Complications of coronary bypass surgery

Use of survival analysis to determine the clinical significance of new Q waves after coronary bypass surgery

There are few data on the long-term effects of new Q waves on survival and morbidity after coronary bypass graft surgery (CABG). We followed 1340 patients who underwent CABG in 1978 at 10 hospitals participating in the Coronary Artery Surgery Study (CASS). The incidence of perioperative Q-wave infarction was 4.76% (range 0.0-10.3% by hospital). The rate of infarction was higher in patients who had an increased left ventricular end-diastolic pressure or cardiomegaly on the preoperative chest radiograph. Patients who received more grafts or who had longer cardiopulmonary bypass time were also at higher risk of infarction. In a stepwise discriminant analysis of 44 clinical, angiographic and surgical variables, cardiopulmonary bypass time, topical cardiac hypothermia and cardiomegaly entered the stepwise selection of variables. Long-term survival was adversely affected by the appearance of new postoperative Q waves. The hospital mortality was 9.7% in the 62 patients who had new postoperative Q waves and 1.0% in the 1278 patients who did not (p less than 0.001); the 3-year cumulative survival rates were 85% and 95%, respectively (p less than 0.001). In patients who survived to hospital discharge, the presence of new postoperative Q waves did not adversely affect 3-year survival (94% and 96%, respectively). The survival rates were worse in patients who had a history of infarction or who had impaired left ventricular function preoperatively. The number of readmissions to hospital after CABG among the patients who had a transmural perioperative infarction was similar to to that among patients who did not. We conclude that the appearance of new Q waves after CABG adversely affects survival. The major impact on mortality occurs before hospital discharge. Patients who are destined to have a perioperative infarct cannot be predicted from commonly measured preoperative and angiographic variables.

Diagnostic criteria for acute myocardial infarction in patients undergoing coronary artery bypass surgery

Current techniques for diagnosing perioperative myocardial infarction were studied in 58 patients who underwent coronary bypass surgery. All patients had preoperative and postoperative ECGs and technetium-99m stannous pyrophosphate myocardial scintigrams; serum CK-MB was measured immediately after surgery and daily for 3 days. Postoperative bypass graft visualization and left ventriculography were performed before hospital discharge in every patient. Nine patients (16%) had new Q waves postoperatively. Five of these nine patients had positive pyrophosphate scintigrams, postive CK-MB and new wall motion abnormalities, and the remaining four had negative CK-MB, negative phyrophosphate scintigrams and no new wall motion abnormalities. Seven patients (12%) had newly positive postoperative pyrophosphate scintigrams, positive CK-MB and new wall motion abnormalities on postoperative ventriculography, but only four had new Q waves postoperatively. Eight patients (14%) had new wall motion abnormalities; seven had positive pyrophosphate scintigrams and all had positive CK-MB, but only five had new Q waves. Sixteen patients (28%) had positive CK-MB, including all patients with either positive pyrophosphate scintigrams or new wall motion abnormalities, Eight patients had positive CK-MB without other evidence of perioperative infarction. A newly positive postoperative pyrophosphate scintigram is more senstive and specific than the development of new postoperative Q waves for the diagnosis of hemodynamically significatn perioperative myocardial in farction. CK-MB is highly sensitive, but too nonspecific to be useful for the diagnosis of perioperative infarction.

Detection of perioperative myocardial damage after coronary artery bypass graft surgery

In order to evaluate methods for detecting peri-operative myocardial damage we studied 41 patients before and serially following coronary artery bypass graft surgery utilizing the 12-lead ECG, serum MB-CPK measurements, and 99mTc pyrophosphate myocardial scans. Six of the 41 patients (15%) developed persistent new Q waves after surgery. Six other patients demonstrated ischemic ST-T wave changes that persisted for 48 hours or more. Mean total MB-CPK released was highest for the group with new Q waves [1598+/-545 (SE) I.U./L-hr] as compared to the group with ischemic ST-T wave changes 708+/-65 I.U./L-hr) or the group with no ECG changes (262+/-47 I.U./L-hr). Ten patients (24%) has positive postoperative pyrophosphate scans consistent with myocardial infarction. The three techniques were compared in these 41 patients utilizing 465 I.U./L.-hr as the upper limit of normal MB-CPK released after uncomplicated coronary bypass surgery (no ECG changes, negative scan). Five patients with ischemic ECG changes had a positive scan and high MB-CPK; six patients with no ECG changes had high MB-CPK but a negative scan; and one patient with high MB-CPK and new Q wave had a negative scan. We conclude 1) new Q waves on ECG underestimate the incidence of myocardial damage after coronary artery surgery; 2) MB-CPK alone overestimates the incidence of infarction; and 3) a combination of the three techniques is the best means for detecting myocardial damage after coronary artery bypass graft surgery.