13.01.6 Class IV

Class IV anti-arrhythmic agents are Ca2+ channel blockersVerapamil 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.