Discussion

The systematic review suggests that the use of POC troponin assays alone are insufficiently sensitive to rule out AMI in the prehospital settings. Six studies that evaluated the diagnostic accuracy of POC cTn testing in the prehospital settings were found. These findings show that prehospital troponin testing has a sensitivity ranging from 26.5% to 91.0% and NPV up to 94.9% for the diagnosis of AMI.^{Reference Sorensen, Terkelsen and Steengaard6-Reference Stopyra, Snavely and Scheidler12}

One of the most challenging tasks for paramedics in the prehospital setting is the diagnosis of AMI. Treatment for ACS or “rule out” could be initiated in the prehospital setting based on the ECG, the patient history of risk factors, blood pressure, and heart rate. Different prehospital studies show only 5%-18% of initial prehospital ECGs demonstrate STEMI.^{Reference Di Serio, Lovero and Leone11,Reference Svensson, Isaksson, Axelsson, Nordlander and Herlitz13-Reference Pedersen, Stengaard and Friesgaard16} This might lead to missed or delayed diagnosis of non-ST-elevation AMI, leading to treatment delay and poorer outcomes. Previously, many studies have evaluated cTn testing in the prehospital setting. These studies have focused on different aspects rather than the diagnostics accuracy of it, such as prognostication, and the association between the elevation of creatine kinase-myocardial band isoenzyme (CK-MB) or cTn and ST-segment elevation or ACS.^{Reference Svensson, Isaksson, Axelsson, Nordlander and Herlitz13,Reference Svensson, Axelsson, Nordlander and Herlitz17,Reference Svensson, Axelsson, Nordlander and Herlitz18} Interestingly, those studies reported that STEMI was strongly associated with elevation of CK-MB and cTn, which is significantly related to both ACS and AMI.^{Reference Svensson, Isaksson, Axelsson, Nordlander and Herlitz13,Reference Svensson, Axelsson, Nordlander and Herlitz17} In addition, three studies were conducted to evaluate the feasibility and reliability of prehospital troponin POC.^{Reference Sorensen, Terkelsen and Steengaard6,Reference Stengaard, Sorensen and Ladefoged8,Reference Di Serio, Lovero and Leone11,Reference Venturini, Stake and Cichon19} The authors of these studies showed that POC troponin testing by paramedics is feasible, reliable, and recommended, implementing POC troponin testing in the prehospital emergency settings by paramedics to facilitate triage and risk stratify with a suspected AMI patient. So far, there is no solid evidence to show the effect on treatment and outcome for patients with suspected AMI when using biomarker values to triage and initiate treatment in the prehospital emergency environment.^{Reference Sorensen, Terkelsen and Steengaard6,Reference Svensson, Isaksson, Axelsson, Nordlander and Herlitz13,Reference Ecollan, Collet and Boon20} Also, there are further troponin studies in the prehospital setting; however, in those studies, blood samples were obtained by paramedics in ambulances but only tested later in the hospital using central laboratory high-sensitivity assays.^{Reference Slagman, Searle, Muller and Mockel21-Reference Ishak, Ali and Fokkert24}

This systematic review focused on evaluating the diagnostic accuracy of POC cTn assays when used in the prehospital setting. An earlier systematic review by Nehme, et al^{Reference Nehme, Boyle and Brown25} aimed to evaluate the diagnostic accuracy of clinical prediction rules for potential use in a prehospital emergency environment, using data that “were not reliant on tests unavailable out of the hospital,” but found no evidence of any rules that could be used in practice. Since that time, studies have evaluated the History, ECG, Age, Risk Factors, and Troponin (HEART) score, a modified HEART score, and a History, ECG, Age, and Risk Factors (HEAR) score (the HEART score without requiring cTn testing) in the prehospital setting, albeit without using a POC cTn device to test prehospital blood samples.

A study by Stopyra, et al^{Reference Stopyra, Harper and Higgins26} evaluated the diagnostic accuracy of modified HEART score in which the H-E-A-R components of the score were collected by paramedics in the ambulance and the T (for troponin) was based on the initial contemporary troponin concentration from the ED. The primary outcome was the occurrence of major adverse cardiac events within 30 days.^{Reference Stopyra, Harper and Higgins26} In addition, van Dongen, et al^{Reference van Dongen, Tolsma and Fokkert27,Reference van Dongen, Fokkert and Tolsma28} have evaluated both the HEART and HEAR scores in the prehospital setting. The primary outcome for both papers was major adverse cardiac events within 35 days. Despite the great work to evaluate and validate the HEART, modified HEART, and HEAR scores in the prehospital setting, the sensitivity and NPV ranged from 78% to 95% and 92% to 97%, respectively. This introduces an unacceptable risk of missed diagnosis in the prehospital setting.

Another clinical decision rule, the History and ECG-Only Manchester Acute Coronary Syndromes (HE-MACS) decision aid, has been derived and validated in the ED environment based on variables that are obtainable in the prehospital setting. The HE-MACS uses that data to calculate the probability of ACS based on six variables. The algorithm then risk stratifies patients into four groups: “very low risk” (possible immediate rule out), “low risk,” “moderate risk,” and “high risk” (potentially rule in ACS).^{Reference Alghamdi, Howard and Reynard29} However, the accuracy this decision aid when used by paramedics in the prehospital environment has not yet been studied.