Conference Coverage

Novel cardiac troponin protocol rapidly rules out MI



– An accelerated rule-out pathway, reliant upon a single high-sensitivity cardiac troponin test upon presentation to the ED with suspected acute coronary syndrome, reduced length of stay and hospital admission rates without increasing cardiac events at 30 days or 1 year in a major Scottish study.

“We conclude that implementation of this early rule-out pathway is both effective and safe, and adoption of this pathway will have major benefits for patients and health care systems,” Nicholas L. Mills, MBChB, PhD, said in presenting the results of the HiSTORIC (High-Sensitivity Cardiac Troponin at Presentation to Rule Out Myocardial Infarction) trial at the annual congress of the European Society of Cardiology.

Indeed, in the Unites States, where more than 20 million people per year present to EDs with suspected ACS, the 3.3-hour reduction in length of stay achieved in the HiSTORIC trial by implementing the accelerated rule-out pathway would add up to a $3.6 billion annual savings in bed occupancy alone, according to Dr. Mills, who is chair of cardiology at the University of Edinburgh.

The HiSTORIC pathway incorporates separate thresholds for risk stratification and diagnosis. This strategy is based on an accumulation of persuasive evidence that the major advantage of high-sensitivity cardiac troponin testing is to rule out MI, rather than to rule it in, Dr. Mills explained.

HiSTORIC was a 2-year, prospective, stepped-wedge, cluster-randomized, controlled trial including 31,492 consecutive patients with suspected ACS who presented to seven participating hospitals in Scotland. Patients were randomized, at the hospital level, to one of two management pathways. The control group got a standard guideline-recommended strategy involving high-sensitivity cardiac troponin I testing upon presentation and again 6-12 hours later, with MI being ruled out if the troponin levels were not above the 99th percentile.

In contrast, the novel early rule-out strategy worked as follows: If the patient presented with at least 2 hours of symptoms and the initial troponin I level was below 5 ng/L, then MI was ruled out and the patient was triaged straightaway for outpatient management. If the level was above the 99th percentile, the patient was admitted for serial testing to be done 6-12 hours after symptom onset. And for an intermediate test result – that is, a troponin level between 5 ng/L and the 99th percentile – patients remained in the ED for retesting 3 hours from the time of presentation, and were subsequently admitted only if their troponin level was rising.

Using the accelerated rule-out strategy, two-thirds of patients were quickly discharged from the ED on the basis of a troponin level below 5 ng/mL, and another 7% were ruled out for MI and discharged from the ED after a 3-hour stay on the basis of their second test.

The primary efficacy outcome was length of stay from initial presentation to the ED to discharge. The duration was 10.1 hours with the guideline-recommended pathway and 6.8 hours with the accelerated rule-out pathway, for a statistically significant and clinically meaningful 3.3-hour difference. Moreover, the proportion of patients discharged directly from the ED without hospital admission increased from 53% to 74%, a 57% jump.

The primary safety outcome was the rate of MI or cardiac death post discharge. The rates at 30 days and 1 year were 0.4% and 2.6%, respectively, in the standard-pathway group, compared with 0.3% and 1.8% with the early rule-out pathway. Those between-group differences favoring the accelerated rule-out pathway weren’t statistically significant, but they provided reassurance that the novel pathway was safe.

Of note, this was the first-ever randomized trial to evaluate the safety and efficacy of an early rule-out pathway. Other rapid diagnostic pathways are largely based on observational experience and expert opinion, Dr. Mills said.

The assay utilized in the HiSTORIC trial was the Abbott Diagnostics Architect high sensitivity assay. The 5-ng/L threshold for early rule-out was chosen for the trial because an earlier study by Dr. Mills and coinvestigators showed that a level below that cutoff had a 99.6% negative predictive value for MI (Lancet. 2015 Dec 19;386[10012]:2481-8)

The early rule-out pathway was deliberately designed to be simple and pragmatic, according to the cardiologist. “One of the most remarkable observations in this trial was the adherence to the pathway. We prespecified three criteria to evaluate this and demonstrated adherence rates of 86%-92% for each of these criteria. This was despite the pathway being implemented in all consecutive patients at seven different hospitals and used by many hundreds of different clinicians.”

Discussant Hugo A. Katus, MD, called the HiSTORIC study “a really urgently needed and very well-conducted trial.”

Dr. Hugo Katus, head of the department of cardiovascular medicine at Heidelberg (Germany) University Bruce Jancin/MDedge News

Dr. Hugo Katus

“There were very consistently low MI and cardiac death rates at 30 days and 1 year. So this really works,” commented Dr. Katus, who is chief of internal medicine and director of the department of cardiovascular medicine at Heidelberg (Germany) University.

“Accelerated rule-out high-sensitivity cardiac troponin protocols are here to stay,” he declared.

However, Dr. Katus voiced a concern: “By early discharge as rule out, are other life-threatening conditions ignored?”

He raised this issue because of what he views as the substantial 1-year all-cause mortality and return-to-hospital rates of 5.8% and 39.2% in the standard-pathway group and 5.2% and 38.9% in the accelerated rule-out patients in HiSTORIC. An accelerated rule-out strategy should not prohibit a careful clinical work-up, he emphasized.

Dr. Mills discussed the results in a video interview.

The HiSTORIC trial was funded by the British Heart Foundation. Dr. Mills reported receiving research grants from Abbott Diagnostics and Siemens.

Simultaneous with Dr. Mills’ presentation of the HiSTORIC trial results at the ESC congress, an earlier study that formed the scientific basis for the investigators’ decision to employ distinct risk stratification and diagnostic thresholds for cardiac troponin testing was published online (Circulation. 2019 Sep 1. doi: 10.1161/CIRCULATIONAHA.119.042866). The actual HiSTORIC trial results will be published later.

Dr. Katus reported holding a patent for a cardiac troponin T test and serving as a consultant to AstraZeneca, Bayer, Boehringer Ingelheim, and Novo Nordisk.

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