Limitation of enzymatic models for predicting myocardial infarct size

The possibility of predicting myocardial infarct size from early enzyme measurements was studied using a physiological two compartment distribution model. Based on this the time dependent appearance function in plasma was calculated for creatine kinase, aspartate aminotransferase, and lactate dehydrogenase in 29 patients suffering from acute myocardial infarction. On average, the appearance function of the three enzymes started four hours after the onset of symptoms, and the maximum was reached after 12 hours for creatine kinase, 13 hours for aspartate aminotransferase, and 22 hours for lactate dehydrogenase. The cumulated appearance function was used as an acceptable estimate of infarct size. The prediction of infarct size from defined points of the appearance function curve for each of the three enzymes was attempted according to a set schedule during the first 25 hours after the onset of myocardial infarction. The prediction using creatine kinase was superior to the other enzymes. Even so, a reliable prediction could only be established at the very earliest from nine hours and this is too late, as irreversible loss of myocardium occurs rapidly after the onset of symptoms. This, together with the fact that other models have unacceptable variability of the prediction, lead to the conclusion that enzymatic predictive models are of no practical value in clinical intervention studies to reduce infarct size.