More MI rule-outs than earlier test or European protocol in U.S. study
A new protocol for high-sensitivity cardiac troponin T (hs-cTnT) safely ruled out MI faster and for more patients presenting to a U.S. emergency department with chest symptoms but no ST elevations on ECG, according to an observational study.
Whereas the conventional fourth-generation cTnT assay ruled out MI for 80.4% of patients at 3 hours, the new protocol ruled out 83.8% by the same point (30.0% at baseline, 24.8% at 1 hour, and 28.9% at 3 hours), reported the group led by Rebecca Vigen, MD, of University of Texas Southwestern Medical Center in Dallas.
That left 19.6% and 16.2% of patients with abnormal results for each respective test (P=0.03), the authors showed in a research letter published online in Circulation.
The hs-cTnT-based protocol had more patients ruled out than the European Society of Cardiology (ESC)'s 0/1 hour algorithm (83.8% versus 55.4%, P<0.0001). No patient who was ruled out had recurrent MI events over the next 30 days of follow-up.
"In summary, a new protocol for rapid rule-out of MI 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 assay, and did so sooner, with more than half of all patients ruled out by 1 hour after presentation," Vigen and colleagues said.
Where the new protocol differs from previous ones is the addition of a 3-hour hs-cTnT measurement for patients classified into the indeterminate zone at 1 hour. Additionally, patients are categorized as "abnormal" rather than having MI "ruled in," unlike the ESC algorithm.
The new hs-cTnT protocol had sensitivity and negative predictive value of 100% and specificity of 86%.
The positive predictive value of 13% for a final diagnosis of MI as adjudicated by three cardiologists was low, investigators acknowledged. "Thus, clinical judgment remains essential in the interpretation of abnormal troponin values as the hs-cTnT assay becomes adopted in the United States, where troponin is measured more indiscriminately than in many other countries."
Vigen and colleagues evaluated the protocol, developed at Parkland Health and Hospital System in Dallas, in their study of 536 patients (mean age 55 years, 44% women) presenting to the emergency department in 2017 with chest pain, shortness of breath, or other symptoms warranting MI rule-out but no ST elevations on ECG. A final adjudicated diagnosis of MI was assigned to 2.1%.
"We recommend a similar approach in other centers with an anticipated low MI prevalence among those undergoing troponin measurement," they said, provided that future studies give external validation to the novel algorithm and determine what it will cost in resources.
Vigen was supported by an award from the National Center for Advancing Translational Sciences of the NIH.
Co-authors reported relevant ties to industry.
Source Reference: Vigen R, et al "Evaluation of a novel rule-out myocardial infarction protocol incorporating high-sensitivity troponin T in a US hospital" Circulation 2018; DOI: 10.1161/CIRCULATIONAHA.118.033861.
Read the original article on Medpage Today: New hs-cTnT Algorithm Wins With Pathway for Intermediate Results