The relationship between ventricular arrhythmias and ischemia-induced conduction delay in closed-chest animals within 24 hours of myocardial infarction.

To investigate the myocardial conduction characteristics of premature impulses during the first 24 hours following coronary ligation and its relationship to late infarction ventricular arrhythmias, transmural electrodes were positioned in the normal and ischemic myocardium in nine dogs. Cardiac conduction in ischemic myocardium was delayed 15 minutes post coronary occlusion both in the epicardium and endocardium, both in the anterograde (base to apex) and retrograde (apex to base) direction, and was maintained at the same level throughout the experiment. Conduction across the border of ischemic myocardium from ischemic to the normal segment was also delayed, especially in the endocardium. Spontaneous ventricular arrhythmias recorded on Holter tapes showed significant increase in the number of premature ventricular complexes and ventricular tachyarrhythmias 9 hours after infarction. Thus our findings suggest that spontaneous arrhythmias occurring in the late phase of acute myocardial infarction (AMI) are independent of the ischemia-induced conduction delay and an alternate mechanism such as abnormal automaticity may be responsible for late ventricular arrhythmias.