Biomarkers ousting imaging modalities? Not so fast

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 - Chest pain, angina

A single resting high-sensitivity troponin T (hsTnT) measurement may predict abnormal myocardial perfusion imaging (MPI), independent of cardiovascular risk factors and time of presentation in patients with acute chest pain, according to a study published in this month's Journal of the American College of Cardiology: Cardiovascular Imaging. The authors trumpeted hsTnT as a potentially “powerful triage tool” for emergency departments (EDs) but editorialists argued otherwise.

Waleed Ahmed, MD, of the radiology department of Massachusetts General Hospital in Boston, and colleagues used a subset of patients from the observational cohort study, ROMICAT I (Rule Out MI Using Computer-Assisted Tomography). ROMICAT had enrolled consecutive adult patients with a low-to-intermediate likelihood of acute coronary syndrome (ACS) who presented to the hospital’s ED over an 18 month period with acute chest pain and whose initial electrocardiogram (ECG) and biomarkers were not indicative of a high likelihood for ACS. The patients’ care during index hospitalization included serial ECGs, biomarkers and stress test or cardiac catheterization as determined by a physician.

For their study, Ahmed et al identified 138 patients who underwent clinically indicated rest and stress SPECT-MPI and 64-slice CT angiography and who had an hsTnT measurement. Patients with MI during index hospitalization were excluded. They assessed hsTnT to determine its diagnostic value for detecting abnormal rest stress SPECT-MPI and coronary artery disease (CAD) without objective evidence for ACS.

Patients in the study had a mean age of 54 years, 46 percent were men and 13.7 percent had abnormal SPECT-MPI. They found that median hsTnT levels were twice as high in patients with abnormal SPECT-MPI compared with those with normal SPECT-MPI, at 9.41 pg/ml vs. 4.89 pg/ml. The odds of having an abnormal SPECT-MPI increased two-fold for every doubling of hsTnT levels, which the researchers wrote showed good discriminatory value.

According to their analysis, hsTnT levels as low as 5.73 and 4.26 pg/ml had sensitivity of 80 percent and 90 percent, respectively; specificity of 62 percent and 46 percent, and negative predictive value of 96 percent and 96 percent. Reversible MI and the extent of coronary atherosclerosis independently and incrementally predicted the measured hsTnT levels. Based on the results, early resting hsTnT might serve as a “powerful triage tool,” they proposed.

“Overall, our findings suggest that early resting hsTnT may improve the effectiveness of the management of patients with acute chest pain and low-to-intermediate risk for ACS,” Ahmed et al wrote. “Given the low prevalence of abnormal SPECT-MPI and ACS in this population and the risks and costs associated with diagnostic testing, early hsTnT testing may eliminate the need for imaging in a substantial number of patients who currently undergo one or more diagnostic imaging tests.”

Todd D. Miller, MD, and Kent R. Bailey, PhD, both of the Mayo Clinic in Rochester, Minn., offered a litany of limitations in an accompanying editorial. They noted, among other issues, that the study was small with a low-risk patient population that might not be generalizable to other emergency room patient populations; Ahmed et al used a single time point for measuring hsTnT and not serial measurements; and attenuation correction was not applied for SPECT imaging although the patient population had a mean body mass index of 30.

They described the study as “an important first step for evaluating hsTnT against conventional imaging modalities commonly applied in the ED” but contended that more robust data were needed.