Rapid rule-out of acute myocardial infarction using the 0/1-hour algorithm for cardiac troponins in emergency primary care: the OUT-ACS implementation study

BACKGROUND: Acute chest pain has a high hospital referral rate due to the limited ability to exclude acute myocardial infarction (MI) in primary care. We aimed to evaluate the effectiveness of implementing the European Society of Cardiology (ESC) 0/1-hour algorithm for high-sensitivity cardiac troponin T (hs-cTnT) testing in emergency primary care. METHODS: In a prospective study (April-October 2023), the ESC 0/1-hour algorithm for hs-cTnT was implemented at the main emergency primary care clinic in Oslo, Norway. All consecutive patients ≥ 18 years with acute non-traumatic chest pain having hs-cTnT measurements done were registered. The patients were assigned to MI rule-out, rule-in, or further observation using the algorithm. Patients in the observation group had a 4-hour hs-cTnT measurement done. The outcome measures were the proportion of patients conclusively assessed by the protocol, personnel adherence, reduction in length of stay (LOS) compared to the previous 0/4-hour protocol (historical cohort), and disposition. RESULTS: During six months, hs-cTnT measurements were conducted in 32.6% (995/3053) of chest pain patients (median age 58 years (IQR 45-68); 50.6% female). A single hs-cTnT measurement assigned 24.1% (n = 240/995) towards MI rule-out, suitable for early discharge, increasing to 63.8% after adding a 1-hour measurement. The observation group (319/995, 32.1%) was reduced to 23.0% (229/995) after a 4-hour measurement. A total of 77.0% of the patients were conclusively assigned to either rule-out or rule-in group. The personnel adhered well to the new protocol, with a median 1-hour sampling interval of 63 min (IQR 60-66) and 4.6 h (IQR 4.1-5.5) for the 4-hour sample. The protocol was misinterpreted or overruled in 8.6% of the cases. Compared to the previous 0/4-hour protocol, LOS was reduced by -2.2 h (95% confidence intervals - 2.6 to -1.7). After completed assessment at the clinic, 14.8% were transferred to hospital, where 20 patients were diagnosed with an MI. The remaining patients were sent home or managed in the outpatient setting; any occurrence of MIs in this group is unknown. CONCLUSIONS: The ESC 0/1-hour algorithm effectively assesses low-risk acute chest pain in emergency primary care, reinforcing its gatekeeper role by managing these patients at a lower level of care.