Myocardial ischemia during cardiovascular surgery as detected by an ST segment trend monitoring system.

The incidence of intraoperative myocardial ischemia was determined in 312 patients undergoing cardiovascular surgery using ECG recordings obtained from a prototype system that trends ST segment changes. Prior to cardiopulmonary bypass, ischemic ECG changes were observed in 11.9% of patients, the incidence being lower during coronary artery bypass grafting (CABG) procedures (8.1%) than in patients undergoing repeated CABG (23.5%), valve replacement (25.9%), or concomitant valve replacement and CABG (35.3%). The occurrence of intraoperative myocardial ischemia was statistically greater in patients with a history of hypertension, two or more previous myocardial infarctions, or kidney disease. The incidence of ischemia was also significantly greater in patients with left ventricular end-diastolic pressures of 15 mm Hg or higher at cardiac catheterization. The incidence during induction was significantly reduced by the addition of hypnotics to narcotics, and, during maintenance, by the addition of an inhalational agent. The majority of ischemic events were temporally related to some hemodynamic disturbance, and many coincided with surgical manipulation. The incidence of intraoperative myocardial ischemia was substantially less than that reported in comparable studies. Since the incidence decreased significantly following clinical acceptance of the prototype system, the authors conclude that such capability increases sensitivity to small ST segment changes. This heightened awareness and prompt remedial action reduced the incidence of ischemia during CABG to 6% during the final 2 years of the study.