Antiarrhythmic drugs treat dysrhythmias by restoring normal cardiac function. They are categorized based on their electrophysiological effects.

Class I antiarrhythmic drugs block open or inactivated voltage-sensitive Na⁺ channels in continuously depolarizing tissues. By reducing Na⁺ ion influx, they prevent auto-excitation and hinder action potential propagation.

Class I agents are subdivided based on their effects on the action potential duration and dissociation kinetics from the Na⁺ channel.

Class IA drugs feature intermediate dissociation kinetics and slow phase 0 depolarization. Additionally, they block K⁺ channels, prolonging the refractory period and action potential duration.

Class IB drugs exhibit fast dissociation kinetics. They do not affect phase 0 depolarization but shorten phase 3 depolarization and the action potential duration.

Class IC drugs possess slow dissociation kinetics, reducing phase 0 depolarization without affecting the action potential duration.

All class I drugs are proarrhythmic and show potential side effects like delayed conduction, tachycardia, and negative inotropy.