Risk Factors

• Heart disease
• Dehydration
• Drugs:
  • Antihypertensives
  • Vasodilators (including calcium channel blockers, ACE inhibitors, and nitrates)
  • Phenothiazines
  • Antidepressants
  • Antiarrhythmics
  • Diuretics

Genetics
Specific cardiomyopathies and arrhythmias may be familial (i.e., long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy).

General Prevention

See “Risk Factors.”

Pathophysiology

• In some cases, vagal response leads to decreased heart rate.
• Systemic hypotension secondary to decreased cardiac output and/or systemic vasodilation leads to a drop in cerebral perfusion and resulting loss of consciousness.

Etiology

• Cardiac: Obstruction to outflow:
  • Aortic stenosis
  • Hypertrophic cardiomyopathy
  • Pulmonary embolus
  • Anomalous coronary artery origin resulting in cardiac ischemia
• Cardiac arrhythmias:
  • Sustained ventricular tachycardia (VT)
  • Supraventricular tachycardia (atrial fibrillation, atrial flutter, re-entrant SVT)
  • 2nd- and 3rd-degree AV block
  • Sick-sinus syndrome
  • Pacing-induced infranodal block
  • H-V interval >100 ms
• Noncardiac:
  • Reflex-mediated vasovagal (neurocardiogenic/neurally mediated), situational (micturition, defecation, cough, hair combing)
  • Orthostatic hypotension
  • Drug-induced
  • Neurologic: Seizures; transient ischemic attack (can in theory cause syncope, but presentation usually markedly clinically different from pure syncope)
  • Carotid sinus hypersensitivity
  • Psychogenic

Commonly Associated Conditions

See “Etiology.”