The objective of this study was to evaluate serum cardiac troponin T and I levels
in patients in whom electrocardiogram, myocardial scan, and serum CK-MB levels of
the MB isoenzyme of creatine kinase indicated perioperative myocardial infarction
(MI) after coronary artery bypass grafting (CABG).
We studied 590 patients who underwent CABG at the Montreal Heart Institute between
1992 and 1996. Postoperative cardiac troponin T levels (493 patients), troponin I
levels (97 patients), and activity of the MB isoenzyme of creatine kinase, electrocardiograms,
clinical data, and clinical events were recorded prospectively. The diagnosis of perioperative
PMI was defined by a new Q wave on the electrocardiogram, by serum levels of the MB
isoenzyme of creatine kinase higher than 100 IU/L within 48 hours after operation,
or both.
After CABG, 22 patients in whom troponin T levels (22/493, 4.5%) and 6 patients in
whom troponin I levels (6/97, 6.2%) were measured had sustained a perioperative MI
according to current diagnostic criteria. In these patients, troponin T levels higher
than 3.4 microg/L 48 hours after CABG best detected the presence of perioperative
MI, with an area under the receiver operating characteristic curve of 0.95, a sensitivity
of 90%, a specificity of 94%, a positive predictive value of 41%, a negative predictive
value of 99%, and a likelihood ratio of 15. Serum troponin I levels higher than 3.9
microg/L 24 hours after CABG confirmed the perioperative MI with an area under the
receiver operating curve of 0.86, a sensitivity of 80%, a specificity of 85%, a positive
predictive value of 24%, a negative predictive value of 99%, and a likelihood ratio
of 5.
Serum troponin T levels higher than 3.4 microg/L 48 hours after CABG correlated best
with the diagnosis of perioperative MI. Serum troponin T levels greater than 3.9 microg/L
24 hours after CABG also correlated with the diagnosis of perioperative MI, although
a larger experience is needed to confirm the validity of the chosen cutoff value.