Comparison of cardiac troponin I versus T and creatine kinase MB after coronary artery bypass grafting in patients with and without perioperative myocardial infarction

Abstract

Background and purpose: Cardiac troponins have shown to be specific markers of myocardial injury. The aim of this prospective study was to compare patterns and kinetics of troponin I and T after coronary artery bypass grafting (CABG) with or without perioperative myocardial infarction (PMI).

Patients and methods: 119 patients (male/female: 96/23, age 64 +/- 10 years) underwent first time elective CABG. Preoperative mean ejection fraction was 55.8% +/- 15.6%. The mean number of grafts was 3.1 +/- 1.1/patient, in 85.7% the internal mammary artery was used. Cardiac troponin I (cTnI) and T (cTnT) levels, total serum activities of creatine kinase (CK) and creatine kinase isoenzyme MB (CK-MB) were measured before operation, at arrival on the intensive care unit (ICU), and 6, 12, 24, 48, and 120 h after unclamping of the aorta. Twelve lead electrocardiograms (ECGs) were recorded preoperatively and at days 1, 2, and 5. Perioperative data and postoperative cTnI and cTnT levels were correlated statistically.

Results: Two patients died due to refractory myocardial failure in the early postoperative period. For further evaluation, patients were divided in two groups according to postoperative ECG changes (group I: patients without PMI, n = 107; group II: patients with PMI, n = 10: six of them with Q-wave and four of them with non-Q-wave PMI). Calculated best cutoff values for cTnI and cTnT were 8.35 microg/l and 0.768 microg/l in ROC (receiver-operator characteristic) analysis. Serum concentrations of cTnI, and cTnT were in the normal range preoperatively and increased significantly after surgery in both groups. In both groups, cTnI reached its medium peak level after 24 h (group I: 2.7 microg/l, 95% confidence interval [CI]: [2.1,3.2]); group II: 70.5 microg/l). CTnT reached its medium peak level in group I without PMI after 48 h (0.298 microg/l, 95% CI: [0.254,0.354]), in group II with PMI not until 120 h (3.0 microg/l) postoperatively. In group II serum level of both troponins remained considerably high at 120 h (cTnI median = 10.75 microg/l, cTnT median = 3 microg/l).

Conclusion: Release patterns of cTnI and cTnT after CABG are different: cTnI reaches its postoperative peak value earlier and declines more quickly than cTnT. After uncomplicated CABG, serum levels of both cardiac troponins remain continuously low. Elevated concentrations reflect perioperative myocardial ischemia or infarction. CTnT shows a different release pattern in patients with or without myocardial infarction.