Characteristics of electrocardiographic ischemia in high-risk patients undergoing surgery. Study of Perioperative Ischemia (SPI) Research Group.

Perioperative cardiac morbidity remains a significant problem in both cardiac and noncardiac surgical patients. The role of perioperative myocardial ischemia appears to be important and is under active investigation. In a series of studies in 200 high-risk patients undergoing noncardiac surgery or coronary artery bypass graft (CABG) surgery, we measured the pre-, intra-, and post-operative electrocardiographic (ECG) ischemic patterns using either continuous 2-lead ambulatory (Holter) monitoring or continuous 12-lead (modified treadmill) monitoring. Electrocardiographic ischemic episodes were defined as reversible ST-segment changes lasting at least 1 min and involving a shift from baseline (adjusted for positional changes) of greater than or equal to 0.1 mV of ST depression (with slope less than or equal to 0) at J + 60 ms or 0.2 mV of ST elevation at the J-point. During the 2-day period preceding surgery, ECG ischemic changes were common, clinically silent, and usually independent of changes in myocardial oxygen demand. Intraoperatively, using continuous 12-lead ECG, we found a 25% incidence of ischemia, for which modified leads V5, V4, and II were the most sensitive. Most ECG ischemic episodes were supply-dependent, not demand-dependent. Comparing the pattern of intraoperative ischemia with the chronic ambulatory preoperative pattern, we found that, under conditions of strict hemodynamic control, intraoperative ischemia apparently recapitulated the preoperative pattern, and that the stresses of anesthesia and surgery contributed less than previously thought. The highest incidence of ischemia occurred postoperatively, ranging between 30% and 60%, in both cardiac and noncardiac surgical patients.(ABSTRACT TRUNCATED AT 250 WORDS)