Perioperative Myocardial Ischemia

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Abstract
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 ischemic pattern in the development of intra- and postoperative myocaridal ischemia and infarction. Accordingly, the authors compared the frequency and severity of pre-, intra-, and postoperative ischemic episodes (ST-segment depression .gtoreq. 0.1 mV or elevation .gtoreq. 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 within acute change (.+-.20% of control) in blood pressure or heart rate. Intraoperative myocardial ischemia occurred in 33% of those patients with preoperative 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) occurred in seven patients. Although all seven major outcomes were preceded by ischemic episodes at some time during the study, perioperative ischemia was not a specific predictor of major outcome. The authors conclude that: 1) CABG patients have frequent preoperative episodes of myocardial ischemia, most of which are silent; 2) anesthesia and surgery do not worsen the preoperative ischemic pattern; 3) ECG changes suggestive of myocardial ischemia frequently follow CABG surgery, although their pathogenesis and significance is as yet unknown; 4) the majority of perioperative ischemic ECG changes occur within acute hemodynamic changes prior to the onset of ischemia; and 5) because the preoperative ischemic pattern appears to be recapitulated intraoperatively, it is relevant to examine the preoperative ischemic pattern to assess the impact of anesthesia and surgery in the development of intraoperative myocardial ischemia.