• Pathophysiology/Etiology: The final common pathway is a transient drop in cerebral blood flow. The main causes are broadly categorized into three groups:

    1. Reflex (Neurally-Mediated) Syncope: The most common cause, especially in younger individuals.
      • Vasovagal: Triggered by stress, fear, pain, or prolonged standing. Involves a cardioinhibitory (vagal-mediated bradycardia) and/or vasodepressor (sympathetic withdrawal leading to vasodilation) response.
      • Situational: Occurs with specific triggers like coughing, micturition, defecation, or swallowing.
      • Carotid Sinus Hypersensitivity: Triggered by pressure on the carotid sinus (e.g., tight collar, shaving).
    2. Orthostatic Hypotension: Drop in BP upon standing (↓ SBP >20 mmHg or DBP >10 mmHg).
      • Causes include volume depletion (hemorrhage, dehydration), medications (e.g., diuretics, alpha-blockers, antihypertensives), and autonomic dysfunction (e.g., Parkinson’s, diabetes).
    3. Cardiac Syncope: Most concerning etiology due to high risk of sudden death.
  • Clinical Presentation:

    • Reflex (Vasovagal): Often preceded by a prodrome (nausea, diaphoresis, warmth, pallor, blurred vision). Typically occurs with a known trigger.
    • Orthostatic: Occurs after standing up. History of volume loss or offending medications.
    • Cardiac: Often sudden onset without a prodrome. Can be precipitated by exertion (suggests outflow obstruction like AS/HCM) or occur at rest (suggests arrhythmia). Family history of sudden cardiac death is a major red flag.
  • Diagnosis:

    • Initial Evaluation (All Pts): Thorough history, physical exam (including orthostatic vitals), and a 12-lead ECG.
    • ECG: Look for arrhythmias, evidence of prior MI (Q waves), ventricular hypertrophy, Brugada syndrome, prolonged/short QT, or WPW (delta wave).
    • Orthostatic Vitals: Positive if SBP drops >20 mmHg, DBP drops >10 mmHg, or HR increases >20 bpm upon standing.
    • Further Testing (if indicated):
      • Echocardiogram: To evaluate for structural heart disease if murmur or ECG abnormality is present.
      • Ambulatory ECG Monitoring (Holter, event recorder): For suspected arrhythmic cause.
      • Tilt-table test: To confirm vasovagal syncope if the diagnosis is uncertain.
      • Electrophysiology Study (EPS): For high-risk patients with suspected tachyarrhythmia.
  • DDx (of Transient Loss of Consciousness):

    • Seizure: Key differentiators include a post-ictal state (confusion, drowsiness), lateral tongue biting, and prolonged tonic-clonic movements. Syncope has a rapid return to baseline.
    • Hypoglycemia: Requires metabolic workup (glucose check).
    • Stroke/TIA: Usually associated with focal neurologic deficits. Vertebrobasilar insufficiency can cause syncope.
    • Mechanical Fall: No true loss of consciousness.
  • Management/Treatment:

    • Reflex (Vasovagal): Patient education on avoiding triggers. Counter-pressure maneuvers (e.g., leg crossing, hand gripping) during prodrome.
    • Orthostatic Hypotension: Replete volume, adjust offending medications, advise slow postural changes.
    • Cardiac: Treat the underlying cause.
      • Arrhythmia: Pacemaker for bradycardia, ICD for life-threatening ventricular arrhythmias.
      • Structural: e.g., Aortic valve replacement for severe AS.
  • Key Associations/Complications (RED FLAGS for Cardiac Syncope):

    • Syncope during exertion.
    • No prodromal symptoms.
    • Abnormal ECG.
    • Personal history of structural heart disease or MI.
    • Family history of sudden cardiac death at a young age.
    • Associated chest pain or shortness of breath.