High-sensitivity cardiac troponin I (hs-cTnI) levels below 2.5 ng/L identify patients with coronary artery disease who have a very low risk for myocardial ischemia during stress testing and a low medium-term risk for adverse cardiovascular events.
A North American study, published in the Annals of Internal Medicine, suggested the findings could be used to risk-stratify patients and reduce unnecessary stress testing in the low risk group.
The study followed two cohorts of patients with largely asymptomatic and stable CAD for a median of three years.
Patients in both groups with inducible myocardial ischemia had higher hs-cTnI levels than those without ischemia on exercise or pharmacologic stress testing.
In the larger cohort of 589 patients, a hs-cTnI <2.5 ng/L (or pg/mL) had the best negative predictive value for inducible myocardial ischemia while meeting a minimum sensitivity threshold of 90% or greater.
During follow-up, no patients with an hs-cTnI level below the cut-off and 33 (7%) above the cut-off had a cardiovascular death or myocardial infarction.
A smaller cohort of 118 patients validated the cut-off point.
“Of 28 participants with an hs-cTnI level below 2.5 pg/mL and no resting perfusion defect, only 1 had inducible ischemia and none had ischemia of 10% or greater,” the study said.
“Thus, on the basis of the CIs of our estimates, this cutoff value ruled out inducible myocardial ischemia in at least 71% to 83% of patients and ischemic defect of 10% or greater in 79% to 92% of patients. To our knowledge, this is the first study in patients with known, stable CAD to show that an hs-cTnI cutoff below 2.5 pg/mL identifies those who are very unlikely to develop myocardial ischemia and who have no risk for adverse cardiovascular outcomes during medium-term follow-up.”
The study found a hs-cTnI level below 2.5 pg/mL was present in 17% and 27% of the derivation and validation cohorts respectively.
An accompanying editorial in the journal said the study was ‘an important contribution to the area of prognostication in patients with stable CAD’.
“Exploring hs-cTnl values from 1.5 to 3.0 pg/ml in increments of 0.1 pg/ml, the authors determined that an hs-cTnl below 2.5 pg/mL fulfilled their a priori requirement for a negative predictive value greater than 90% and a sensitivity greater than 90% for myocardial ischemia on myocardial perfusion single-photon emission on CT (MPS).”
“This hs-cTnl threshold also had a negative predictive value of 97% in the derivation cohort and 94% in the validation cohort for ischemia involving 10% or more of the myocardium.”
The editorial concluded hs-cTn assays may be ‘more accurate, convenient, quick and cost effective’ than MPS in predicting the course of stable CAD.