Early diagnosis of acute myocardial infarction in patients without ST-segment elevation

Early identification of acute myocardial infarction (AMI) is necessary to i nitiate appropriate treatment. In patients presenting without ST-segment el evation, diagnosis is often dependent on the presence of elevated myocardia l markers. This study examines the ability of serial MB mass alone and in c ombination with myoglobin in diagnosing AMI in patients without ST-segment elevation within 3 hours of presentation. In all, 2,093 patients were admit ted and underwent serial marker analysis using myoglobin, creatine kinase ( CK), and CK-MB at 0, 3, 6, and 8 hours. AMI was diagnosed by a CK-MB greate r than or equal to 8.0 ng/ml and a relative index (RI) (CK-MB x 100/total C K) greater than or equal to 4.0. A total of 186 patients (9%) were diagnose d with AMI. The optimal diagnostic strategy was an elevated CK-MB + RI on t he initial or 3-hour sample or at least a twofold increase in CK-MB without exceeding the upper range of normal over the 3-hour time period (sensitivi ty 93%, specificity 98%). The combination of an elevated CK-MB + RI or myog lobin on the initial or 3-hour sample had a sensitivity of 94%, although sp ecificity was significantly lower, at 86%. Sensitivities and specificities after exclusion of the 242 patients with ischemic electrocardiographic chan ges were essentially unchanged. We conclude that most patients with AMI pre senting with nondiagnostic electrocardiograms can be diagnosed within 3 hou rs of presentation. (C)1999 by Excerpta Medica, Inc.