Isoelectric focusing of creatine kinase MM isoforms and its application for diagnosis of acute myocardial infarction.

CK MM isoforms (MM 3 having the highest isoelectric point, followed by MM 2, MM 1, and MM X) were measured in 35 patients with acute myocardial infarction (AMI) by isoelectric focusing on agarose gel. Blood samples were analysed every 2 h for the first 12 h, then every 4-8 h until 72 h after AMI. In the first sample, obtained 2.1 h after the onset of chest pain, the ratio of the isoforms MM 3:1 was 0.7 (range 0.2-1.8), equivalent to a normal value. Before the total CK exceeded normal, in 86% of the patients the ratio MM 3:1 rose to 2.2 (range 0.3-3.3). The maximal individual ratio MM 3:1 was 4 (range 0.9-12) after 7 h. It fell below 1 again after 27 h. Thus, the ratio MM 3:1 was useful in the early diagnosis of AMI by enzymatic methods and to estimate the time elapsed since the onset of infarction. Twenty patients with an open infarct vessel (angiographic data after thrombolytic therapy) showed similar peak enzyme activities as ten non-reperfused patients. They differed significantly in the time to the peak activity, mostly for CK MM 3 and CK MB (p less than 0.0005). A higher ratio CK MM 3:1 and a shorter time to the maximum CK MM 3 activity in reperfused patients helps to assess the success of thrombolytic therapy.