An accelerated diagnostic protocol in the emergency department identified a sizable group of symptomatic patients who were at low risk of having a short-term major cardiac event and who could be safely discharged, according to an observational study.

Assessment with a combination of Thrombolysis In Myocardial Infarction (TIMI) score, electrocardiogram, and baseline plus 2-hour troponin levels had a sensitivity of 99.7% (95% CI 98.1 to 99.9) and a specificity of 23.4% (95% CI 21.4 to 25.4) for identifying patients at low risk, according to Martin Than, MBBS, of the University of Otago in Christchurch, New Zealand, and colleagues.

In addition, the negative predictive value of the diagnostic protocol was 99.7% (95% CI 98.6 to 100) and the positive predictive value was 19% (95% CI 17.2 to 21), Than and colleagues reported in the June 5 Journal of the American College of Cardiology.

Chest pain represents the second most frequent complaint in the emergency department, and patients typically have an extensive work-up. This contributes to department overcrowding and possible adverse outcomes. Yet only 15% ultimately receive a diagnosis of acute coronary syndrome.

Because there is a need for a way of identifying patients at lowest risk who could be released quickly and followed closely on an outpatient basis, the researchers considered the suitability of a predefined rapid assessment protocol that required a TIMI risk score of zero, no new ischemic findings on ECG, and cardiac troponin (cTn) levels below the hospital’s established cutoff.

They enrolled 1,975 patients, most of whom were older white men. Many had risk factors such as a history of coronary artery disease, hypertension, and dyslipidemia.

During the 30 days after initial presentation, 15.3% of the cohort experienced an event such as acute myocardial infarction, cardiac arrest, serious ventricular arrhythmias, or death.

The risk stratification protocol used determined that 20% of patients were at low risk for an event, and only one of these patients actually experienced a major cardiac event during the month after evaluation, according to Than’s group.

This man had presented with chest pain, a normal ECG, and troponin levels below 0.01 µg/L at baseline, 0.03 µg/L 2 hours later, and 16.8 µg/L at 12 hours.

Angiography revealed stenosis of the right coronary and circumflex arteries; a stent was placed and the patient remained cardiac disease-free for the subsequent year.

The investigators also looked at the efficacy of the individual components for predicting an event, and found that TIMI score plus ECG findings alone missed five cases, while inclusion of baseline and 2-hour troponin concentrations identified four of these successfully.

A majority of the patients who were considered low risk did undergo further diagnostic evaluation - most commonly stress tests - during the subsequent month, with interventions in slightly more than 20%.

The investigators concluded that the risk for a short-term cardiac event in the identified low-risk group was 0.25%, and suggested that the use of sensitive troponin assays can eliminate the need for measuring other biomarkers such as creatine kinase and myoglobin.

They acknowledged certain limitations to the study, including its observational nature and the specificity of 23.5%, along with the use of the TIMI score, which was not developed for use in a low-risk population being assessed in the emergency department.

Nonetheless, they concluded that this approach could facilitate discharge for patients with little risk for serious adverse outcomes, and because the components are already in wide use, “rapid uptake of the [accelerated diagnostic protocol] is possible by most hospitals with the potential for immediate health service benefit.”

In an accompanying editorial comment, Eric P. Hess, MD, and Allan S. Jaffe, MD, from the Mayo Clinic in Rochester, Minn., argued that the proposed diagnostic protocol had “very significant limitations.”

“Specifically, 18% of [accelerated diagnostic protocol] negative patients underwent therapeutic and 2% underwent procedural interventions during their initial presentation or within 30 days of the [emergency department] visit, introducing the risk of outcome misclassification due to co-intervention,” Hess and Jaffe wrote.

In addition, the fact that three-quarters of the patients did have further diagnostic evaluations suggested that “further risk stratification after the visit was deemed essential in the majority,” they observed.

Hess and Jaffe also pointed out that other prediction models might be more suitable for use in emergency department evaluation of suspected acute coronary syndrome, such as the North American Chest Pain Rule and a score based on history, ECG, patient age, risk factors, and troponin concentrations.

And while emergency department resources continue to be greatly overstretched, and troponin assays may become increasingly sensitive, collaboration remains crucial for optimal care of these patients.

“Although we anticipate improvements in our ability to define a low-risk cohort and in metrics necessary to optimally use high sensitivity cTn assays, a multidisciplinary team approach with good follow-up is needed to provide consistent, high-quality health care for possible [acute coronary syndrome] patients in the context of an emergency care system at its breaking point,” Hess and Jaffe stated.

Primary source: Journal of the American College of Cardiology
Source reference: Than M, et al “2-hour accelerated diagnostic protocol to assess patients with chest pain symptoms using contemporary troponins as the only biomarker: the ADAPT trial” J Am Coll Cardiol 2012; 59: 2091-2098.

Additional source: Journal of the American College of Cardiology
Source reference: Hess E, Jaffe A “Evaluation of patients with possible cardiac chest pain: a way out of the jungle” J Am Coll Cardiol 2012; 59: 2099-2100.