CHARACTERISTICS OF PATIENTS AT RISK FOR PERIOPERATIVE MYOCARDIAL-INFARCTION AFTER INFRAINGUINAL BYPASS-SURGERY - AN EXPLORATORY-STUDY

Patients requiring infrainguinal bypass surgery often have diffuse atherosclerotic disease, and perioperative myocardial infarction (MI) is a potentially lethal complication that is not uncommon in these patients. To establish additional clinical characteristics that might be useful in identifying patients who require more extensive cardiac evaluation, we conducted an exploratory case-control study comparing 22 patients who had a perioperative MI following elective infrainguinal bypass surgery with 191 control subjects whose bypasses were uneventful. In addition to previously recognized risk factors (e.g., history of angina or prior MI), we examined the association of perioperative MI with (1) results of common preoperative laboratory tests and ECG, (2) preoperative use of certain medications, and (3) intraoperative factors that might be anticipated prior to surgery (e.g., duration of surgery or type of anesthesia). Perioperative MI was associated not only with a history of angina, prior MI, or coronary artery disease but also with the need for certain cardiac medications, higher white blood cell (WBC) counts, ST-segment depression, left bundle branch block, and lengthy surgical procedures. Multiple logistic regression analysis identified the following factors as being independently associated with perioperative MI: preoperative antiarrhythmic agents (odds ratio [OR] = 26.4, p = 0.006), nitrates (OR = 8.4, p = 0.006), calcium channel blockers (OR = 5.5, p = 0.04), and aspirin (OR = 6.8, p < 0.01) and ST-segment depression (OR = 11.8, p = 0.01), WBC count (OR = 1.27/1000, p = 0.005), and duration of surgery (OR = 2.2/hr, p = 0.0001). In patients undergoing infrainguinal bypass surgery, perioperative MI is associated not only with a history of previous cardiac events and ECG evidence of ischemia but also with regular use of certain cardiac medications, higher WBC counts, and longer surgical procedures. Incorporation of these variables into current methods of risk assessment might improve their predictive value sufficiently to provide an objective, inexpensive means of distinguishing patients who warrant extensive preoperative cardiac evaluation from those who do not.