A more sensitive test for heart attack may cut the diagnosis time to one hour, removing the need for prolonged monitoring in 3 out of 4 patients who present to the Emergency Department (ED) with chest pains, according to a new US study published this week.

Writing about their work in a paper published online on 13 August in the Archives of Internal Medicine, the researchers suggest the test, which screens more sensitively for changes in a standard biochemical marker for myocardial infarction (heart attack), may help move patients more quickly through the ED, thus reducing congestion and saving time and money.

Around 10% of all emergency department consultation in the US are people with symptoms that might suggest acute myocardial infarction (AMI).

The Need for a Rapid Test

In an accompanying commentary, L. Kristin Newby, professor of medicine at Duke University Medical Center in North Carolina, explains there is a demand for new tools that can help rapid triage of patients with suspected heart attack, especially as EDs are getting more and more crowded.

When a patient presents to the ED with chest pains, the first thing doctors do is rule in or rule out for heart attack. The cornerstone for diagnosing the condition relies on clinical assessment, electrocardiography and measurement of a biochemical marker called cardiac troponin (or cTn). Without a rapid test for the marker, it can take 3 hours or more to check for increases in levels.

In their introduction, first author Tobias Reichlin, of University Hospital Basel, Switzerland, and colleagues, explain while there is evidence that high-sensitivity cardiac troponin (hs-cTn) assays appear to improve the early diagnosis of AMI, it is not clear how doctors should use them in practice, especially as there is a suggestion they may also increase positive results for other conditions.

So they developed and validated an algorithm designed to help doctors rapidly rule in and rule out AMI.

The Study

For their multicenter study Reichlin and colleagues recruited 872 patients who presented to the ED with acute chest pain. AMI was the final diagnosis in 147 (17%) of them.

They developed the algorithm in half of the patients and validated it in the remaining half. The algorithm used baseline hs-cTnT and absolute changes in levels of the biochemical marker within the first hour.

When they validated the test in the second group of patients, within one hour it classed 60% (259 patients) of them as rule-out, 17% (76) as rule-in, and 23% (101) as being in the observational zone.

They found the cumulative 30-day survival was nearly 100%, 98.6% and 95.3% for patients classed as rule-out, observational zone, and rule-in respectively. Reichlin and colleagues conclude:

"Using a simple algorithm incorporating hs-cTnT baseline values and absolute changes within the first hour allowed a safe rule-out as well as an accurate rule-in of AMI within 1 hour in 77% of unselected patients with acute chest pain."

"This novel strategy may obviate the need for prolonged monitoring and serial blood sampling in 3 of 4 patients," they add.

Comment on the Study

Newby writes that the study is an important step forward in the use of hsTn (high-sensitivity troponin) as a triage tool for ED patients with a possible heart attack, but there is still a lot of work to be done before there is sufficient evidence that hsTn and the algorithms Reichlin and colleagues have developed can be used in clinical practice.

She also points to a practical problem which is far from "simple" as the authors describe. And that is in practice, doctors would need different groups of algorithms for different groups of patients (for instance depending on age and other characteristics).

This added consideration will "challenge application by busy clinicians unlikely to remember or accurately process the proposed algorithm", says Newby.

Because of this, she suggests if the hsTn algorithms are validated, then they should form part of electronic health records so doctors have all the information, with interpretation and explanation of the algorithm to hand when conducting triage and treatment.

Research grants from the Swiss National Science Foundation, the Swiss Heart Foundation, Abbott, Roche, Siemens and the Department of Internal Medicine, University Hospital Basel, financed the study. Roche also donated the blood assay the researchers used.

Written by Catharine Paddock PhD