1970 Volume 34 Issue 10 Pages 971-980
The mechanism of deviations of the ST segment of electrocardiogram has been explained by the hypothesis advocated by WILSON. While, since the introduction of the intracellular microelectrode method, it has been also investigated in the light of the membrane potential, the precise mechanism has not been clarified yet. Moreover, the mechanism of T wave changes is thought very complicated and is poorly understood. The present study was designed to observe a change in the membrane potential as well as a change of the ST-T in the unipolar surface elec-trogram during myocardial ischemia which was experimentally induced in the in situ heart of a dog by constricting or occluding the stem of the anterior descending branch of the left coronary artery for a limited time of 15 to 40 minutes. Furthermore, a correlation between a change in the membrane potential and a change of the ST-T in the unipolar surface electrogram was studied, and some discussions will be presented on the mechanism of the ST-T changes of electrocardiogram during myocardial ischemia from the standpoint of the membrane potential. Method Sixty adult dogs weighing 10 to 15kg were used in this experiment. A flow probe for an electromagnetic flowmeter was implanted in the course of the stem of the anterior descending branch of the left coronary artery, which was, then constricted or occluded at the point just proxiaml to the probe. On the epicardial surface of the central portion of the area receiving blood supply from the anterior descending branch, a steel-made double-ring consisting of an outer ring with the diameter of 2cm and an inner ring of 1cm was anchored by one or two stitches placed between the outer ring and the subepicardial muscular layer. Thus the movement of the myocardium encircled with the inner ring was markedly diminished. The epicardial surface within the inner ring served as a recording place of the unipolar surface electrogram and the membrane potential. Blood flow in the anterior descending stem, the unipolar surface electrogram and the membrane potential were simultaneously recorded and measured at intervals of 1 minute.
