Study objectives: To compare cardiac troponin I (cTnI), cardiac troponin T (cTnT), and creatine kinase MB (CKMB mass) in patients with and without new Q wave on the ECG following coronary artery bypass graft (CABG) surgery.
Patients: After ethic committee's approval and informed consent, 82 patients, mean age 63±10 years, scheduled for CABG were included.
Interventions: Arterial blood samples were drawn during cardiopulmonary bypass, before, and 6, 12, 24, and 48 h after aortic cross-clamp release. cTnI, cTnT, and CKMB mass were measured. The appearance of new Q wave on the ECG performed preoperatively and 24 h postoperatively was used to assess myocardial lesion independently of biological markers.
Results: There were 69 patients without new Q wave on the ECG (group 1) and 13 with (group 2). In group 1, cTnI reached a peak of 2.1 µg/L (median, interquartile range [IQ]=2.4) at 12 h, cTnT increased progressively with a peak of 0.22 µg/L (IQ=0.2) at 48 h, and CKMB presented an earlier peak of 10 µg/L (IQ=6.2) at 6 h. Starting with the same median value, group 2 patients presented significantly higher peaks: cTnI: 17 µg/L (IQ=16) at 12 h; cTnT: 1.4 µg/L (IQ=2.3) at 12 h; and CKMB mass: 74 µg/L (IQ=61) at 6 h. Receiver operating characteristic (ROC) curves were constructed. The area under the curve was 0.90 for cTnI, 0.84 for CKMB, and 0.81 for cTnT (not significant). The best cutoff values to discriminate between group 1 and group 2 patients were determined with the ROC curves: cTnI=5 µg/L; CKMB mass=20 µg/L; cTnT=0.3 µg/L. Sensitivity, specificity, and positive and negative values for cTnI (5 µg/L) were 91%, 82%, 53%, and 98%, respectively.
Conclusions: There was little differences among cTnI, cTnT, and CKMB after CABG to diagnose myocardial damage as assessed by new Q wave on the ECG. There was a trend of cTnI to be a better discriminator than cTnT, but it did not reach statistical significance.