The nature of disappearance of creatine kinase from the circulation and its influence on enzymatic estimation of infarct size.

Abstract

Continued progress in estimating myocardial ischemic injury from analysis of plasma enzyme time-activity curves requires improved characterization of processes affecting release from the heart, transport and disappearance from the circulation. To determine whether the true disappearance rate (Kd) of creatine kinase (CK) is accurately reflected by the rate of elimination (ke) from blood, time-activity curves were evaluated in 40 conscious dogs after induced myocardial infarction, bolus injection or slow i.v. infusion of CK extracted from myocardium and CK harvested from plasma. The 2 CK preparations were compared by cellulose acetate electrophoresis, radioimmunoassay, gel chromatography and stability in vitro. Plasma CK time-activity curves after i.v. injections of CK conformed more closely to double than to single-exponential curves (with average SD only 42% as large), suggesting distribution in at least 1 extravascular compartment. Parameters of a 2-compartment model obtained from the double-exponential curve provided estimates of kd markedly greater than ke. Calculations based on observed plasma values and these estimates of kd accounted for 2-fold more CK released from the heart after infarction than that accounted for by calculations utilizing ke. The decline of plasma CK after myocardial infarction was 60% slower than the decline after i.v. enzyme injections. The relatively slow decline after myocardial infarction appears to be due to differences between enzyme extracted from the heart and enzyme released endogenously into plasma and to continuing release to CK from the ischemic heart relatively late after coronary occlusion.