[Perioperative myocardial infarction and cardiac complications after noncardiac surgery in patients with prior myocardial infarction. III: Troponin T--a significant diagnostic alternative in perioperative myocardial infarction?].

UNLABELLED: Diagnosis of a perioperative myocardial infarction (PMI) on the basis of measurement of the creatine kinase MB fraction (CKMB) alone is not always easy. Surgical traumatisation of muscle fibres can lead to false-positive elevations. Newly introduced laboratory tests for cardiac troponins seem to facilitate the diagnosis of PMI. We measured serum values of cardiac troponin T in 139 patients described in detail in part I and compared them with common diagnostic tools for myocardial infarction.

METHODS: In all, 139 patients were enrolled (part I). Clotted serum samples were taken preoperatively and daily until day 3, centrifuged, and stored at -20 degrees C until analysis. Our Department of Clinical Biochemistry and Haematology used a commercially available sandwich immunoassay (Troponin T ELISA, Boehringer, Mannheim, Germany). The measurements of CK and CKMB were performed with an automated analyser (CK, CK-MB, Boehringer, Mannheim, Germany). Serum values of troponin T were defined according to company recommendations: detection level: 0.04 ng/ml, threshold value for myocardial ischaemia: > or = 0.2 ng/ml, value for diagnosis of non-Q-wave infarction: > or = 1.0 ng/ml, and value for diagnosis of Q-wave infarction: > or = 3.0 ng/ml. We therefore assumed a value of > or = 1.0 ng/ml troponin T as being positive for MI, comparable with a CKMB value > or = 6% of total CK (part I). Statistical analysis was the same as described in part I.

RESULTS: Six of the 139 patients had a perioperative infarction, 3 of them had CKMB levels > or = 6%, 3 had an elevation of troponin T > or = 1.0 ng/ml. The sensitivity was 50% for both troponin T and CKMB. Values for specificity were 98% for troponin T and 95% for CKMB. Two of 8 patients with troponin T levels > or = 0.2 ng/ml preoperatively had a reinfarction (Table 5). Three of 8 patients with preoperative elevations of cardiac troponin T > or = 0.2 ng/ml versus 4 of 131 others had left ventricular failure postoperatively (P < 0.05). On day 3 significantly more patients with pathological levels of troponin T had left ventricular failure (5 of 12 vs. 0 of 127, P < 0.05). Patients with pathological depression of the ST segment on Holter ECG more often had elevations of troponin T values on day 3 than patients without (3 of 25 vs. 4 of 75, P = 0.048). There was an unexplained coincidence of elevated preoperative serum creatinine levels > 120 mumol/l and troponin T values (Table 6).

CONCLUSION: Troponin T is a highly specific marker for perioperative myocardial cell necrosis. Patients with raised levels preoperatively seem to be at higher risk for postoperative reinfarction and left ventricular failure. The prognostic value of such an elevation is not clearly defined, especially in patients with chronic renal failure.