Perioperative myocardial infarction during cardiac surgery. Diagnosis, ECG and enzyme testing.

The detection of perioperative myocardial infarction is complicated by the variety of electrocardiographic changes normally seen concomitantly with cardiac surgery. Unequivocal electrocardiographic diagnoses based on new Q wave development and evolution of ST and T segments are virtually always confirmed by inappropriately high postoperative enzyme test results. For those patients exhibiting nondiagnostic but suggestive electrocardiographic changes, enzyme testing provides a valuable adjunct in determining whether infarction has indeed taken place. Enzyme testing, similarly, in and of itself, cannot provide the dichotomous situation between those patients experiencing infarction and those who are not. SGOT and LDH appear the most reliable indicators of infarction. CPK is quite volatile with sporadic occurrences of high enzyme elevations without obvious clinical or electrocardiographic explanation. The Ck isoenzymes provide a highly specific test for myocardial damage. However, their sensitivity is sufficiently great that a relatively minor cardiac manipulation may result in uninterpretable results.