Determination of the origin of elevated plasma CPK after cardiac catheterization

Episodes of chest pain are not common in patients undergoing cardiac catheterization. The diagnostic implications of this symptom may be complicated by the occasional appearance of electrocardiographic changes mimicking those seen in acute myocardial infarction, and by the frequent elevation of conventionally measured serum enzymes. Exclusion of infarction is particularly important when coronary revascularization is contemplated. Since the MB CPK isoenzyme is relatively specific to myocardium, we assayed CPK isoenzymes in plasma samples from 184 patients undergoing cardiac catheterization to determine whether CPK elevations accompanying catheterization can be distinguished from those associated with myocardial infarction. Samples were obtained every 2 hr for 24 hr, and CPK isoenzymes quantified by a kinetic fluorometric method. Total plasma CPK increased in all patients (mean peak 0.238 +/- 0.042 (SD) IU/ml) but MB CPK remained normal in 181 patients (less than 0.005 IU/ml). In three remaining patients, MB CPK was elevated and myocardial infarction was confirmed by 99mTc (SN) pyrophosphate scan. Twelve patients after catheterization, in whom no intramuscular premedication was given, exhibited only minimal elevation of total plasma CPK. In contrast, 100 control patients with acute myocardial infarction exhibited peak total CPK activity averaging 0.833 +/- 0.037 (SD), and MB CPK was elevated in all cases (0.078 +/- 0.027 (SD) IU/ml). Thus, CPK elevations after catheterization reflect release of enzyme from noncardiac sources rather than from injured myocardium. Furthermore, increased plasma MB CPK activity may be considered a reliable index of myocardial infarction in patients undergoing cardiac catheterization.