Alila Academy

Antiarrhythmic agents are drugs used to suppress abnormal rhythms of the heart. They act to either:

- interfere with the dynamics of cardiac action potentials by blocking a certain ion channel, 

or

- block the sympathetic effects of the autonomic nervous system on the heart, to slow down heart rate.

There are 5 classes of antiarrhythmic drugs:

• Class I: Sodium-channel blockers: these drugs bind to and block the fast sodium channels that are responsible for the depolarizing phase in contractile myocytes. The result is a slower depolarization with a smaller amplitude. Slower influx of sodium results in a smaller flow of positive ions through gap junctions to adjacent cells; the adjacent cells take longer to reach the threshold required to generate a new action potential, ultimately resulting in a slower propagation of action potentials through the myocardium. This reduced conduction velocity helps to suppress formation of re-entrant circuits, hence the use of these drugs for treating re-entrant tachycardias.

Class I agents are divided further into subclass IA, IB and IC. These subclasses differ in the strength of sodium channel blockage, and in their effect on the duration of action potentials and the effective refractory period (ERP).

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