Size estimation of acute myocardial infarction from serial serum myoglobin observations with due consideration of individual differences in basic kinetics

Abstract

Thirty-three consecutive patients suffering from acute myocardial infarction were studied. Serial serum myoglobin and CK-MB measurements were made, and in seven patients individual kinetic constants for myoglobin were available from previous single injection studies. A two-compartment model for myoglobin kinetics was used for infarct size estimation. Given values for the basic kinetic constants (elimination rate constant, exchange rate constants, and distribution volume), the adjustment of a flexible, parameterized ‘blood-appearance rate-function’, Ø_AMI, (mg·h⁻¹), allowed estimation of start-time (t₀), peak-time (t_peak) and end-time (t_end) of myoglobin inflow into blood from the infarct area, in addition to the total cumulative release (A), which was used as a measure of infarct size.

Use of patient-mean values for the kinetic constants caused a mean difference in estimated ‘infarct size’ of 34% (n = 7). Individual estimation of the elimination rate constant from the ‘final slope’ of the serum myoglobin curve could neither be recommended from a theoretical point of view nor from the practical outcome of numerical calculations; the ‘true’ elimination rate constant is underestimated by a factor of about 10 on average.

Good correlation was found between our myoglobin estimates of ‘infarct size’ (using patient-mean kinetic constants), and independent estimates from serial serum CK-MB data, as calculated by the use of the method by Sobel et al.

Large inter-individual variations were found in the estimated infarct parameters, a circumstance which is of special interest in evaluation of therapeutic intervention studies on AMI-patients, and in infarct size prediction calculations.

Key Words:

• acute myocardial infarction
• CK-MB
• infarct parameters
• myoglobin
• two-compartment model