Description

• 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

• 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

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

Etiology

• 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