Plasma creatine kinase isoenzyme determinations in infants and children. Characterization in normal patients and after cardiac catheterization and surgery.

In adults, plasma elevations of creatine kinase isoenzymes are highly specific for myocardial necrosis, however, the diagnostic sensitivity and specificity of MB CK in children have not been determined. Accordingly, we analyzed the CK isoenzyme activity in serial plasma samples from 147 patients, aged 2 days to 18 months. Forty-two patients underwent routine checkups and served as controls. Fifty-seven patients underwent cardiac catheterization for congenital heart disease, an additional 16 underwent non-cardiac surgery, and 32 cardiac surgery. Blood samples were obtained prior to surgery and catheterization and q6H x 3 thereafter. Total plasma CK and MB CK in normals averaged 62 +/- 22 (SD) and 1.7 +/- 0.8 IU/L respectively. Despite a fivefold increase in total plasma CK after catheterization and surgery, MB CK remained normal. After cardiac surgery, total CK increased from 68 +/- 18 to 905 +/- 231 IU/L, and MB CK increased from 1.7 +/- 0.6 to 13 +/- 7 IU/L. Thus, MB CK is specific for cardiac injury and would be a valuable adjunct in the diagnosis of myocarditis or in assessing interventions to minimize cardiac injury during surgery.