Antiarrhythmic drugs: mechanism of action and classification

Antiarrhythmic drugs: mechanism of action and classification

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Antiarrhythmic drugs may be used to terminate or prevent arrhythmias. With the exception of digoxin and adenosine, they have traditionally been classified as possessing one or more of the four classes of antiarrhythmic action originally described by Vaughan Williams:

class I drugs inhibit the fast sodium channel

class II drugs inhibit the effects of the sympathetic nervous system

class III drugs prolong the action potential

class IV drugs inhibit the slow inward calcium current.

Class I drugs are further divided into three subgroups depending on whether they increase (IA), decrease (IB), or have no effect on (IC), the action potential duration. Drugs frequently have more than one activity (eg sotalol is a beta blocker but also has class III actions). While this classification system remains under debate and oversimplifies reality, it is widely used clinically.