CHANGES IN SERUM MYOSIN LIGHT-CHAIN-I FOLLOWING AORTOCORONARY BYPASS OPERATIONS

The changes in myosin light chain I (MLC I) following aortocoronary by pass were studied in 31 patients and the curves of these changes were classified into three different patterns. A peak level of 14.7 +/- 1.5 4 ng/ml was seen in seven patients on postoperative day (POD) 2 which decreased suddenly to less than twice the normal value by POD 7 (group 1). Another 19 patients showed a peak level of 20.7 +/- 16.5 ng/ml on POD 5, which decreased slowly and was still high even by POD 7 (group 2). The remaining five patients developed only a slight increase in t he MLC I level after the operation, with a peak value of 5.5 +/- 0.8 n g/ml (group 3). Creatine kinase myocardial band and glutamic oxaloacet ic transaminase also remained low in this group. No correlation existe d between the peak value of MLC I and the aortic cross-clamping time, or between the peak value of MLC I and the cardiopulmonary bypass time . Furthermore, the difference in cardiac output before and after the o peration did not significantly differ among the three groups. These fi ndings indicate that the measurement of MLC I is useful for diagnosing perioperative myocardial damage and may also be useful in the study o f myocardial protection.