A 58-year-old woman with permanent atrial fibrillation and a history of acute myocardial infarction 2 months ago (ejection fraction 35%) presents with persistent symptoms despite adequate rate control with metoprolol. She requires rhythm control. Which drug is the preferred choice for rhythm control in this patient?

Explanation

## Rhythm Control in Atrial Fibrillation with Reduced Ejection Fraction **Key Point:** Amiodarone is the only antiarrhythmic drug safe for rhythm control in patients with AF and reduced ejection fraction (EF ≤40%), particularly post-MI. Class IC agents (flecainide, propafenone) and sotalol are contraindicated due to increased mortality risk. ### Mechanism of Amiodarone Amiodarone is a Class I, II, III, and IV antiarrhythmic with: - **Class I effect:** Sodium channel blockade (slows conduction) - **Class II effect:** Beta-blockade (AV nodal slowing) - **Class III effect:** Potassium channel blockade (prolongs APD and QT) - **Class IV effect:** Calcium channel blockade (AV nodal effects) This multi-channel action makes it uniquely effective and relatively safe in structural heart disease. ### Antiarrhythmic Safety in Reduced EF | Drug | Class | EF ≤40% Safe? | Mechanism of Risk | |------|-------|---------------|-------------------| | **Amiodarone** | I, II, III, IV | **Yes** | Multi-channel; no mortality increase | | **Flecainide** | Ic | No | CAST trial: increased mortality in post-MI | | **Propafenone** | Ic | No | CAST trial: increased mortality in post-MI | | **Sotalol** | III (+ beta-block) | No | Torsades de pointes risk; mortality increase in HF | | **Dofetilide** | III | Relative | QT prolongation; requires monitoring | **High-Yield:** The **CAST trial** (1989) demonstrated that Class IC antiarrhythmics (flecainide, encainide) increase mortality in post-MI patients with reduced EF, even if they suppress arrhythmias. This landmark finding changed AF management forever. **Warning:** ~~Flecainide and propafenone are safe in AF~~ — they are contraindicated in structural heart disease and post-MI due to proarrhythmic effects and mortality risk. ### Clinical Decision Algorithm ```mermaid flowchart TD A[AF Requiring Rhythm Control]:::outcome --> B{Structural Heart Disease or EF ≤40%?}:::decision B -->|No| C[Class IC or III agents]:::action B -->|Yes| D{Recent MI or Cardiomyopathy?}:::decision C --> E[Flecainide, propafenone, or sotalol]:::outcome D -->|Yes| F[Amiodarone ONLY]:::action D -->|No| G[Amiodarone preferred; dofetilide alternative]:::action F --> H[Monitor EFTs, TFTs, chest X-ray]:::outcome ``` ### Amiodarone: Toxicity Profile **Organ-specific toxicities** (require baseline and periodic monitoring): - **Pulmonary:** Interstitial pneumonitis, pulmonary fibrosis (1–17%) - **Hepatic:** Cirrhosis, hepatitis (rare) - **Thyroid:** Hyper- or hypothyroidism (15–20%) - **Ocular:** Corneal microdeposits (asymptomatic) - **Cardiac:** Bradycardia, AV block, torsades (rare due to Class II/III balance) **Monitoring:** Baseline and 6-monthly LFTs, TFTs, chest X-ray; ECG for QT prolongation. **Clinical Pearl:** Despite its toxicity, amiodarone is the safest antiarrhythmic in structural heart disease because it does NOT increase mortality — a unique property among Class I agents.