Electrocardiographic effects of myocardial ischemia induced by atrial pacing in dogs with coronary stenosis. I. Repolarization changes with progressive left circumflex coronary. artery narrowing.

The electrocardiographic effects of tachycardia in normal dogs and in dogs with progressive coronary stenosis were studied. In five animals, left atrial electrodes were surgically implanted and body surface isopotential patterns were recorded from 84 torso electrodes; pacing at rates of up to 250 beats/min increased recorded voltages registered during the ST segment but did not alter the spatial distribution of these potentials. In 10 dogs, an ameroid constrictor was also implanted about the left circumflex coronary artery. One week after surgery, pacing to rates of 250 beats/min had no effect on ST segment isopotential patterns. However, 2 and 3 weeks postoperatively, when significant coronary constriction was anticipated, pacing-induced ST segment depression was recorded along the inferior anterior and posterior chest surfaces. Abnormal negative voltages were more intense at 3 than at 2 weeks, but the distribution of these abnormalities was unchanged. This pattern was consistent with the location of ischemic myocardium. Calculation of early (10 to 40 ms) ST segment slopes demonstrated that downsloping forms were recorded over most of the area with abnormal ST segment voltages, but that horizontal or upsloping depression occurred at the margins of the abnormal zones. The findings suggest that this canine model may be a useful analog to clinical exercise stress testing to aid in evaluating the significance of clinical electrocardiographic patterns.