13.01.6 Class IV

Class IV anti-arrhythmic agents are Ca²⁺ channel blockers. Verapamil preferentially blocks cardiac Ca²⁺ channels over vascular Ca²⁺ channels. Thus, verapamil inhibits the inward Ca²⁺ current associated with pacemaking. Verapamil also slows conduction through the atrio-ventricular node. Verapamil is used in arrhythmias associated with increased excitation of sino-atrio or atrio-ventricular node. Verapamil is active after oral administration but does undergo extensive first pass liver metabolism. Verapamil can also be used intravenously in an emergency.