Serial Creatine Kinase‐MB Results Are a Sensitive Indicator of Acute Myocardial Infarction in Chest Pain Patients with Nondiagnostic Electrocardiograms: The Second Emergency Medicine Cardiac Research Group Study

Objective : To determine the test performance characteristics of serial creatine kinase‐MB (CK‐MB) mass measurements for acute myocardial infarction (MI) in patients presenting to the ED with chest pain and nondiagnostic ECGs. Methods : A prospective, observational test performance study was conducted. Hemodynamically stable patients aged ≥25 years with chest discomfort, but without ECGs diagnostic for MI, were enrolled at 7 university teaching hospitals. Presenting ECGs showing >1‐mV ST‐segment elevation in ≥2 electrically contiguous leads were considered diagnostic for MI; patients with diagnostic ECGs on presentation were excluded. Real‐time, serial CK‐MB mass levels were obtained using a rapid serum immunochernical assay at the time of ED presentation (0‐hour) and 3 hours later (3‐hour). The following testing schemes were evaluated for their sensitivity and specificity for detection of MI during patient evaluation in the ED: 1) an elevated (≥8 ng/mL) presenting CK‐MB level; 2) an elevated presenting and/or 3‐hour CK‐MB level; 3) a significant increase (i.e., ≥3 ng/mL) within the range of normal limits for CK‐MB concentrations during the 3‐hour period (A CK‐MB); andor 4) development of ST‐segment elevation during the 3 hours (second ECG). Results : Of the 1,042 patients enrolled, 777 (74.6%) were hospitalized, including all 67 MI patients (8.6% of admissions). As a function of duration of time in the ED, the test performance characteristics of serial CK‐MBs for MI (and cumulative data for the additional ECG) were: 0‐hour CK‐MB Plus 3‐hour CK‐MB Plus A CK‐MB Plus Second ECG Sensitivity 38/67 = 57% 59/67 = 88% 62/67 = 93% 64/67 = 96% (95% CI) (44–69%) (78–95%) (83–98%) (88–99%) Specificity 9431976 = 97% 9351976 = 96% 9291976 = 95% 9311976 = 95% (95% CI) (95–98%) (94–97%) (94–96%) (94–97%) The 0‐hour to 3‐hour CK‐MB positive and negative predictive values were 52% to 55% and 96% to 99%, respectively. The sensitivities of serial CK‐MB results as a function of the interval following chest discomfort onset were: Interval Since Onset Sensitivity (95% CI) Interval Since Onset Sensitivity (95% CI) Less than 3 hours 38% (21–58%) 6 hours to 12 hours 92% (78–98%) 3 hours to 6 hours 75% (60–87%) More than 12 hours 100% (77–100%) Conclusion : Serial CK‐MB monoclonal antibody mass measurements in the ED can identify MI patients with initially nondiagnostic ECGs. CK‐MB sensitivity significantly increases over 3 hours of observation of stable chest discomfort patients in the ED; it also increases as a function of the total interval from onset until enzyme measurement.