Which antiarrhythmic drug blocks both sodium and potassium channels and is classified as a Class IA agent?

Explanation

## Antiarrhythmic Classification by Vaughan-Williams **Key Point:** Class IA antiarrhythmics block both fast sodium channels (Phase 0 depression) AND potassium channels (Phase 3 prolongation), resulting in decreased conduction velocity and increased refractoriness. ### Class IA Agents Quinidine, Procainamide, and Disopyramide are the three classic Class IA drugs. They share: - Moderate sodium channel blockade (intermediate Kon/Koff) - Potassium channel blockade - QRS widening on ECG - QT prolongation - Negative inotropic effects ### Comparison with Other Classes | Feature | Class IA | Class IB | Class IC | Class II | Class III | Class IV | |---------|----------|----------|----------|----------|-----------|----------| | **Na⁺ Channel Block** | Moderate | Weak | Strong | None | None | None | | **K⁺ Channel Block** | Yes | No | No | No | Yes | No | | **QRS** | Widened | Normal | Widened | Normal | Normal | Normal | | **QT** | Prolonged | Shortened | Prolonged | Normal | Prolonged | Normal | | **Example** | Quinidine | Lidocaine | Flecainide | Beta-blockers | Amiodarone | Verapamil | **High-Yield:** Quinidine is the prototype Class IA agent and is rarely used clinically due to proarrhythmic potential and GI side effects, but remains a frequent NEET PG question. **Clinical Pearl:** Class IA drugs carry significant risk of torsades de pointes due to QT prolongation, especially in hypokalemia or with concurrent QT-prolonging drugs. **Mnemonic:** **QRS + QT = Class IA** — both ECG intervals are prolonged, distinguishing Class IA from IB (QT short) and IC (QT normal).