Importance of long-duration postoperative ST-segment depression in cardiac morbidity after vascular surgery

Major vascular surgery is associated with a high incidence of cardiac ischaemic complications. By means of continuous perioperative electrocardiographic recording, we studied 151 consecutive patients undergoing major vascular surgery to find out the characteristics of any myocardial ischaemia and the relation to outcome. 13 (8·6%) patients had postoperative cardiac events (6 myocardial infarctions, 2 unstable angina, and 5 congestive heart failure). There were 342 perioperative ischaemic episodes shown by ST-segment depression; 164 (48%) occurred postoperatively. Postoperative ischaemic episodes were significantly longer than episodes before or during operations (3·2 vs 1·7 and 1·5 min per h monitored, respectively, p<0·001). Both Detsky's cardiac risk index and long-duration (>2 h) preoperative ischaemia were predictive of postoperative cardiac complications (odds ratios in univariate analysis 3·3, p=0·03, and 7·2, p=0·009, respectively). However, long-duration (>2 h) postoperative ischaemia was the only factor significantly associated with cardiac morbidity in multivariate logistic regression analysis (odds ratio 21·7, p=0·001). Long-duration ST-segment depression preceded most (84·6%) postoperative cardiac events, including myocardial infarctions, and no cardiac event was preceded by ST-segment elevation. 5 of the 6 postoperative myocardial infarctions were non-Q-wave infarctions. We conclude that long-duration subendocardial ischaemia, rather than acute coronary artery occlusion, may bring about postoperative myocardial injury and complications.