Rapid MI Rule-Out Protocol Outperforms Older Assay

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Clinical judgment continues to be important when interpreting abnormal troponin values in patients presenting with symptoms warranting MI rule out.
Clinical judgment continues to be important when interpreting abnormal troponin values in patients presenting with symptoms warranting MI rule out.

A new protocol for rapid rule-out of myocardial infarction (MI) using a high-sensitivity troponin T (hs-CTnT) assay recently approved by the US Food and Drug Administration ruled out more patients and at a faster rate than the assay currently in use, according to a research letter published in Circulation.

The protocol was developed by a multidisciplinary team at Parkland Health and Hospital System in Dallas, Texas, using published data. A total of 536 patients (mean age, 55; 44% women) with symptoms that required MI rule-out (chest pain, shortness of breath, and other complaints) but no ST elevations on electrocardiography were evaluated. The patients were categorized into either “ruled out” or “abnormal,” based on hs-cTnT levels and change values.

Using the conventional assay, patients were classified as “ruled out” if their cTnT was <0.01 ng/mL at all time points or “abnormal” if any value was ≥ 0.01 ng/mL. In the study, 3 cardiologists adjudicated the final diagnosis and a second adjudication was conducted as a sensitivity analysis using the hs-cTnT assay instead of the conventional assay.

At 3 hours, 80.4% of patients were ruled out for MI vs 83.8% with the new hs-cTnT protocol. In addition, 30.0% were ruled out at baseline, 24.8% at 1 hour, and 28.9% at 3 hours. According to the new protocol, 16.2% of patients were considered abnormal vs 19.6% with the conventional assay (P =.03). The new protocol had a positive predictive value of 13% for a final adjudicated MI diagnosis, sensitivity and negativity predictive values of 100%, and a specificity of 86%.

There were no recurrent MI events during 30 days of follow-up in the patients who were ruled out. In addition, a higher percentage of patients were ruled out with the new algorithm compared with the European Society of Cardiology 0/1 hour algorithm (83.8% vs 55.4%; P <.0001), which meant that 152 of 154 patients were moved from observation status to the rule-out group.

“A subtle but important distinction of our protocol from the [European Society of Cardiology] 0/1 protocol is the classification of individuals as ‘abnormal' rather than ‘rule-in,' the investigators noted. “We recommend a similar approach in other centers with an anticipated low MI prevalence among those undergoing troponin measurement.”

The researchers concluded that clinical judgment is still of the utmost importance when interpreting abnormal troponin values as the hs-cTnT assay is implemented in the United States, “where troponin is measured more indiscriminately than in many other countries.”

In an email interview with Cardiology Advisor, coauthor, Rebecca Vigen, MD, MSCS, noted, "This [protocol] may allow many patients to be reassured sooner that their symptoms are not due to a heart attack and doctors to more quickly begin looking for other causes of their symptoms."

Disclosures: Dr Dierks reports consulting fees from Roche Diagnostics and Siemens Diagnostics. Dr de Lemos reports grant support from Roche Diagnostics and Abbott Diagnostics and consulting fees from Roche Diagnostics, Abbott Diagnostics, and Ortho Clinical Diagnostics. Dr Das reports consulting fees from Roche Diagnostics.

Reference

Vigen R, Kutscher P, Fernandez F, et al. Evaluation of a novel rule-out myocardial infarction protocol incorporating high-sensitivity troponin T in a US hospital [published online August 6, 2018]. Circulation. doi:10.1161/CIRCULATIONAHA.118.033861

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