Resolving the observe zone: validation of the ESC 0/3-hour and the APACE criteria for NSTEMI triage.

BACKGROUND

High-sensitivity cardiac troponin tests have enhanced early myocardial infarction diagnosis, yet many patients still land in the observe zone (OZ). Guidelines suggest a 3-hour troponin measurement for those in the European Society of Cardiology (ESC) 0/1 hour-algorithm's OZ, but evidence on extended troponin testing times and their impact on diagnostic accuracy and outcomes remains sparse.

METHODS

Patients with suspected acute coronary syndrome were consecutively enrolled in a single-centre observational study. The triage protocol allowed an optional third troponin measurement at 3 hours or later to evaluate the performance and safety of two validated triage algorithms used to resolve the OZ.

RESULTS

Of the 4605 patients, 948 were triaged to the OZ (20.6%). The prevalence of non-ST-segment elevation myocardial infarction (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. For diagnosing NSTEMI, the ESC 0/3-hour criteria showed lower sensitivity (69.4%) than the criteria defined in the Advantageous Predictors of Acute Coronary Syndromes Evaluation (APACE) study (86.1%, p=0.053), with both having high negative predictive value (93.5% vs 87.5%, p=0.339). By definition, the ESC 0/3-hour algorithm categorises all patients into rule-in or rule-out, eliminating the need for an OZ, whereas 55.6% of patients remained in the OZ with the APACE criteria. Mortality rates in the OZ were similar across different timing protocols, with 30-day rates of 0.78% for third blood draws within 210 min (n=128) and 1.19% for those over 210 min (n=84); 3-year rates were 5.51% and 4.82%, confirming the safety of extended sampling.

CONCLUSIONS

Although the ESC 0/3-hour criteria have a lower sensitivity than the APACE criteria, it is by definition more effective because it does not leave patients in the OZ. Extending the timing for the third troponin measurement beyond 3 hours proves to be effective and safe, supporting its implementation in clinical practice.

TRIAL REGISTRATION NUMBER

NCT03111862.