Rapid and safe discharge from the emergency department: A single troponin to exclude acute myocardial infarction

Objective: To determine variables that could facilitate safe discharge from the ED following a single high-sensitivity troponin I (HsTnI) result to exclude acute myocardial infarction (AMI). Methods: A retrospective cohort study was performed at a tertiary hospital of all patients that had serial HsTnI performed within 12 h of arrival to the ED over a 3 year period. The primary exposure variable of interest was a very low troponin initial result (HsTnI <5 ng/L). Medical record review and risk stratification score calculations were undertaken for all patients with the exposure variable of interest and an abnormal second troponin measurement (HsTnI ≥16 ng/L in women and HsTnI ≥26 ng/L in men). Results: There were 11 970 patients who presented between 1 July 2013 and 30 June 2016 that had serial HsTnI measurements performed. Of these, 4172 (34.9%) patients had an initial HsTnI measurement <5 ng/L. Of the patients with an initial HsTnI <5 ng/L that met inclusion criteria, 56 (1.3%) had a second troponin result above the 99th percentile and 32 (0.8%) cases of non-ST elevation myocardial infarction were diagnosed as well as 15 (0.4%) cases of ST elevation myocardial infarction. There were 44 (93.6%) of all AMI cases that met criteria for high-risk presentations under the National Heart Foundation of Australia guidelines. The negative predictive value of an initial HsTnI <5 ng/L to exclude AMI was 98.9% (95% confidence interval 98.5–99.1). Conclusions: This supports the utilisation of a rapid rule out strategy to exclude AMI for patients that have an initial HsTnI measurement <5 ng/L in conjunction with a robust risk assessment.