Emergency Medical Services
Background: Chest pain is a common reason for ambulance transport. However, paramedics lack validated tools for risk stratification. The modified History, ECG, Age, Risk factors, Troponin score (mHEART) is validated for Emergency Department use, but has yet to be prospectively tested in the prehospital setting.The objective of this study is to establish the feasibility and performance of prehospital mHEART assessment using point-of-care (POC) troponin (cTn).
Methods: A prospective observational study of adults with non-traumatic chest pain was conducted in 3 Emergency Medical Services agencies (12/2016-1/2018). Paramedics excluded patients with ST-elevation myocardial infarction (STEMI) on ECG. During ambulance transport paramedics initiated intravenous access, drew blood, used a POC device (i-STAT; Abbott Laboratories*) to measure cTn, and calculated mHEART on each patient. Patients were classified as non-low risk if they had a mHEART >3 or elevated POC cTn. In the hospital core lab, prehospital blood was analyzed for cTn (Beckman Coulter or Siemens). The primary outcome was index major adverse cardiac events (MACE: composite of cardiac death, myocardial infarction, and coronary revascularization), which was adjudicated by 3 experts blinded to paramedic assessments and POC cTn. Test characteristics of mHEART for detection of MACE were calculated.
Results: During the study period, 506 patients were accrued, withindex MACE occurring in 16.8% (85/506). Prehospital POC cTn measurement was attempted in 99% (501/506) of patients, with 83.2% (421/506) receiving numeric results and 15.8% (80/506) receiving error codes. mHEART assessments were completed in 87.5% (443/506) of patients. Prehospital mHEART with POC cTn was 91.1% (95% CI 82.6-96.4%) sensitive for detection of index MACE with a negative predictive value (NPV) of 94.4% (95% CI 88.7-97.7%). However, paramedic mHEART combined with core lab cTn from prehospital blood yielded 100% sensitivity and NPV for index MACE.
Conclusion: POC cTn measurement and mHEART calculation by paramedics during ambulance transport is feasible. The sensitivity for MACE of mHEART with POC cTn was moderate and improved when paired with core lab assays. These results suggest that structured prehospital risk assessments may facilitate earlier identification of patients with MACE.
*i-STAT use in a moving ambulance is off-label.