A 58-year-old man with a history of myocardial infarction presents with recurrent episodes of ventricular tachycardia. His cardiologist is considering antiarrhythmic therapy. Which class of antiarrhythmic drugs is most commonly used as first-line therapy for ventricular arrhythmias in the post-MI setting?

## Class II Antiarrhythmics in Post-MI Ventricular Arrhythmias **Key Point:** Beta-blockers (Class II antiarrhythmics) are the most commonly used first-line agents for ventricular arrhythmias in the post-MI setting, particularly for prevention of sudden cardiac death. ### Why Class II is Preferred **High-Yield:** Beta-blockers provide: 1. **Reduction in sudden cardiac death** — proven mortality benefit in post-MI patients 2. **Sympathetic suppression** — ventricular arrhythmias in post-MI are often triggered by catecholamine surge 3. **Cardioprotection** — reduce myocardial oxygen demand and improve diastolic filling 4. **Safety profile** — well-tolerated with established long-term efficacy **Clinical Pearl:** The CIBIS, MERIT-HF, and COPERNICUS trials demonstrated that beta-blockers reduce mortality in post-MI and heart failure patients, making them the cornerstone of therapy. ### Comparison of Antiarrhythmic Classes in Post-MI Setting | Class | Agent | Mechanism | Post-MI Role | Limitation | | --- | --- | --- | --- | --- | | **II** | Metoprolol, Carvedilol, Bisoprolol | β-adrenergic blockade | **First-line** | Bradycardia, AV block | | I-A | Quinidine, Procainamide | Na^+^ block + K^+^ block | Avoided | **Proarrhythmic** (CAST trial) | | I-B | Lidocaine | Na^+^ block (short QT) | Acute VT/VF only | Short duration | | I-C | Flecainide, Propafenone | Strong Na^+^ block | **Contraindicated** | **Increased mortality** (CAST) | | III | Amiodarone, Sotalol | K^+^ channel block | Second-line | Toxicity, drug interactions | | IV | Verapamil, Diltiazem | Ca^2+^ channel block | SVT only | Negative inotrope (avoid in HF) | **Warning:** Class I-C drugs (flecainide, propafenone) are **contraindicated** in post-MI patients — the CAST trial showed increased mortality despite suppression of arrhythmias ("antiarrhythmic paradox"). ### Mechanism of Beta-Blocker Efficacy **Mnemonic: BETA** — **B**locking catecholamine effects, **E**nhancing diastolic filling, **T**herapeutic AV nodal delay, **A**ntiarrhythmic via sympathetic suppression. 1. **Sympathetic suppression** — blocks β₁-receptors on cardiac myocytes 2. **Reduced automaticity** — decreases spontaneous depolarization in ectopic foci 3. **Slowed conduction** — prolongs AV nodal refractoriness 4. **Reduced oxygen demand** — decreases ischemic burden **High-Yield:** Beta-blockers are indicated for **all post-MI patients** unless contraindicated (cardiogenic shock, severe bradycardia, high-degree AV block). [cite:Harrison 21e Ch 297]