Group I antiarrhythmics 

Group 1 antiarrhythmics: Sodium-channel blockers, which block the fast sodium channels, thereby slowing electrical conduction in the heart.

Sodium-channel blockers comprise the Class I antiarrhythmic compounds according to the Vaughan-Williams classification scheme. These drugs bind to and block fast sodium channels that are responsible for rapid depolarization (phase 0) of fast-response cardiac action potentials.