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

Abstract Background Acute chest pain in primary care often results in defensive and unnecessary hospital referrals due to the limited ability to rule out an acute myocardial infarction (AMI) outside of hospital. In a previous prospective observational study (OUT-ACS; One-hoUr Troponin in a low-prevalence population of Acute Coronary Syndrome), we demonstrated that the ESC 0/1-hour algorithm for high-sensitivity cardiac troponin T (hs-cTnT) would be safe and cost-effective if implemented to assess low-risk patients with chest pain in emergency primary care. Purpose We evaluated the real-world applicability, personnel adherence, and disposition of low-risk patients with chest pain following the implementation of the ESC 0/1-hour algorithm in emergency primary care. Methods In April 2023, the ESC 0/1-hour algorithm for hs-cTnT was implemented at a large emergency primary care clinic in Norway. The clinic is located close to a hospital, enabling the patient to wait at the clinic while blood samples are analysed for hs-cTnT at the hospital laboratory. For the following six months, all patients ≥18 years with acute non-traumatic chest discomfort, offered hs-cTnT measurements at the clinic, were anonymously registered, including their discharge diagnoses and disposition from the clinic. By applying the ESC 0/1-hour algorithm, patients were assigned to rule-out, rule-in or further observation. Patients in the observation group were offered a 4-hour hs-cTnT measurement before a final decision. Results During the six-month period, 10.3% (n=3,053/29,631) of the clinic's consultations involved chest complaints. Hs-cTnT measurements were conducted in 32.6% (n=995/3,053) with a median age of 58 years (IQR 45-68), 50.6% being female. A single hs-cTnT <5 ng/L, sampled ≥3 hours since symptom onset, triaged 24.1% (n=240/995) of the patients towards the rule-out group, increasing to 63.8% after adding a 1-hour measurement. In the rule-in group (n=42/995, 4.2%), 16 patients were diagnosed with an AMI. The intermediate observation group (n=318/995, 32.0%, 4 AMIs) was reduced to 23.0 % after a 4-hour hs-cTnT measurement. Healthcare personnel adhered well to the algorithm, with a median sampling interval of 63 minutes (IQR 60-66) and 4.5 hours (IQR 4.1-5.5) for the 1- and 4-hour measurements, respectively. The algorithm was misinterpreted or overruled in 8.8% of the cases. Ultimately, only 14.8% required hospital transfer following troponin assessment at the clinic. The remaining patients were sent home or managed in the outpatient setting. Conclusions The OUT-ACS strategy, utilizing a 0/1/4-hour algorithm for hs-cTnT measurements in emergency primary care, is safe, effective and applicable, and the strategy contributes to reduced hospital referrals for low-risk patients with chest pain.0/1/4-hour algorithm for hs-cTnTDisposition