[CK MB versus total CK in the estimation of myocardial necrosis. Comparative kinetic analysis and evaluation of an immunological method].

It has been suggested that the adoption of a relatively specific marker of the myocardial cell, such as creatine kinase MB isoenzyme, can yield improved accuracy in estimating infarct size by serial serum sampling and compartmental analysis. Nevertheless, current methods for the evaluation of isoenzyme activity are cumbersome and unsuitable for clinical use. We have therefore employed a new test for the rapid determination of CK MB activity, based on the immunological inhibition of M subunities. In 19 patients not submitted either to intramuscular injection or to repeated defibrillations, a good correlation was found between indexes of necrosis based on MB and total CK determination (r = 0.94), with the cumulative MB release amounting to 16 +/- 4% of total CK. Significant differences were observed in 3 patients submitted to external cardiac massage (MB = 9 +/- 1% of total CK) thus suggesting a considerable extracardiac source of total CK due to the trauma of the skeletal muscle. The comparative kinetic analysis shows substantial differences between the two isoenzymes, not only concerning the greater disappearance rate of CK MB but, more significantly, related to a faster release of this isoenzyme from the myocardium, which has not been previously reported. The good correlations found between maximal appearance rate and cumulative enzyme release (r = 0.86) suggest that the former may represent an index of the rate of degradation of cellular membranes. Practical implications of these data are discussed.