Prehospital Blood Collection for High Sensitivity Cardiac Troponin Measurement in Patients with Acute Chest Pain

OBJECTIVES High sensitivity cardiac troponin (hs-cTn) measures are used in the emergency department (ED) to evaluate patients with acute chest pain. Prehospital hs-cTn measurement could facilitate earlier rule-out of myocardial infarction (MI). The objective of this study is to assess the performance of prehospital blood draw for hs-cTnI measure alone, in combination with hs-cTnI measured at ED arrival, and incorporating the Myocardial Ischemic Injury Index (MI3) machine learning algorithm to rule-out index MI.METHODS We conducted a pilot prospective observational cohort study among adult emergency medical services (EMS) patients with acute, non-traumatic chest pain. Two third-service EMS agencies and two tertiary care EDs in North Carolina participated. Demographics and initial ECG findings were collected. Blood was obtained prehospital and on ED arrival for hs-cTnI measurement. The clinical outcome was adjudicated index visit MI. Efficacy (percentage of patients with index MI ruled-out) and negative predictive value (NPV) for index MI were determined for the following strategies: 1) a very-low single prehospital hs-cTnI, 2) serial hs-cTnI change (delta) at the prehospital and arrival timepoints, 3) MI3 incorporating prehospital hs-cTnI alone and 4) MI3 incorporating prehospital and arrival hs-cTnI.RESULTS Of the 75 patients enrolled, 53.3% (40/75) were women, 32.0% (24/75) were Black patients, and the mean age was 62.2 ± 15.7 years. Index MI occurred in 8.0% (6/75). Prehospital hs-cTnI below the limit of quantification (≤2.7ng/L) had an efficacy of 46.7% (35/75) with an NPV of 100% (95%CI 90.0%-100%) for index MI. A prehospital and arrival hs-cTnI delta ≤3 had an efficacy of 84.3% (43/51) with an NPV of 97.7% (95%CI 87.7-99.9%) for index MI. The standard low-risk MI3 threshold <1.6 with a single prehospital hs-cTnI had an efficacy and NPV for index MI of 76.0% (57/75) and 96.5% (95%CI 87.9-99.6), respectively. Finally, the standard low-risk MI3 threshold incorporating both prehospital and arrival hs-cTnI had an efficacy of 70.6% (36/51) and NPV of 100% (95%CI 90.3-100%) for index MI.CONCLUSIONS Strategies using prehospital blood for hs-cTnI measurement alone and MI3 with prehospital and arrival hs-cTnI safely identified a large percentage of patients ruled-out, warranting further investigation in a larger trial.