Significance of an Indeterminate Troponin I in Patients Evaluated for Chest Pain in an Emergency Department Observation Unit

Abstract

Previous studies have suggested that patients with an indeterminate troponin I (TnI) in the emergency department (ED) are significantly more likely to be diagnosed with acute myocardial infarction (MI). The role of the ED observation unit (EDOU) in the evaluation of these patients is unclear. We sought to determine the risk of MI and revascularization in chest pain patients with an indeterminate TnI in the ED, who were placed in an EDOU. We performed a prospective evaluation with 30-day follow-up for all chest pain patients placed in the University of Utah EDOU between June 1, 2009 and May 31, 2012. The EDOU excludes patients with a positive TnI, significant electrocardiogram changes, or active chest pain; however, the EDOU is utilized for further evaluation of patients who have an initial indeterminate TnI (0.06 ng/mL-0.49 ng/mL) with serial TnI measurements, cardiology consult, and potential provocative testing. We identified all patients who had an indeterminate TnI on initial testing in the ED. Primary outcomes were MI, revascularization with cardiac stent or coronary artery bypass graft, and death. We evaluated 1276 chest pain patients in the EDOU over the 3-year study period (average age: 54.1 years, 54% female). Fifty-eight patients (4.5%) had an initial indeterminate TnI. There were no deaths or adverse outcomes in the EDOU among those with an indeterminate TnI, and none of these patients developed a positive TnI during their hospital stay or 30-day follow-up. Patients with an indeterminate TnI had a higher rate of inpatient admission from the EDOU (24.1% vs. 10.3%; P=0.001). Among those with an indeterminate TnI, 8.6% underwent revascularization, while the rate of revascularization or MI was 2.9% among those who did not have an initial indeterminate TnI (P=0.032). Patients evaluated in our EDOU for chest pain with an initial indeterminate TnI did not develop subsequent MI. However, these patients had an increased rate of revascularization and inpatient admission compared with controls. While our experience suggests that patients with an indeterminate TnI may be safely evaluated in an observation setting, EDOUs which treat only low-risk chest pain patients may wish to recommend inpatient admission for this patient group.