Myoglobin levels at 12 hours identify patients at low risk for 30-day mortality after thrombolysis in acute myocardial infarction: A Thrombolysis in Myocardial Infarction 10B substudy

Objective: We sought to identify, by use of serum cardiac markers, patients at low risk for 30-day mortality after ST-segment elevation myocardial infarction. Background: Baseline cardiac markers are currently used to identify patients at increased risk for short-term events. We hypothesized that serum markers measured after treatment could identify patients at low risk for 30-day mortality. Methods: A total of 839 patients from the Thrombolysis in Myocardial Infarction (TIMI) 10B study had myoglobin, cardiac-specific troponin-I, creatine kinase (CK)-MB measurements at the following time points; baseline, 90 minutes, and 3 and 12 hours after thrombolysis. By use of receiver operating characteristic analysis, thresholds were derived to predict 30-day mortality with at least 95% negative predictive value. Results: Ninety minutes after thrombolysis myoglobin was superior to troponin-I or CK-MB in identifying patients at low risk for mortality. The 30-day mortality for 12-hour myoglobin ≤239 ng/mL was 1.4% compared with 9.1% for levels >239 ng/mL (P < .001). For 12-hour troponin-I (threshold 81.5 ng/mL), mortality was 1.9% versus 6.6% (P = .001) if above threshold; similarly for CK-MB at 12 hours (threshold 191 ng/mL) it was 3.3% versus 7.9% (P = .02). Multivariate analysis of baseline and posttreatment cardiac markers, age, sex, infarct artery location, and 90-minute TIMI flow grade identified only 12-hour myoglobin among the cardiac markers as independently predicting a low 30-day mortality (odds ratio 0.11, 95% confidence interval 0.02-0.50, P < .004). Conclusion: Serum cardiac markers can identify greater than two thirds of patients at low risk for 30-day mortality. A low 12-hour myoglobin level (≤239 ng/mL in this substudy) identifies such patients at low risk and could potentially assist in early risk stratification and triage after ST-segment elevation myocardial infarction.