Quantitative and temporal relation between the release of myoglobin and creatine kinase and the evolution of vectorcardiographic changes during acute myocardial infarction in man

Abstract

The relation in time and magnitude between QRS vector changes (QRS-VD), ST vectors (ST-VM), and the cumulated release of myoglobin, total creatine kinase, and creatine kinase isoenzyme MB was studied. Seventy four patients with a first myocardial infarction and a history of symptoms of up to 5 h were included. Blood samples for enzyme analysis were taken every 4-6 h for 72 h and cumulated enzyme release was calculated from a monocompartmental first order model. QRS-VD and ST-VM were determined every 10 min for 24 h by computer analysis of Frank lead vectorcardiograms. Infarct sizes were visually determined from the different enzymatic and vectorcardiographic evolution curves. Eight patients were excluded from the analysis because they had a QRS width ≥120 ms or ill defined plateaus of the release curves. The relation between infarct sizes estimated from QRS-VD and total creatine kinase was r=0.62; QRS-VD and myoglobin release r=0.57; total creatine kinase and myoglobin release r=0.72, showing that these variables are good and complementary indices for estimating myocardial infarct size. Median infarct evolution curves were computed after the individual curves were normalised to 100%. ST-VM fell rapidly during the first 7 h to 40% of the initial values. QRS-VD and myoglobin release were closely associated and completed their development on average 15 h after the onset of symptoms. In contrast, the release of total creatine kinase and creatine kinase MB, which started 3-5 h after the onset of symptoms, was completed 26 h after the onset of symptoms. This shows that total creatine kinase and creatine kinase MB cannot be used as real time indices of infarct evolution. Infarct limiting treatment must be instituted within the first 6-8 h to be effective. The results further support the combined use of QRS vector changes and cumulated myoglobin release for monitoring myocardial infarct evolution and infarct size.