Classification of antiarrhythmic drugs

Vaughan-Williams classification

Class Mechanism Drugs
Ia Sodium blockade – prolongs refractory period of cardiac muscle Quinidine, Procainamide
Ib Sodium blockade – shortens refractory period Lidocaine, Phenytoin
Ic Sodium blockade – no effect of refractory period Flecainide
II Beta blockade – prolongs phase 4 Propranolol, Atenolol
III Potassium channel blockade – slows rate of repolarisation and prolongs action potential Amiodarone, Sotalol
IV Calcium channel blockade (L-type) – prevents maintenance of action potential Verapamil, Dilatiazem

Class I
Sodium blockade, therefore membrane stabilisers.

Class II
Block the effect of catecholamines at the Beta-1 adrenergic receptor, decreasing sympathetic activity on the heart. Decrease conduction through the AV node.

Class III
Potassium channel blockers, therefore prolong repolarisation and action potential duration

Class IV
Decrease conduction through the AV node
Shorten phase II (plateau phase)
Reduce contractility
Adrenergic control of heart rate maintained

An alternative classification

Digoxin, adenosine and magnesium do not fit into the Vaughan-Williams classification.

Drugs that work on
Supraventricular tachycardias Class Ic – Flecainide
Class II – Beta blockers
Class IV – Ca channel blockers
Digoxin
Adenosine
Ventricular tachycardias Class Ia – Procainamide
Class Ib – Lidocaine and Phenytoin
Both Class III – Amiodarone

Review: Myocyte action potential, Pacemaker action potential.

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