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High-sensitivity troponin I test accelerates myocardial infarction triage

A high-sensitivity troponin I test showed great accuracy in ruling out myocardial infarction (MI) in patients with chest pain, with triage times reduced to 1 hour, and also showed better positive predictive ability than some other studies.

Presenting the data from the Biomarkers in Acute Cardiovascular Care (BACC) study at the European Society of Cardiology 2015 Congress, Dr Dirk Westermann (University Heart Centre Hamburg, Germany) concluded: “Use of this test in patients with suspected MI allows for highly accurate and rapid rule-out as well as rule-in, enabling safe discharge or rapid treatment initiation. “

“There are a lot of data now with these new high-sensitivity tests showing that 1 hour is enough. We don’t need to wait for 3 hours,” he stated.

“The Maraschino Cherry on Top of the Hot Fudge Sundae”

Designated discussant of the study, Dr Joseph Alpert (University of Arizona, Tucson), said: “This again supports the idea of discharging low-risk patients quickly and easily with these high-sensitivity troponin tests. They have very good negative predictive value. The BACC trial is the maraschino cherry on top of the hot fudge sundae in that it really establishes the usefulness of this strategy.”

He said the high-sensitivity troponin tests were now being used in many countries, but none had yet been approved in the US. “Unfortunately, we are one of the last places to have such tests. I hope this will be remedied soon.”

Alpert said other studies had shown similar ballpark benefits with high-sensitivity troponin tests, but the positive predictive value was better in this study than in earlier ones. He stressed, however, that there were many different high-sensitive troponin assays available, and each hospital has to think about which assay has the most appropriate cutoff values for their purposes.

Dr Gregg Stone (Columbia University, New York, NY) said the results would need to be validated in a US population before the test could be used there, and the data also needed to be evaluated in the context of symptoms.

Dr Kurt Huber (Wilhelminen Hospital, Vienna, Austria) described BACC as “one of the most important trials at this meeting.” He said: “Emergency departments are overcrowded. This trial suggests that about half of suspected NSTEMI patients can be rapidly diagnosed clearly, either ruling them in as having an MI or ruling them out as very low risk of cardiac disease. The other half have to wait for extra tests. This is not the only study to have shown this. But it is good confirmation of other studies.”

The main advantage of the new high-sensitivity tests is time, with triage decisions able to be made within 1 hour of presentation. If tests at both admission and 1 hour later are negative, patients can be safely discharged. This is a big improvement on the traditional troponin tests, which need to be repeated at 3 hours before a diagnosis can be made.

The new high-sensitivity tests also use much lower cutoff values for a positive result. The current trial used a cutoff value of 6 ng/L and a change of 12 ng/L between the two tests for a positive result, whereas traditional tests use a much higher level of about 27 ng/L (99th percentile of a healthy reference population).

The BACC study included 1045 patients (mean age 65 years) with acute chest pain suggestive of AMI presenting at the emergency room of the university hospital in Eppendorf, Hamburg, Germany.

Patients were assessed using both the standard 3-hour assay as well as a highly-sensitive 1-hour one.

Based on the standard approach, 184 patients were diagnosed with AMI and kept in the hospital, while the rest were discharged home. All patients were then followed for 6 months.

Comparing the results of both assays in the cohort, the researchers calculated the best troponin I cutoff value to rule out AMI was 6 ng/L—”far lower than the currently recommended 27 ng/L,” noted Westermann.

The algorithm was then validated in two independent cohorts (ADAPT and APACE trials) that included 4009 patients with acute chest pain suggestive of AMI. This showed a negative predictive value of 99.2% to 99.7% and a positive predictive value of 80.4% to 81.5%.

Westermann noted that based on the assay results, 41.2% of the cohort could be ruled out and discharged, while 11.9% were ruled in as having an MI. The other 46.9% of patients were known as the “gray zone” and needed further testing.

Fewer Deaths

Follow-up mortality at 6 months in the patients ruled out was 0.79% (three deaths) with the high-sensitive assay using the 6-ng/L cutoff vs 1.73% (12 deaths) using the 27-ng/L cutoff.

The researchers also validated the test in a general population of 75,000 individuals without known heart disease using data from the BiomarCare study. This showed that the 6-ng/L cutoff detected more cardiovascular deaths than the 27-ng/L-cutoff both at 1-year and 5-year follow-up.
Source: European Society of Cardiology (ESC) Congress 2015

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