Identifying low-risk patients within the observation zone of a 0/2-h high-sensitivity troponin diagnostic protocol for chest pain evaluation.

Background: High-sensitivity cardiac troponin (hs-cTn) based accelerated diagnostic protocols for suspected acute coronary syndrome (ACS) in the emergency department (ED) can classify up to 40 % of patients as intermediate-risk (the "observation zone"). Expert consensus pathways recommend further risk stratification with additional hs-cTn testing and clinical risk scores.

Methods: We conducted a retrospective cohort study of adult encounters for chest pain across 21 community EDs from January 1, 2023, to June 30, 2024. We assessed the test characteristics and efficacy (proportion identified as low risk) of two clinical risk strategies [History, ECG, Age, Risk Factors, and Troponin (HEART) pathway or the ED Assessment of Chest Pain Score Accelerated Diagnostic Pathway (EDACS-ADP)] in excluding 30-day myocardial infarction (MI) or death among patients classified as intermediate-risk by a 0/2-h hs-cTnI diagnostic protocol (Beckman Access hsTnI).

Results: We identified 11,178 intermediate-risk encounters, of which 789 (7.1 %) had 30-day MI or death. Both clinical risk strategies had high negative predictive value (NPV; EDACS-ADP 99.1 %, 95 % CI 98.5-99.4 %; HEART pathway 99.0 %, 95 % CI 98.1-99.5 %) but also low efficacy (14 % and 8 %, respectively). In contrast, objective testing alone (hs-cTnI <99th percentile and non-ischemic ECG) and ED discharge disposition had higher efficacy (31 % and 57 %) with slightly lower NPV (98.2 % and 98.1 %, respectively).

Conclusion: Both EDACS-ADP and the HEART pathway identified intermediate-risk patients with ≤1 % risk of 30-day MI or death, but with low efficacy. Objective testing or ED discharge disposition had notably higher efficacy, but require an acceptable "miss-rate" of ≤2 %.