Does Perioperative Myocardial Ischemia Lead to Postoperative Myocardial Infarction?

Abstract

To determine if a relationship exists between perioperative myocaridal ischemia (ST segment depression .gtoreq. 0.1 mV) and post-operative myocardial infarction (PMI), nonparticipating observers recorded all ECG, hemodynamic, and other events between arrival of patients in the operating room and onset of cardiopulmonary bypass during 1023 elective coronary artery bypass operations (CABG). The roles of preoperative patient characteristics, quality of the operation limited by disease as rated by the surgeon and duration of ischemic cardiac arrest as risk factors for PMI also were quantified. ECG ischemia occurred in 36.9% of all patients, with almost half the episodes occurring before induction of anesthesia. PMI was almost 3 times as frequent in patients with ischemia (6.9% vs. 2.5%) and was independent of when ischemia occurred. Ischemia was related significantly to tachycardia but not hypertension or hypotension and was frequent in the absence of any hemodynamic abnormalities. The anesthesiologist whose patients had the highest rates of tachycardia and ischemia had the highest rate of PMI. Although neither single nor multiple preoperative patient characteristics related to PMI, suboptimal quality of operation and prolonged ischemic cardiac arrest increased the likelihood of PMI independent of the occurrence of myocardial ischemia. Perioprative myocardial ischemia is common in patients undergoing CABG, occurs randomly as well as in response to hemodynamic abnromalities, and is one of 3 independent risk factors identified as related to PMI. PMI is unrelated to preoperative patient characteristics such as ejection fraction and left main coronary artery disease, and its frequency will relate primarily to perioperative management rather than patient selection.