Syncope

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.
   • Arrhythmias (most common cardiac cause): Bradyarrhythmias (AV block, sinus node dysfunction) or tachyarrhythmias (VT, SVT).
   • Structural Heart Disease: Aortic stenosis, hypertrophic cardiomyopathy (HCM), MI, massive PE, cardiac tamponade.

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.