Individualized values for the disappearance rate parameter (Kd) in the enzymatic estimation of infarct size. A critique.

A mathematical model to measure infarct size from serial estimates of CPK has been developed by Shell et al. Norris et al. have recently introduced a modification of this method by calculating an individualized disappearance rate parameter (Kd) from the uniformly monoexponential portion of the CPK vs time curve. This modification is based on the assumption that when CPK is decaying monoexponentially, the amount of CPK appearing in the circulation is zero. This paper presents a mathematical analysis which shows that the method of Norris et al. is theoretically unsound, as the CPK appearance function may be significantly different from zero and yet CPK vs time may still be monoexponential. Their method may lead to erroneous results in the calculation of infarct size.