Plasma MB creatine phosphokinase (CPK) activity is consistently elevated following myocardial infarction (MI). To determine whether elevations of plasma MB CPK activity is a specific index of myocardial injury, CPK and isoenzymes were assayed by a quantitative kinetic fluorometric technique in fresh organs obtained at surgery. Analysis of CPK isoenzymes showed myocardium to be essentially the only organ with MB CPK.
Operative procedures included thoracic, neck, genitourinary, and orthopedic surgery. Total plasma CPK activity increased in all patients; however, MB CPK activity was not elevated. Thus, (1) the heart appears to be the only organ that is capable of liberating substantial amounts of MB CPK into plasma; (2) in spite of notably increased CPK activity after cardiac surgery, MB CPK activity is not elevated; and (3) increased MB CPK activity is a reliable index of MI in postoperative patients.
(Arch Intern Med 136:421-424, 1976)