Scintigraphic, electrocardiographic, and enzymatic diagnosis of perioperative myocardial infarction in patients undergoing myocardial revascularization

To assess the incidence of perioperative myocardial infarction, 214 consecutive patients were evaluated 1-5 days after coronary bypass surgery, using Tc-99m pyrophosphate (TcPPi) myocardial imaging, serial electrocardiograms (ECG), and enzyme levels (SGOT, LDH, CPK). On the basis of the clinical course and scintigraphic, enzymatic, and ECG changes, the diagnosis of perioperative infarction was definite in 17 of 214 cases (7.9%) and probable in 6 of 214 (2.8%). In all of these 23 patients, TcPPi scans were abnormal; 1 additional patient had a false-positive scintigram. Only 13 of the 23 had ECG evidence of infarction, but there were no false positives. The authors set the threshold for abnormality of enzyme changes quite high, owing to experience in more than 900 postoperative patients (SGOT > 200, LDH > 500, CPK > 500 on the same day). Using these criteria, 22 of the 23 infarct patients had abnormal enzymes, and 6 others were falsely positive. These results indicate a relatively low sensitivity for the ECG in diagnosing perioperative infarction, but the lack of false positives suggests high specificity. The sensitivity and specificity of the enzymes and the TcPPi image were both excellent and quite similar; the main difference was a reduction of certainty of infarction with the enzyme criteria, caused by the 6 patients whose enzyme values were falsely positive. Considering its sensitivity, specificity, and ability to locate and to a certain extent quantitate necrosis, TcPPi imaging is probably the most valuable means of diagnosing perioperative myocardial infarction.