Form of the Electrocardiogram in Experimental Myocardial Infarction

Abstract

In a series of experiments still incomplete we have attempted to determine how the changes in the initial and final deflections of the ventricular complex observed in standard and precordial 1 electrocardiograms in clinical coronary thrombosis are produced. In these experiments, performed upon fully anesthetized dogs, we have ligated the anterior descending branch of the left coronary artery or one of its major subdivisions, and have employed direct and semi-direct leads 1 as well as the usual standard leads in studying the alterations in the electrical phenomena associated with the heart beat that this procedure produces. The results of the experiments carried out thus far may be summarized as follows:

Almost immediately after the ligation of a coronary artery the electrical curves obtained by leading directly from the epicardial surface of the region supplied by it become essentially monophasic, and are similar to those obtained when the same portion of the heart's surface is injured by burning or by other means. The direction of the monophasic response is such as to indicate relative positivity of the electrode in contact with the heart (the exploring electrode) or relative negativity of the indifferent electrode, which is placed in contact with the subcutaneous tissues of the right or left hind leg. The displacement from the base line of the final portions of this monophasic curve, which correspond in time to the RS-T segment and T-deflection of the standard electrocardiogram, rapidly diminishes, but does not, apparently, completely disappear for several days.

Twenty-four to 48 hours after coronary ligation, the electrical responses obtained by leading directly from the infarcted region are quite different from those described in the preceding paragraph. They show no proper intrinsic deflection and no preliminary downward movement such as precedes that deflection in the curves obtained from other portions of the heart.