Activation of the Ischemic Ventricle and Acute Peri-Infarction Block in Experimental Coronary Occlusion

Changes in left ventricular activation during the first 10 min. following occlusion of the anterior descending branch of the left coronary artery of dogs were studied by using multiple intramural electrodes. Intramural block and an increase in the amplitude of R were observed routinely in the outermost layers of muscle in the central zone of maxi-mal ischemia as long as the occlusion was maintained. The changes were distinct from those produced by left bundle-branch block. Failure to propagate the accession process in normal fashion seems to be characteristic of ischemic heart muscle. D URING the course of a series of experi-ments to stud\ ' the acute changes produced by coronary occlusion on the re-covery process of the electrocardiogram of the dog, an increased amplitude of E and a delayed intrinsic deflection were observed. These changes have not been studied in de-tail, though reported previously.1 In order to evaluate the significance of these changes experiments were designed to examine (1) the supposition that a form of intraventricu-lar block distinguishable from left bundle-branch block is produced by coronary artery occlusion, (2) the reason for an increased amplitude of R in the ischemic region, (3) the incidence of local ventricular block asso-ciated with occlusion, (4) the duration, ex-tent, and disappearance of block when the occlusion is released, and (5) the general order of activation of the left ventricle during the first few minutes of experimental coro-nary artery occlusion. METHODS Experiments were conducted on healthy mon-grel dogs anesthetized with intravenous injection of pentobarbital sodium, the initial dose being 2/