Combined cardiac marker approach with adjunct two-dimensional echocardiography to diagnose acute myocardial infarction in the emergency department

Study objective: To evaluate a combined cardiac marker approach with adjunct two-dimensional echocardiography in diagnosing acute myocardial infarction (AMI) in the emergency department. Methods: This prospective, cohort study enrolled 190 patients aged 18 years and older who presented to the ED of a county teaching hospital and were admitted with chest pain suggestive of AMI. A standardized history and physical examination were performed. Serum sampling for myoglobin and creatine kinase-MB (CK-MB) was done at the time of presentation (time 0) and 3 hours later (time 3 hours). An echocardiographic study was obtained, and a left ventricular wall motion score was derived. Results: Using World Health Organization criteria, 21 patients (11.2%) with AMI were identified. The serum markers were found to be clinically and statistically different between AMI and non-AMI groups at both time 0 and time 3 hours. Receiver operator characteristic curves were used to determine a 'positive' myoglobin level at 88.7 ng/mL or higher at either time point, and a 'positive' CK-MB level at 11.9 ng/mL or higher; these were used as the optimal cutoff values to predict AMI in the ED. Serum myoglobin was a more sensitive marker (90.5%) than CK-MB (81.0%). However, CK-MB was more specific (99.4%) than myoglobin (88.4%). A combination of both tests, which was rated positive if either test was positive, was a superior predictor overall, with a 100% capture rate of AMI patients and a 91.2% specificity. No significant difference in echocardiographic scores was appreciated in the AMI group compared with the non-AMI group (16.9±1.5 versus 15.3±.5, respectively; P=.3252). Conclusion: Serum myoglobin shows greater sensitivity but is less specific than CK-MB in the early detection of AMI. Use of a combination of both rapid assays during a 3-hour time period in the ED appears to be superior to use of either enzyme assay alone. Two-dimensional echocardiography does not appear to be helpful in diagnosing AMI in the ED.