## Drug of Choice for Sustained Ventricular Tachycardia **Key Point:** Amiodarone is the most effective and preferred antiarrhythmic for suppression of sustained ventricular tachycardia, particularly in patients with structural heart disease (post-MI). ### Why Amiodarone? 1. **Broad spectrum action** — Class III agent with properties of all four Vaughan-Williams classes 2. **Superior efficacy** — Highest success rate in terminating and preventing recurrent VT 3. **Structural heart disease** — Safe and effective in post-MI patients, unlike Class IC agents (which increase mortality in this population) 4. **Electrophysiologic properties** — Prolongs refractoriness in all cardiac tissues, suppressing re-entrant circuits ### Antiarrhythmic Classification & Comparative Efficacy | Drug | Class | Mechanism | VT Efficacy | Post-MI Safety | Notes | |------|-------|-----------|-------------|-----------------|-------| | **Amiodarone** | III (+ I, II, IV) | K^+^ channel blocker + others | **Highest** | **Safe** | Preferred for structural disease | | Procainamide | IA | Na^+^ channel blocker | Moderate | Moderate | Lupus risk, requires monitoring | | Sotalol | III + β-blocker | K^+^ channel blocker | Moderate | Moderate | QT prolongation risk | | Flecainide | IC | Na^+^ channel blocker | Moderate | **Contraindicated** | CAST trial: ↑ mortality post-MI | **High-Yield:** The CAST (Cardiac Arrhythmia Suppression Trial) demonstrated that Class IC antiarrhythmics (flecainide, encainide) increase mortality in post-MI patients with reduced ejection fraction — a landmark finding that eliminated them as first-line agents in structural heart disease. **Clinical Pearl:** Although amiodarone carries risks of thyroid, pulmonary, and hepatic toxicity with chronic use, these are acceptable trade-offs for its superior efficacy in life-threatening arrhythmias in patients with structural disease. ### Mechanism of Amiodarone in VT Suppression ```mermaid flowchart TD A[Sustained VT - Re-entrant Circuit]:::outcome --> B{Antiarrhythmic Choice}:::decision B -->|Structural heart disease| C[Amiodarone]:::action B -->|No structural disease| D[Sotalol or Procainamide]:::action C --> E[Prolongs refractoriness]:::action C --> F[Blocks Na+ and K+ channels]:::action E --> G[Breaks re-entrant circuit]:::outcome F --> G G --> H[VT suppression achieved]:::outcome ``` **Mnemonic:** **ABCD** of amiodarone — **A**ntiarrhythmic, **B**eta-blocker, **C**alcium channel blocker, **D**isopyramide-like properties (all four classes).
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