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Source: Thailand Medical News  Jan 08, 2020  4 years, 10 months, 2 weeks, 19 hours, 17 minutes ago

Using Troponin Levels To Rule Out Ischemia Is Not Reliable

Using Troponin Levels To Rule Out Ischemia Is Not Reliable
Source: Thailand Medical News  Jan 08, 2020  4 years, 10 months, 2 weeks, 19 hours, 17 minutes ago
According to a new Swiss study published in the Annals of Internal Medicine, even very low concentrations of high-sensitivity cardiac troponin I (hs-cTnI) cannot safely rule out inducible myocardial ischemia in patients with symptomatic coronary artery disease (CAD).


 
Typically, troponins are proteins found in the cardiac and skeletal muscles. When the heart is damaged, it releases troponin into the bloodstream. Doctors measure your troponin levels to detect whether or not you’re experiencing a heart attack. This test can also help doctors find the best treatment sooner.
 
In the past, doctors used other blood tests to detect a heart attack. This wasn’t effective, however, because the tests weren’t sensitive enough to detect every attack. They also involved substances that weren’t specific enough to the heart muscle. Smaller heart attacks left no trace on blood tests.

Troponin is more sensitive. Measuring cardiac troponin levels in the blood allows doctors to diagnose a heart attack or other heart-related conditions more effectively, and provide immediate treatment.
 
Troponin proteins are split into three subunits: troponin C (TnC), troponin T (TnT) and troponin I (TnI)
 
However findings from this new study questions the reliability of using troponin levels to rule out ischemia.
 
Dr Joan Walter, M.D., Ph.D., from University Hospital Basel in Switzerland, and colleagues measured circulating hs-cTn concentrations among 1,896 consecutive patients with coronary artery disease referred with symptoms possibly related to inducible myocardial ischemia. Providers were blinded to results from tests used to adjudicate the presence of inducible myocardial ischemia, including myocardial perfusion imaging with single-photon emission computed tomography and, when available, coronary angiography and fractional flow reserve measurements.
 
The medical researchers found that 46 percent of patients had inducible myocardial ischemia. A cutoff value of 2.5 ng/L for hs-cTnI provided a negative predictive value (NPV) of 70 percent and a sensitivity of 90 percent for exclusion of inducible myocardial ischemia. There was no hs-cTnI cutoff that reached both predefined performance characteristic targets. With alternative assays (hs-cTnI or hs-cTnT), there was no cut off that achieved the target performance: hs-cTnT concentrations <5 ng/L yielded an NPV of 66 percent, and hs-cTnI concentrations <2 ng/L yielded an NPV of 68 percent.
 
Dr Walter told Thailand Medical News via a phone interview, "In conclusion, in symptomatic patients with coronary artery disease, very low hs-cTn concentrations, including hs-cTnI-Architect concentrations below 2.5 ng/L, do not generally allow users to safely exclude inducible myocardial ischemia."
 
Several authors report financial ties to Abbott, Roche, Schiller, and Singulex, all of which provided funding for the study.
 
Reference: Walter J, du Fay de Lavallaz J, Koechlin L, et al. Using High-Sensitivity Cardiac Troponin for the Exclusion of Inducible Myocardial Ischemia in Symptomatic Patients: A Cohort Study. Ann Intern Med. 2020;  doi: https://doi.org/10.7326/M19-0080

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