Abstract 3108: Single Molecule Troponin Detection to Assess for Transient Myocardial Ischemia

Abstract

Background : It has been proposed that small amounts of cardiac troponin (Tn) may be released from myocytes in the setting of reversible myocardial injury. We hypothesized that a more sensitive Tn assay could permit the quantification of transient myocardial ischemia. Methods : Blood samples were obtained before and 4 hrs after stress testing with perfusion imaging in 99 pts w/o recent angina. Tn was measured using the current generation TnT assay (Roche, limit of detection, LOD, 0.01 ng/ml) and the new Singulex TnI assay, which, using single molecule counting technology, has a LOD 50 fold lower (0.2 pg/ml). Pts were categorized by severity of ischemia on perfusion imaging; median changes in Tn levels were compared across ischemic groups. Results : Using the Singulex assay, TnI was detectable in all pts before stress testing (median 4.4 pg/ml). The median duration of angina during testing was 0, 0, and 3 mins in pts with none, mild, and mod/sev ischemia. By 4 hrs, TnI levels were unchanged in pts w/o ischemia, whereas circulating levels had significantly increased by 1.37 pg/ml (24%) in pts with mild ischemia (P=.002) and by 2.08 pg/ml (40%) in pts with mod/sev ischemia (P=.0006) (Fig ). In a multivariable model that included mins of exercise, angina, and ST changes, change in TnI was a significant predictor of ischemia (OR 3.36, P=.03). In contrast, using the existing TnT assay there were no detectable differences in Tn levels (median difference 0.00 ng/ml in all groups). Conclusion : A 50-fold more sensitive troponin assay can quantify rises in circulating troponin in patients experiencing brief, provoked myocardial ischemia. The clinical applications of such assays warrant further study.