Prospective Assessment of Presenting Serum Markers for Cardiac Risk Stratification

Objective: To quantify the association of initial ED serum cardiac markers with the risk for life-threatening events (LEs) or need for lifesaving interventions (Lis) or administration of IV nitroglycerin.
Methods: A prospective, observational study was performed using a cohort of hemodynamically stable, hospitalized patients (age > 25 years) presenting with nontraumatic chest discomfort. Patients with ST-segment elevation on their initial ECGs were excluded. Presenting serum samples were assayed for serum myoglobin and creatine kinase-MB isomer (CK-MB) using the Opus and Stratus systems. Target cases were defined as patients having LEs (e.g., cardiogenic shock, ventricular fibrillation, cardiac arrest), requiring Lis (e.g., intubation, cardioversion, pacing, reperfusion therapy), or needing IV nitroglycerin within 48 hours. Manufacturer's thresholds defined abnormal marker levels. Abnormal ECGs were defined using the Brush criteria.
Results: Of the 178 eligible patients, 44 (25%) were target cases . Most (55%) target cases had blood drawn for assays within four hours of chest discomfort onset. The relative risk and sensitivity of the serum markers and the ECG for target cases follow:
Of the seven patients with an LE/LI, six had blood drawn four hours or less after symptom onset; two LE/LI patients had abnormal myoglobin levels' no LE/LI patient had an abnormal CK-MB level.
Conclusions: Isolated serum myoglobin and CK-MB levels obtained at patient ED presentation were not strongly associated with the 48-hour risk for LEs, Lis, or the use of IV nitroglycerin. Future studies of risk stratification should address the merits of serial serum marker measurements that extend up to 12 hours beyond patient symptom onset.