A 72-year-old woman with a history of myocardial infarction 2 months ago presents with recurrent episodes of ventricular tachycardia (VT). She is haemodynamically stable during the episodes. Her left ventricular ejection fraction (LVEF) is 35%. Baseline ECG shows prolonged QT interval (480 ms). She is already on a beta-blocker and ACE inhibitor. Which antiarrhythmic agent would be most appropriate for long-term management of her recurrent VT?

## Clinical Context: Post-MI Ventricular Arrhythmia The patient has: - **Recurrent VT** in the setting of **prior MI** (scar-related reentry) - **Reduced LVEF (35%)** — high-risk substrate for sudden cardiac death - **Prolonged QT (480 ms)** — baseline risk for proarrhythmia - **Haemodynamic stability** — allows medical management (not ICD alone) ## Why Amiodarone is Superior **Key Point:** In post-MI VT with reduced LVEF and baseline QT prolongation, **amiodarone is the antiarrhythmic of choice** because it combines efficacy with a **low proarrhythmic risk** and **negative inotropic tolerance**. **High-Yield:** Amiodarone's unique profile in this setting: 1. **Broad spectrum** (Class I, II, III, IV) — suppresses multiple arrhythmia mechanisms 2. **Lowest proarrhythmic risk** among antiarrhythmics (despite Class III effect) 3. **Negative inotropic effect is minimal** — critical in reduced EF 4. **No QT-dependent torsades risk** — paradoxically safe despite QT prolongation 5. **Post-MI evidence base** — CAMIAT, EMIAT trials showed mortality benefit ## Comparative Analysis of Options | Agent | Class | Mechanism | Post-MI VT | EF <40% | QT Risk | Issue in This Patient | |-------|-------|-----------|-----------|---------|---------|----------------------| | **Amiodarone** | I+II+III+IV | Multi-channel blocker | ✓ Excellent | ✓ Safe | ✓ Low | None — ideal choice | | Sotalol | II+III | Beta-blocker + K⁺ channel | Moderate | Caution | ⚠ High | Prolongs QT further; torsades risk | | Flecainide | IA | Na⁺ channel blocker | ✗ Contraindicated | ✗ Dangerous | Neutral | **CAST trial**: ↑ mortality post-MI | | Disopyramide | IA | Na⁺ channel blocker | ✗ Contraindicated | ✗ Dangerous | ⚠ Moderate | Negative inotrope; worsens HF | **Clinical Pearl:** The **CAST trial (1989)** demonstrated that Class I antiarrhythmics (flecainide, encainide) **increase mortality** in post-MI patients with reduced EF, even if they suppress arrhythmias. This landmark finding eliminated Class IA/IB agents from post-MI VT management. **Warning:** Sotalol and dofetilide prolong QT and carry torsades risk, especially problematic when baseline QT is already 480 ms. Amiodarone prolongs QT but does **not** cause torsades — a paradox explained by its simultaneous Na⁺ and K⁺ channel blockade. ## Mechanism & Evidence ```mermaid flowchart TD A[Post-MI VT + reduced EF + prolonged QT]:::outcome --> B{Haemodynamically stable?}:::decision B -->|Yes| C[Amiodarone first-line]:::action C --> D[Multi-channel blockade]:::action D --> E[Suppresses reentrant VT]:::action E --> F[Low proarrhythmic risk]:::action F --> G[Mortality benefit proven]:::outcome B -->|No| H[ICD + amiodarone]:::action I[Avoid Class IA/IB post-MI]:::urgent --> J[CAST trial evidence] ``` **Dosing:** Amiodarone loading 800 mg/day × 1 week, then 600 mg/day × 1 week, then 400 mg/day maintenance. [cite:Harrison 21e Ch 297; Antman & Braunwald Post-MI Management]