The effects of amiodarone on repolarization and refractoriness of cardiac fibers

Abstract

The effects of superfusion (acute) and chronic amiodarone pretreatment on repolarization in dog Purkinje and guinea pig papillary muscle fibers were studied using standard microelectrode techniques. In dog Purkinje fibers superfusion with 5 and 50 micrograms/ml amiodarone shortened action potential duration, slowed restitution of premature action duration, and decreased the range of premature action potential durations. In Purkinje fibers from pretreated dogs action potential duration and range of premature action potential durations did not differ significantly from the corresponding control values but restitution was slowed. In guinea pig papillary muscle superfusion with 20 micrograms/ml amiodarone did not change action potential duration and restitution kinetics but in the muscle fibers from pretreated animals both the action potential duration and the range of premature action potential durations were increased. We concluded that the designation of 'class III action' applied to chronic amiodarone treatment in ventricular but not to chronic treatment in Purkinje fibers, and not to acute treatment in either fibers.