Reversibility of electrophysiologic abnormalities of subendocardial Purkinje fibers induced by ischemia.

Abstract

During the subacute phase of infarction in the canine heart, the subendocardial Purkinje fibers subtended by the infarct show depolarization greater than can be accounted for by the decrease in [K+]i, and generate abnormal action potentials and spontaneous rhythms due to abnormal automaticity. We have used pinacidil to hyperpolarize these fibers and evaluate the extent to which an increase in resting potential can normalize action potential generation. Twenty-four hours after two-stage ligation of the canine left anterior descending coronary artery, preparations of subendocardial Purkinje fibers were studied in vitro by recording transmembrane potentials through standard microelectrodes and exposing the preparation to pinacidil and increases in [K+]o. Pinacidil increased resting potential to the estimated value of EK, abolished the abnormal automaticity, and restored action potentials of normal amplitude with normal values of Vmax. This effect often persisted after washout of pinacidil. Elevation of [K+]o from 4.0 to 20.0 mM slightly increased maximum diastolic potential, suggesting that the excess (over the change in EK) depolarization was caused by a decrease in gK1. The ventricular arrhythmias seen during the subacute stage of infarction probably are caused by abnormal automaticity. Our findings support the conclusion that this abnormal automaticity arises in partially depolarized subendocardial Purkinje fibers. This loss of resting potential is due in large part to a decrease in gK1. Restoration of resting potential to the value of EK permits the Purkinje fibers to develop essentially normal action potentials. An agent capable of reversing the partial block of IK,1 thus might be an effective drug for some types of arrhythmias.