Transmembrane potential changes and ventricular fibrillation during repetitive myocardial ischaemia in the dog.

Abstract

Electrophysiological changes occurring soon after experimental coronary occlusion were examined in 13 dogs by recording epicardial action potential, endocardial-epicardial conduction time and epicardial ST segment elevation during successive 5 min occlusions of the left anterior descending coronary artery. After initial coronary occlusion, action potential duration shortened from 182 .+-. 9 ms to 113 .+-. 9 ms at 2 min and conduction time was prolonged from 24 .+-. 1 ms to 71 .+-. 17 ms associated with progressive ST segment elevation. These changes were followed by potentials of slow response type morphology, alternans of action potential duration and amplitude, alternans of epicardial and endocardial ST segment elevation, and intermittent conduction block. Ventricular fibrillation was preceded by action potential alternans in 95% and by conduction block in 65% of instances and occurred at a time of maximum conduction delay. The concept of re-entry in the pathogenesis of early ventricular fibrillation is supported. Changes in action potential duration and conduction time were significantly greater during the 1st occlusion compared to subsequent occlusion periods. There was no significant difference between data taken from occlusions 2, 3, 4 or 5. The validity of experimental studies of myocardial ischemia based on comparisons of sequential coronary occlusions using the 1st as the control is questioned.