Cardio-specific serum enzyme CK--MB following physical exercise in acute myocardial infarction.

The possible harmful effect of physical activity on the extent of myocardial damage in patients with fresh myocardial infarction (AMI) has been a matter of debate. In this paper, serial determinations of serum creatine kinase (CK) isoenzymes are presented from 20 unselected patients with AMI, in 14 of them complicated by congestive heart failure or/and significant rhythm disturbances. During the acute phase, the cardiospecific MB-isoenzyme of CK in all patients rose above the upper reference limit of 30 U/l, the peak values ranging from 39 to 741, and returned to normal range within a few days. During the third week a maximal, symptom-limited exercise test was performed, with renewed serial determinations of CK-isoenzymes. Following the exercise an ST-segment deviation in the ECG was noted in 14 patients, anginal pain in 4, and a significant rise in serum CK--MM activity in 9 patients, whereas the CK--MB isoenzyme remained at zero level in all 20 patients. Thus, no evidence was found that even a maximal physical effort during the third week after AMI did cause any myocardial damage.