Perioperative Myocardial Ischemia: Importance of the Preoperative Ischemic Pattern

Previous studies investigating the incidence of myocardial ischemia in patients undergoing coronary-artery bypass grafting (CABG) surgery have not considered the potential significance of the preoperative myocardial ischemia and infarction. Accordingly, the authors compared the frequency and severity of pre-, intra-, and postoperative ischemic episodes (ST-segment depression ≥ mV or elevation ≥ 0.2 mV) in 50 men with severe coronary artery disease scheduled for elective CABG. All subjects were monitored by continuous electrocardiography (ECG) (Holter monitor) for 2 preoperative days, intraoperatively, and 2 postoperative days (total monitoring time = 4,363 h). Routine anti-anginal medications were continued until the morning of surgery, and the anesthetic management of the patient was not controlled. During the preoperative period, 42% of the patients had ECG ischemic episodes, 87% of which were clinically silent. Only 18% developed intraoperative ischemia. Postoperatively, the incidence increased to 40%. The number of ischemic episodes/hour (epis/h) of monitoring among the three monitoring periods was similar (0.09 ± 0.12 epis/h preoperatively, 0.11 ± 0.20 epis/h intraoperatively, and 0.05 ± 0.08 epis/h postoperatively; P = NS). The median duration of ischemic episodes was similar pre- and intraoperatively (16 vs. 18.5 min, P = NS), but greater postoperatively (41 min, P < 0.05). Seventy-six per cent of the perioperative ECG ischemia occurred without acute change (±20% of control) in blood pressure of heart rate. Intraoperative myocardial ischemia occurred in 33% of those patients with preopearative ischemia, but in only 7% of patients without preoperative ischemia (P < 0.05). However, neither pre- nor intraoperative ischemia predicted the development of postoperative ischemia, Major outcome (myocardial infarction and/or death) occured in seven patients. Although all seven major outcomes were preceded by ischemic episodes at some time during the study, perioperatiye ischemia was not a specific predictor of major outcome. The authors conclude that1) CABG patients have frequent preoperative episodes of myocardial ischemia, most of which are silent; 2) anesthesia and surgery do not worsen the prcoperative ischemic pattern; 3) ECG changes suggestive of myocardial ischemia fequently follow CABG surgery, although their pathogenesis and significance is as yet unknown; 4) the majority of perioperative ischemic ECG changes occur without acute hemodynamic changes p