We investigated whether the proportion of creatine kinase (CK) MM3 to total MM isoform, measured in a single blood specimen taken at 3 hours after starting intravenous administration of streptokinase to patients with developing myocardial infarction, would give reliable information on patency or occlusion of the infarct-related coronary artery.
Fifty-nine patients received streptokinase 1.5 χ 106 U intravenously within 6 hours of onset of prolonged chest pain and ST-segment elevation. Patency of the infarct-related coronary artery was assessed by arteriography at 2.6 ±0.3 (SD) hours after starting streptokinase. Creatine kinase MM isoforms were measured by chromatofocusing in blood taken at 3 hours after streptokinase.
A proportion of CKMM3 to total CKMM of greater than 50% was present in 34 of 34 patients (100%) with a patent, infarct-related artery at arteriography and whose peak total CK activity reached twice the upper normal limit for our laboratory (600 U/L). CKMM3/total CKMM was less than 50% in 14 of 18 patients (78%) in whom the infarct-related artery was occluded. In five of six patients with a nondiagnostic total CK rise (peak < 600 U/L), 3-hour CKMM3/total CKMM was less than 50% despite a patent artery. CKMM3 was not measurable in one patient.
A proportion of CKMM3/total CKMM of greater than 50% is highly sensitive for prediction of infarct artery patency at 3 hours after administration of streptokinase. However, the test used in this way is not reliable for patients with “prevented” myocardial infarction. Also, positive tests do occur in patients with angiographically occluded arteries, possibly signifying intermittent reperfusion and occlusion.