Pre-implementation evaluation of a rule out MI protocol incorporating high sensitivity troponin T in a United States hospital

From the 2018 HVPAA National Conference

Rebecca Vigen (University of Texas Southwestern Medical Center), Patricia Kutscher (Parkland Health and Hospital System), Fernabelle Fernandez (Parkland Health and Hospital System), Amy Yu (Parkland Health and Hospital System), Bryan Bertulfo (Parkland Health and Hospital System), Ibrahim Hashim (University of Texas Southwestern Medical Center), Deborah Diercks (University of Texas Southwestern Medical Center), James De Lemos (University of Texas Southwestern Medical Center), Sandeep Das(University of Texas Southwestern Medical Center)

Background

The U.S. FDA approved the high-sensitivity troponin T (hs-cTnT) assay in January 2017. Rapid myocardial infarction (MI) rule out protocols capitalizing on its greater sensitivity and precision may alleviate emergency department crowding in U.S. hospitals; hs-cTnT has been validated in non-U.S. settings where MI prevalence among those tested is higher.

Objectives

To evaluate the safety and effectiveness of a rapid MI rule out algorithm using hs-cTnT in U.S. practice.

Methods

A multidisciplinary team at Parkland Health and Hospital System (PHHS), drawn from cardiology, clinical laboratory, emergency medicine, and hospital medicine, developed a novel hs-cTnT protocol (Supplemental figure 1). Prior to implementation, an observational study was performed to evaluate safety and potential impact compared with existing practice using the conventional cTnT assay.  Both cTnT and hs-cTnT were measured at 0, 1, and 3 hours after presentation in 536 patients who presented to the PHHS emergency department with possible acute MI between August and October of 2017.  Individuals were classified as “ruled out” or “abnormal” based on the hs-cTnT protocol. Individuals were classified as ruled out with the conventional assay if cTnT was < 0.01 ng/mL at all time points and abnormal if any value was > 0.01 ng/mL. The final diagnosis was adjudicated by a panel of three cardiologists. MI was classified using the Third Universal Definition of MI.

Results

Of the 536 patients, 56% were men and 44% were women with a mean age of 55 years.  The final adjudicated diagnosis was AMI in 2.1%, unstable angina in 0.4%, nonischemic myocardial injury in 17.0%, and no evidence of AMI, cardiac injury or unstable angina in 80.2%.  At three hours, 80.4% of patients ruled out for AMI with the conventional assay vs. 83.8% with the new hs-cTnT protocol (p=0.03), including 30.0% at baseline, 24.8% at 1 hour, and 28.9% at 3 hours (Supplemental figure 2). The new protocol had a sensitivity and NPV of 100%, specificity of 86%, and positive predictive value of 12.6% for a final adjudicated diagnosis of MI.

Conclusion

This new protocol for rapid rule out of AMI using the hs-cTnT assay, applied to a contemporary U.S. emergency department population, ruled out more patients than the existing protocol using the conventional cTnT assay; half of all patients ruled out for AMI by one hour after presentation. This protocol appears safe, with a sensitivity and negative predictive value of 100%.  The positive predictive value of an abnormal hs-cTnT value was low, reflecting the fact that troponin is measured more indiscriminately in the U.S. than in many other countries and highlighting that clinical judgement remains essential in the interpretation of abnormal hs-cTnT. A subtle but important distinction of our protocol is the classification of individuals as “abnormal” rather than “rule in”.

Implications for the Patient

This protocol offers a pathway for other health care systems in the United States on how to incorporate the hs-cTnT assay into practice. Future studies are needed to evaluate secondary testing strategies after rule out and to optimize the resource implications of this novel protocol.

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