The Importance of Identification of the Myocardial-Specific Isoenzyme of Creatine Phosphokinase (MB Form) in the Diagnosis of Acute Myocardial Infarction

Serial plasma determinations of the isoenzymes of CPK were performed in all patients (376) admitted to a coronary care unit during a 12-month period with diagnosis of possible acute myocardial infarction. Results were compared with data from other enzyme studies and from the electrocardiogram. An attempt was made to determine the incidence of falsely positive CPK-MB (myocardial-specific form). "No acute infarction" was diagnosed in all patients in whom neither total CPK nor the isoenzymes of LDH indicated myocardial necrosis, and in whom there were no QRS changes on ECG. Incidence of falsely negative CPK isoenzyme data was also determined. All patients, in whom total CPK was transiently elevated, and LDH 1 exceeded LDH 2 , and new QRS changes occurred, were termed "definite" acute infarction. CPK-MB form was present in all 55 of these (0% false negative). Therefore, determination of the isoenzymes of CPK by this method provides both a sensitive and specific indication of acute myocardial infarction.