Antiarrhythmic Drugs

Antiarrhythmics are classified traditionally according to the Vaughn–Williams system (see Table 25.1). This system is not particularly useful as many drugs are not included (e.g. adenosine and digoxin) and many could fit into more than one category (e.g. amiodarone and sotalol). However, the examiners still expect you to know it. Many of the drugs have actions other than just their antiarrhythmic ones, and they are discussed in more detail in their relevant spider diagrams. Table 25.1 Vaughn-Williams classification of antiarrhythmics

Class

Mechanism

Drug

Ia

Blocks fast Na⁺ channels in cardiac myocytes.

Quinidine, procainamide, disopyramide

↑ Refractory period

Ib

Blocks fast Na⁺ channels in cardiac myocytes.

Lignocaine, phenytoin, mexiletine

↓ Refractory period

Ic

Blocks fast Na⁺ channels in cardiac myocytes.

Flecainide, propafenone

No effect on refractory period

II

β-adrenoreceptor blockade

Atenolol, propranolol, esmolol

III

K⁺ channel blockade

Amiodarone, sotalol, bretylium

IV

Ca²⁺ channel blockade

Verapamil, diltiazem