The MB isoenzyme of creatine kinase as an indicator of severity of myocardial ischaemia.

86 patients with ischaemic heart-disease were assessed for the presence of the MB isoenzyme of creatine kinase (C.K.-MB). Raised C.K.-MB levels with normal total C.K. were found in 10 patients with a clinical picture, but no electrocardiographic evidence, of acute myocardial infarction. 4 of these patients later had an infarction, but the remaining 6 have remained undiagnosed. Of 26 patients with unstable angina, 11 (42%) had high levels of C.K.-MB in the presence of normal total C.K. Of 50 patients with effort angina and a positive ergometric stress test, 3 (6%) with crescendo angina had high C.K.-MB levels in the presence of normal total C.K. In patients with angina, myocardial necrosis was excluded by normal serum-myoglobin levels. In both groups with angina, those with raised C.K.-MB levels had a more severe clinical picture, greater depressions of the ST segment, and lower threshold to ergometry. Raised C.K.-MB levels may indicate myocardial ischaemia.