Rate-dependent anisotropic conduction property in the epicardial border zone of canine myocardial infarcts and its modification by moricizine

Summary We evaluated anisotropic conduction properties, different conduction velocities depending on fiber orientation, in normal and infarcted myocardium and the effects of moricizine on anisotropic conduction. Various cycle lengths of stimulation were applied to 15 mongrel dogs, and epicardial mapping was performed using a 96-channel mapping electrode. Moricizine was then administered to seven dogs and the same procedure was performed. Conduction velocities were calculated from these maps. Programmed electrical stimulations were performed before and after moricizine administration to induce ventricular arrhythmias. Before moricizine administration, a rate-dependent decrease in longitudinal conduction velocity was observed in the infarcted zone. Moricizine suppressed longitudinal conduction in the normal zone significantly at 300 msec pacing, but not at slower rates. Moricizine at a dose of 4 mg/kg, on the other hand, suppressed longitudinal conduction in the infarcted zone significantly at all pacing cycle lengths. The effect of moricizine on transverse conduction was inconsistent. In three dogs, sustained ventricular tachycardia (VT) was induced either before or after moricizine administration. The mean cycle length of sustained VT was prolonged from 202 msec to 291 msec after 4 mg/kg of moricizine. Thus, the changes in cycle length of ventricular tachycardia observed were most likely the result of slowing of conduction velocity, especially in the longitudinal direction, in the infarcted myocardium. We conclude that the electrophysiologic nature of the subacute ischemic model was modified by moricizine, leading to depression of the conduction velocity of longitudinal conduction and the inducibility of ventircular arrhythmias.