Antiarrhythmics: Vaughan Williams Classification

Key points

• Class I (membrane-stabilising, block Na⁺ channels): Ia prolongs action potential (quinidine, procainamide, disopyramide) · Ib shortens it (lidocaine, mexiletine, phenytoin) · Ic no effect (flecainide, propafenone).
• Class II: beta-blockers (e.g. propranolol, atenolol) — anti-sympathetic.
• Class III: block K⁺ channels → prolong action potential/refractory period (amiodarone, sotalol).
• Class IV: calcium channel blockers (verapamil, diltiazem).
• Vaughan Williams is based on mechanism of action; amiodarone actually has class I–IV activity.