Selection of a biochemical marker for the early detection of acute myocardial infarction

Optimum use of thrombolytic therapy for patients with acute myocardial infarction (MI) requires an early diagnosis so that agents can be administered as early as possible after the onset of chest pain. Serum myoglobin and creatine kinase-MM (CK-MM) isoforms have been found to be sensitive and early markers for MI compared to CK-MB isoenzyme. Serum myoglobin, CK-MM isoforms and CK-MB activity were measured by radioimmunoassay, isoelectrofocusing and agarose gel electrophoresis, respectively, in serial serum specimens from patients diagnosed with acute MI, burn and trauma. Total CK and total lactate dehydrogenase were also monitored and were analyzed by an autoanalyzer procedure. Both the MM3/MM1 ratio and the myoglobin level were elevated even in the first sample in 16 of 20 MI patients and within 1.2 hr in most of the other cases; CK-MB was elevated in the first sample only in 50% of the cases and took four to 6.5 hr in some cases to show above normal levels. Also, the MM3/MM1 ratio and serum myoglobin reached peak levels four to six hr earlier than CK-MB. There was no significant difference (p>0.1) between the time of appearance of elevated MM3/MM1 ratio and myoglobin level. The duration and the magnitude of elevation of these markers, however, were different from each other, with myoglobin remaining elevated significantly longer than MM3/MM1 ratio. Thirteen of 18 burn patients and 7 of 12 trauma patients had above-normal MM3/MM1 ratio and myoglobin level; therefore, evidently CK-MM isoforms and myoglobin are nonspecific in burn and trauma patients. Because of the availability of rapid methods of testing for serum myoglobin and its longer duration of elevation, serum myoglobin is recommended as the test of choice for early detection of MI.