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)
๐ The VaughanโWilliams Classification is a traditional system used to categorise anti-arrhythmic drugs based on their predominant mechanism of action on cardiac ion channels or receptors.
โก While imperfect (since many drugs have multiple actions), it remains a helpful framework for learning and clinical reference.
| Class |
Action |
Examples |
| Class Ia |
โฌ๏ธ Prolongs action potential duration (moderate Naโบ channel block, some Kโบ block) |
Disopyramide, Procainamide, Quinidine |
| Class Ib |
โฌ๏ธ Shortens action potential duration (weak Naโบ block, fast kinetics) |
Lidocaine, Mexiletine, Tocainide |
| Class Ic |
Minimal effect on action potential duration, but marked Naโบ channel block |
Flecainide, Propafenone |
| Class II |
ฮฒ-blockade: โฌ๏ธ sympathetic activity, slows AV node conduction |
Metoprolol, Atenolol, Bisoprolol, Propranolol |
| Class III |
โฌ๏ธ Prolong repolarisation (Kโบ channel block โ prolongs QT) |
Sotalol, Amiodarone, Dofetilide, Ibutilide |
| Class IV |
Caยฒโบ channel blockade: slows AV node conduction |
Verapamil, Diltiazem |
๐ก Key Notes
- โ ๏ธ Class Ia & Class III drugs can prolong QT interval โ risk of torsades de pointes, especially with hypokalaemia or hypomagnesaemia.
- ๐งช Class Ib drugs (e.g., lidocaine) are particularly useful in ischaemia-induced ventricular arrhythmias.
- ๐ซ Class Ic agents (flecainide) are powerful but contraindicated in structural heart disease due to pro-arrhythmic risk.
- ๐ Class II and IV drugs mainly act on the AV node โ useful in rate control of atrial fibrillation/flutter.
- ๐ Many modern agents (e.g., amiodarone) act on multiple classes โ VaughanโWilliams is a simplification.
โ
Clinical Pearl:
Remember โSome Block Potassium Channelsโ โ
Sodium channel blockers (Ia, Ib, Ic),
Beta-blockers (II),
Potassium channel blockers (III),
Calcium channel blockers (IV).
