Acute coronary syndrome rule-out strategies in the emergency department: an observational evaluation of clinical effectiveness and current UK practice.

Background: Numerous strategies have been developed to rapidly rule-out acute coronary syndrome (ACS) using high-sensitivity troponin. We aimed to establish their performance in terms of emergency care length of stay (LOS) in real-world practice.

Methods: A multicentre observational cohort study in 94 UK sites between March and April 2023. Recruitment was preferably prospective, with retrospective recruitment also allowed. Adults presenting to the ED with chest pain triggering assessment for possible ACS were eligible. Primary outcome was emergency care LOS. Secondary outcomes were index rate of acute myocardial infarction (MI), time to be seen (TTBS), disposition and discharge diagnosis. Details of ACS rule-out strategies in use were collected from local guidelines. Mixed effects linear regression models tested the association between rule-out strategy and LOS.

Results: 8563 eligible patients were recruited, representing 5.3% of all ED attendances. Median LOS for all patients was 333 min (IQR 225, 510.5), for admitted patients was 460 min (IQR 239.75, 776.25) and for discharged patients was 313 min (IQR 221, 451). Heterogeneity was seen in the rule-out strategies with regard to recommended troponin timing. There was no significant difference in LOS in discharged patients between rule-out strategies defined by single and serial troponin timing (p=0.23 and p=0.41). The index rate of acute MI was 15.2% (1301/8563). Median TTBS was 120 min (IQR 57, 212). 24.4% (2087/8563) of patients were partly managed in a same day emergency care unit and 70% (5934/8563) of patients were discharged from emergency care.

Conclusion: Despite heterogeneity in the ACS rule-out strategies in use and widespread adoption of rapid rule-out approaches, this study saw little effect on LOS in real-world practice. Suspected cardiac chest pain still accounts for a significant proportion of UK ED attendances. ED system pressures are likely to be explanatory, but further research is needed to understand the reasons for the unrealised potential of these strategies.