• Transient loss of consciousness associated with loss of postural tone
  • Ultimately, it is the lack of oxygen to the brainstem reticular–activating system, which results in a loss of consciousness and postural tone
  • Most commonly, an inciting event causes a drop in cardiac output
  • Cerebral perfusion is re-established by autonomic regulation as well as the reclined posture, which results from the event
  • Accounts for 3% of ED visits

Pregnancy Considerations
  • Pregnant patients frequently experience presyncope or syncope from various causes. 5% of patients experience syncope, 28% experience presyncope throughout their pregnancy
  • Placenta acts as an AV malformation, causing decreased SVR that potentiates orthostatic symptoms
  • Fetus lying on IVC can lead to neurogenic and hypovolemic syncope
  • Pregnant patients at higher risk of DVT/pulmonary embolism (PE), UTI, seizures (preeclampsia), valvular incompetencies. Must exclude these diagnoses in ED evaluation

Geriatric Considerations
  • Elderly with highest incidence as well as increased morbidity
  • >1/3 will have numerous potential causes


  • Neurally mediated syncope:
    • Reflex response causing vasodilatation and bradycardia with resulting cerebral hypoperfusion
    • Vasovagal (common faint):
      • Often incited by pain or fear
      • Prodromal findings are usually present
      • Typically lasts <20 s
      • Tilt-table testing is the gold standard to diagnose
    • Carotid sinus syncope:
      • Cough, sneeze
      • GI stimulation (e.g., defecation)
      • Micturition
  • Orthostatic:
    • Positional changes cause abrupt drop in venous return to heart
    • Volume depletion:
      • Severe dehydration (e.g., vomiting, diarrhea, diuretics)
    • Hemorrhage (see “Hemorrhagic Shock”)
  • Autonomic failure:
    • Diabetic or amyloid neuropathy
    • Parkinson disease
    • Drugs (e.g., β-blockers) and alcohol
  • Cardiac arrhythmias:
    • Typically sudden and without prodromal symptoms
    • Tachydysrhythmia or bradydysrhythmia
    • Inherited syndromes (e.g., long QT syndrome, Brugada syndrome)
    • Pacemaker/implantable cardioverter defibrillator malfunction
  • Structural cardiac or cardiopulmonary disease:
    • Valvular disease (especially aortic stenosis)
    • Hypertrophic cardiomyopathy
    • Acute myocardial infarction
    • Aortic dissection
    • Pericardial tamponade
  • Pulmonary embolus
  • Neurologic:
    • Transient spike in intracranial pressure that exceeds cerebral perfusion pressure
    • Postsyncopal headache is almost universal
    • May be presentation of a subarachnoid hemorrhage
  • Cerebrovascular steal syndromes

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