Myoglobin concentrations and muscle-enzyme activities in serum after myocardial infarction and cardiac arrhythmia.

Sera from patients with myocardial infarction and cardiac arrhythmias were analyzed for myoglobin concentration and the activities of total creatine kinase, creatine kinase isoenzyme-2, and lactate dehydrogenase isoenzyme-1 at the time of hospital admission and during the first few days of hospitalization. The nine patients with a final diagnosis of myocardial infarction had abnormally high values for total creatine kinase, creatine kinase-2, lactate dehydrogenase-1, and myoglobin. Myoglobin concentrations were highest on admission in six patients and on the day after admission in the other three patients. Creatine kinase-2 manifested maximum activity on the day after admission for all patients with myocardial infarction. Lactate dehydrogenase-1 did not reach maximal values until the second or third day after admission. The six patients with arrhythmias did not show any significant increases in creatine kinase-2 or lactate dehydrogenase-1. Myoglobin and total creatine kinase, however, were increased in the four patients who had received cardioversion. The specificity and diagnostic usefulness of these serum measurements are discussed.