Use of high-sensitivity cardiac troponin I (hs-cTnI) assay might allow cardiac stress tests to be avoided in some patients, reducing health care costs and radiation exposure, according to an observational study.
Researchers used data from two previous studies of patients with stable coronary artery disease (CAD) who underwent either treadmill or pharmacologic stress testing and had presence of inducible myocardial ischemia determined by myocardial perfusion imaging with technetium-99m single-photon emission CT. Their resting plasma hs-cTnI was measured within one week of the stress test. Results of the study were published Nov. 6 by Annals of Internal Medicine.
The derivation cohort included 589 patients with detectable hs-cTnI levels, ranging from 1.3 to 377.9 pg/mL (median value, 4.3 pg/mL). The researchers calculated the specificity, sensitivity, negative predictive value (NPV), and positive predictive value (PPV) of hs-cTnI levels between 1.5 pg/mL and 3.0 pg/mL for identifying inducible myocardial ischemia and found that a cutoff of 2.5 pg/mL had the highest NPV. Of the 101 patients with an hscTnI level below 2.5 pg/mL, only 10 had inducible myocardial ischemia (NPV, 90%; 95% CI, 83% to 95%) and three had inducible ischemia involving at least 10% of the myocardium (NPV, 97%; 95% CI, 92% to 99%).
The study also included a 118-patient validation cohort, in which the median hs-cTnI level was 4.8 pg/mL. Thirty-two patients had an hs-cTnI level below 2.5 pg/mL, four of whom had inducible ischemia (NPV, 88%; 95% CI, 71% to 96%) and two of whom had ischemia of 10% or greater (NPV, 94%; 95% CI, 79% to 99%).
After a median follow-up of three years in the derivation cohort, no adverse events occurred in patients with an hs-cTnI level below 2.5 pg/mL, compared with 33 (7%) cardiovascular deaths or incident myocardial infarctions among those with an hs-cTnI level of 2.5 pg/mL or greater.
The authors concluded that very low hs-cTnI levels may be useful in excluding inducible myocardial ischemia in patients with stable CAD. They cautioned that the results may not be applicable to patients with unstable angina or without known CAD, but they noted that intermittent stress testing is performed routinely in patients with stable CAD, and thus triage with hs-cTnI could likely reduce the number of stress tests performed.
An accompanying editorial called the results of this, and previous similar studies, encouraging. “Taken together, these data suggest that hs-cTn assays may be more accurate, convenient, quick, and cost-effective than MPS [myocardial perfusion single-photon emission computed tomography] in predicting the course of stable CAD,” the editorial said.