Myocardial Infarction as a Complication of Coronary Bypass Surgery

Serial postoperative ECGs were reviewed for all patients undergoing saphenous vein-coronary artery bypass graft (CABG) during 1969-71. Only the development of new pathologic Q waves were accepted as indicative of definite acute myocardial infarction (AMI). ST-T changes regardless of characteristics were not accepted as evidence of AMI. Operative mortality was 11% (27/253) with 59% (10/17) of those autopsied having AMI. Autopsy findings showed no false positives by ECG. Of survivors, 15% (33/220) had AMI. Another 2% (five) developed leftbundle conduction abnormalities and were considered probable for AMI. Among all patients having CABG, 20% (49/243) had AMI by ECG or autopsy. Comparing patients with and without AMI, there was no significant difference in coronary risk factors, hemodynamic data, number of vessels diseased, or site(s) of grafts. There was a significant difference in preoperative functional class for angina in the two groups. Seventy-six percent of those in the MI group had New York Heart Association class IV chest pain, whereas only 52.6% of the group without MI were class IV ( P < 0.05). In those with triple grafts (14 patients), five had AMI (36%) compared to 14% (20/143) with one or two grafts ( P < 0.02). Of patients with a pump time greater than 120 min, 29% (8/28) had AMI compared to 11% (16/146) with shorter pump times ( P < 0.02). A significantly larger number of the MI group developed class IV congestive heart failure postoperatively than the group without MI (13 vs 2%, P < 0.02). Despite the use of stringent criteria, this study shows that AMI complicating CABG is a common event. Those developing AMI at surgery had more severe chest pain preoperatively, had prolonged pump times, and a significantly larger number received triple grafts. Postoperatively, there was a higher incidence of severe congestive heart failure in those having an infarct at surgery.