Observations on Coronary Occlusion. ∗ II. Electrocardiographic Changes

Abstract

In the course of experiments designed to study the effects of coronary artery ligation in dogs 1 it has been interesting to observe rather varied electrocardiographic changes and at this time a brief note is presented to describe some of the characteristic features observed.

Seventeen dogs were used. Under amytal anesthesia, with respirations maintained by positive pressure, the pericardium was exposed by a subperiosteal resection of the anterior portion of the fourth rib on the left. The anterior descending branch of the left coronary artery was ligated 1.5 cm. from its origin. Using conventional limb leads, electrocardiographic tracings were taken at hourly intervals for the first 12 hours, again at 24 hours, at daily intervals for the next week, and at weekly intervals thereafter. In each instance a control tracing was taken before the operation was begun, the animal being under full amytal anesthesia at the time. Two dogs served as controls. The operative procedures were duplicated in every detail except the actual tying of the ligatures about the coronary artery.

The changes noted consisted of (A) disturbances of rhythm and (B) changes in direction and configuration of the T, ST and RST components of the electrocardiogram.

A. Disturbances of Rhythm. In 6 dogs ventricular fibrillation appeared as a terminal phenomenon within from 3 to 20 minutes following ligation. In a seventh dog ventricular fibrillation was noted approximately 23 hours after ligation. In this dog the ventricular fibrillation was transient, was followed successively by ectopic ventricular tachycardia, premature ventricular contractions, and finally by normal rhythm. Nodal and ventricular premature beats appeared in approximately half of the dogs at varying intervals after ligation—3 1/2 to 24 hours—with the greatest incidence of onset from 6 to 8 hours after ligation. Usually within an hour or 2 after the onset of premature contractions, an irregular, ectopic ventricular tachycardia set in. The appearance of ectopic ventricular tachycardia usually presaged death of the animal within 24 to 48 hours. In 2 instances, however, the animals survived, the rhythm later reverting to normal.