Relationship of alternans of monophasic action potential and conduction delay inside the ischemic border zone to serious ventricular arrhythmia during acute myocardial ischemia in dogs

We studied the relationship of conduction delay and monophasic action potential (MAP) at an ischemic border zone to serious ventricular arrhythmia (VA). Measurements were made in 36 adult mongrel dogs 15 minutes after occlusion of the left anterior descending coronary artery. We recorded MAPs and bipolar electrograms simultaneously inside and outside the ischemic border zone in the dog hearts. Of the 36 dogs, 24 that had favorable MAP recordings were chosen and were divided into two groups according to an occurrence of VA. In group A (n = 12), an onset time of VA was 5.1 +/- 0.8 minutes after ischemia, while in group B (n = 12) VA did not occur during ischemia. The conduction delay at the ischemic border zone was significantly greater from 3 minutes after ischemia in group A than in group B. MAP alternans, defined as the difference in duration of two consecutive MAPs inside the ischemic border, was marked in group A but mild in group B. Duration of a small MAP of alternans was markedly shorter than that of a corresponding MAP outside the ischemic border in both groups, but was followed by VA in group A. Duration of a large MAP was markedly prolonged compared with that of a corresponding MAP outside the ischemic border in seven dogs of group A and in only one dog of group B (p less than 0.01), and was followed by VA in seven dogs of group A. Our results suggest that the mechanism of VA is due not only to reentry but also to an injury current flowing from ischemic to nonischemic tissues, because VA was preceded by conduction delay and by a difference in MAP durations when comparing regions inside and outside the ischemic border.