Indications for angiography subsequent to coronary artery bypass grafting

Background Postoperative myocardial infarction is a rare, but potentially severe complication after coronary artery bypass grafting (CABG). Early markers for coronary bypass graft failure or native vessel occlusion are required, because immediate intervention could prevent major myocardial damage. Methods One thousand patients with coronary artery disease consecutively underwent CABG. Postoperative coronary angiography was performed in 40 patients with suspected myocardial ischemia. Creatine kinase (CK), CK-MB, leukocyte count, C-reactive protein (CRP), lactate dehydrogenase (LDH), and glutamate-oxalacetate transaminase (GOT) were assessed at 0, 6, 12, 24, 48, and 72 hours after CABG as well as 12-lead standard electrocardiography (ECG). Results Postoperative angiography of 40 patients with suspected myocardial infarction revealed graft failure or occluded native vessels in 13 (32.5%) individuals. Patients with graft or vessel occlusion presented elevated (P < .005) leukocyte counts (17 215 ± 6632 vs 10 773 ± 3902 G/L) immediately after CABG. CK-MB concentrations differed (P < .05) at 6 hours after CABG (54 ± 48 vs 30 ± 18 U/L). CK, CRP, LDH, and GOT did not show any differences between both groups. Frequency of ECG ST-segment elevation was increased (P < .05) in ischemic patients (69.2% vs 29.6%). Conclusions Common signs of myocardial ischemia usually allow to diagnose unstable angina or myocardial infarction under native conditions. In contrast, these criteria frequently fail after CABG. Combined diagnostic criteria of elevated leukocytes (>14 000 G/L, at hour 0) and either ST elevation or CK-MB concentrations >35 U/L (at hour 6) at least seem to be very useful in detecting myocardial infarction after bypass grafting. In parallel, CK-MB elevation (>70 U/L, at hour 6) alone seems to predict ischemia. Both criteria should indicate angiography and potential revascularization. If these conditions were not fulfilled, the risk of perioperative myocardial infarction appears to be moderate.