Syncope is a topic covered in the 5-Minute Clinical Consult.

To view the entire topic, please or purchase a subscription.

Medicine Central™ is a quick-consult mobile and web resource that includes diagnosis, treatment, medications, and follow-up information on over 700 diseases and disorders, providing fast answers—anytime, anywhere. Explore these free sample topics:

Medicine Central

-- The first section of this topic is shown below --



  • Transient loss of consciousness characterized by unresponsiveness, loss of postural tone, and spontaneous recovery; usually brief and caused by cerebral hypoperfusion
  • System(s) affected: cardiovascular, nervous


  • Overall incidence is 6.2/1,000 patient-years.
  • Annual incidence of fainting spells resulting in medical evaluation was 9.5/1,000 inhabitants.
  • Accounts for 1–3% of emergency room visits and 1% of hospital admissions
  • There is an increased incidence after the age of 70 years, and annual incidence in institutionalized elderly (>75 years of age) is 7%.

  • Approximately 20% 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 resulting loss of consciousness.
  • Cardiac
    • Obstructions to outflow
      • Aortic stenosis
      • Hypertrophic cardiomyopathy: most common cause of sudden cardiac death during exercise in young athletes
      • Pulmonary embolus
      • Pulmonary hypertension
    • Cardiac arrhythmias
      • Sustained ventricular tachycardia (VT)
      • Supraventricular tachycardia (SVT) (atrial fibrillation, atrial flutter, reentrant SVT)
      • Torsades de pointes (TdP)
      • Bradyarrhythmia
        • 2nd- and 3rd-degree AV block
        • Sick sinus syndrome
  • Noncardiac
    • Reflex-mediated vasovagal (neurally mediated syncope [NMS]/neurocardiogenic): inappropriate vasodilation leading to neurally mediated systemic hypotension and decreased cerebral blood flow, situational (micturition, defecation, cough, pain, emotions, hair combing)
    • Orthostatic hypotension: Consider volume depletion, pregnancy, anemia, medications.
    • Drug/alcohol induced
    • Primary autonomic failure: pure autonomic failure, Parkinson
    • Secondary autonomic failure: diabetes, amyloidosis
    • Carotid sinus hypersensitivity
  • NMS is most common cause in adult cases.
  • Vast majority of pediatric cases represent benign alterations in vasomotor tone.
  • Strokes, seizures, and psychogenic nonepileptic seizures may mimic syncope but are a distinct diagnosis.

Specific cardiomyopathies and arrhythmias may be inherited (e.g., long QT syndrome, catecholaminergic polymorphic VT, Brugada syndrome, hypertrophic cardiomyopathy). Primary and secondary autonomic failure syndromes and NMS may also have genetic links.

Risk Factors

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

General Prevention

See “Risk Factors.”

Commonly Associated Conditions

See “Etiology and Pathophysiology.”

-- To view the remaining sections of this topic, please or purchase a subscription --