Effects of lidocaine on the electrophysiological properties of subendocardial Purkinje fibers surviving acute myocardial infarction

Abstract An electrophysiologic study was conducted in vitro on the surviving subendocardial Purkinje fibers of the canine left ventricle 20 to 24 h after coronary occlusion. The surviving Purkinje cells displayed a low maximum diastolic potential, reduced action potential amplitude, depressed maximal rate of upstroke and a prolonged action potential duration. Spontaneous discharges of high frequency and induced repetitive activity are consistently observed in the infarcted zone but are rarely seen in the normal tissue. Superfusion of lidocaine hydrochloride in concentrations of 1 × 10 −5 to 1 × 10 −4 m slowed or abolished spontaneous and induced firings. The effective refractory period and effective refractory period relative to the total action potential duration were consistently prolonged by lidocaine in the ischemic fibers. Membrane response curves of ischemic fibers were shifted farther to the right than those of normal fibers. Lidocaine exhibited a differential effect on maximul rate of upstroke ( dV d t ) of ischemic Purkinje fibers while causing minor change in the normal fibers. It is suggested that lidocaine exerts its antiarrhythmic effect by selectively depressing the already depressed conducting fibers in the infarcted heart.