Serum isoforms of creatine kinase MM isoenzyme in acute myocardial infarction

Using the electrophoretic method, the changes in the catalytic activities of three CK-MM isoforms in multiple sequential serum samples of 12 patients with acute myocardial infarction (AMI) were monitored for 3 days after the onset of chest pain. In post-AMI period, MM3 reached a peak (518.6 U/L) first, on the average 14.0 hours after AMI, followed by MM2 (19.8 h, 640.5 U/L) and MM1 (28.7 h, 641.3 U/L). According to their faster decay from circulation, MM3 had higher fractional disappearance and appearance rates, followed by MM2 and MM1. The MM3/MM1 activity ratio rose beyond the upper limit, found in health subjects, about 3.5 hours after onset of symptom and peaked on an average 10.6 hours after AMI, even earlier than the peaks of all isoforms, CK and CK-MB. On the other hand, our findings indicated these changes in isoform composition can be of value in estimating the time elapsed since the onset of tissue damage; MM3 is the predominant isoform when the tissue necrosis is of relatively recent origin (5-15 h); MM2 is the dominant subband between 15 and 24 hours after AMI, whereas a predominant MM1 band would indicate a significantly longer time period since the injury occurred (24 hours or more). Thus, these characteristics make CK-MM isoforms an earlier and more sensitive indicator of acute release from necrotic myocardium and an effective mean of predicting the time of the onset of AMI.