Validation of the 0/3-h algorithm and the APACE criteria to triage patients in the observe-zone

While high-sensitivity cardiac troponin testing has improved the early diagnosis of myocardial infarction, a substantial number of patients remain in the observe zone (OZ). Recent guidelines recommend rapid protocols and a 3h cardiac troponin measurement in patients triaged to the OZ of the ESC 0/1h-algorithm, but evidence on extended troponin testing times and their impact on diagnostic accuracy and outcomes remains sparse.

Patients with suspected acute coronary syndrome were enrolled in a single-centre observational study. The ESC 0/1-hour protocol was used for triage, with an optional 3rd troponin measurement at 3 hours or later, to evaluate the performance and safety of two validated triage algorithms used to resolve the OZ including a version that extends the time interval for the third troponin measurement beyond 3 hours.

Of the 4,605 patients, 948 were triaged to the OZ (20.6%). The prevalence of NSTEMI within the OZ was 7.2%. 212 patients (22,3 % of OZ patients) had a third troponin measurement and were included in the comparative analysis. The overall sensitivity of the ESC 0/3-hour algorithm was lower at 69.4% compared to 86.1% (p=0.053) for the APACE algorithm, with both algorithms demonstrated similarly high negative predictive values (93.5% for ESC 0/3 and 87.5% for APACE, p=0.339). By definition, the ESC 0/3 hour algorithm categorises all patients directly into either rule-in or rule-out groups, eliminating the need for an OZ. In contrast, with the APACE algorithm 55.6% of patients remained in the OZ. Mortality rates in the OZ were similar across different timing protocols, with a 30-day mortality rate of 0.78% for patients with a third blood draw within 210 minutes (n=128) and 1.19% for those with the draw above 210 minutes (n=84). Over the 5-year follow-up, the overall mortality rates were 5.51% and 4.82% for the within-210 and above-210 groups, respectively, confirming the safety of the extended sampling interval.