Serum isoforms of creatine kinase MM and MB in myocardial infarction. An appraisal of quantitative, clinical and pathophysiological information.

Using an electrophoretic method, the changes in the catalytic activities of three CK-MM isoforms (MM1, MM2, MM3) and two CK-MB isoforms (MB1, MB2) in the serum of 13 patients with acute myocardial infarction (AMI) have been monitored for 3 days after the onset of chest pain. In post-AMI period, MM3 reaches a peak first, 17 h after infarction (394 U/l), followed by MB2 (17.3 h, 190 U/l), MB1 (20.6 h, 82 U/l), MM2 (28.7 h, 637 U/l), and MM1 (32 h, 780 U/l). According to their faster decay from circulation, MB2 and MM3 have higher fractional disappearance rates (-0.035 and -0.026 per hour, respectively). The MM3/MM1 activity ratio rises beyond the upper limit found in healthy subjects within about 3 h after onset of symptoms and peaks 9.3 h after AMI, even earlier than peaks of isoforms. These characteristics make the ratio an earlier and more sensitive indicator of acute enzyme release from necrotic myocardium.