Effect of Anoxemia upon Electrocardiogram of Cats after Coronary Ligation

Abstract

Ligation of the left branch of the left anterior descending coronary artery in cats results in typical “coronary” electrocardiographic records. These abnormal tracings frequently disappear in 2 to 3 weeks despite the persistence of grossly demonstrable infarcts at autopsy. Following the suggestion of Levy, Bruenn, and Russell 1 that the electrocardiographic changes which anoxemia induces in patients with coronary disease, may be of diagnostic value, these cats were subjected to mild anoxemia. When normal cats, anesthetized with pentobarbital, were made to breathe 10% oxygen in nitrogen for 20 minutes, the electrocardiographic changes induced were slight, and unlike those following coronary ligation.

Immediately after coronary ligation, the electrocardiograms of 7 of the 8 cats studied showed deviation of the RS-T segment in 19 of 21 leads. The electrocardiogram of the eighth cat was normal, but subsequently showed RS-T segment deviation. The T-waves were generally increased in amplitude. At this time, the induction of mild anoxemia exaggerated the RS-T deviations in 13 of the 19 leads, and elicited RS-T deviations in the electrocardiogram of the one cat in which they were lacking postoperatively. T-wave changes were slight and variable. The induction of the anoxemia was repeated at weekly intervals thereafter and continued to exaggerate the RS-T deviations, or to cause their reappearance.

Meanwhile, the RS-T segments of the electrocardiograms of the non-anoxemic cats approached the iso-electric line, and the electrocardiograms of 6 of the 8 cats returned to normal within from 12 to 29 days. One of the 2 cats whose electrocardiograms continued to show “coronary” changes was sacrificed 14 days postoperatively because of impending exitus from “snuffles.” The other continued to show electrocardiographic changes until it was sacrificed, 50 days postoperatively. When the electrocardiograms had returned to normal, the induction of anoxemia resulted in the reappearance of “coronary” complexes in every case.