Related Subjects:
|Classical Ventricular Tachycardia
|Idiopathic Ventricular Tachycardia
|Ventricular Fibrillation
|Resuscitation - Adult Tachycardia Algorithm
|Resuscitation - Advanced Life Support
|Atrial Flutter
|Atrial Fibrillation
|Pacemakers
|Wolff-Parkinson White syndrome (WPW)
|Supraventricular Tachycardia (SVT)
📖 The Vaughan–Williams Classification is a traditional system used to categorise anti-arrhythmic drugs based on their predominant mechanism of action on cardiac ion channels or receptors.
⚡ While imperfect (since many drugs have multiple actions), it remains a helpful framework for learning and clinical reference.
| Class |
Action |
Examples |
| Class Ia |
⬆️ Prolongs action potential duration (moderate Na⁺ channel block, some K⁺ block) |
Disopyramide, Procainamide, Quinidine |
| Class Ib |
⬇️ Shortens action potential duration (weak Na⁺ block, fast kinetics) |
Lidocaine, Mexiletine, Tocainide |
| Class Ic |
Minimal effect on action potential duration, but marked Na⁺ channel block |
Flecainide, Propafenone |
| Class II |
β-blockade: ⬇️ sympathetic activity, slows AV node conduction |
Metoprolol, Atenolol, Bisoprolol, Propranolol |
| Class III |
⬆️ Prolong repolarisation (K⁺ channel block → prolongs QT) |
Sotalol, Amiodarone, Dofetilide, Ibutilide |
| Class IV |
Ca²⁺ channel blockade: slows AV node conduction |
Verapamil, Diltiazem |
💡 Key Notes
- ⚠️ Class Ia & Class III drugs can prolong QT interval → risk of torsades de pointes, especially with hypokalaemia or hypomagnesaemia.
- 🧪 Class Ib drugs (e.g., lidocaine) are particularly useful in ischaemia-induced ventricular arrhythmias.
- 🫀 Class Ic agents (flecainide) are powerful but contraindicated in structural heart disease due to pro-arrhythmic risk.
- 📊 Class II and IV drugs mainly act on the AV node → useful in rate control of atrial fibrillation/flutter.
- 🌍 Many modern agents (e.g., amiodarone) act on multiple classes → Vaughan–Williams is a simplification.
✅ Clinical Pearl:
Remember “Some Block Potassium Channels” →
Sodium channel blockers (Ia, Ib, Ic),
Beta-blockers (II),
Potassium channel blockers (III),
Calcium channel blockers (IV).
