Abstract 979: Novel Nanoparticle Cardiac Troponin I Assay Detects Myocardial Injury in Most Patients with Unstable Angina: Observations from the PROTECT-TIMI 30 Trial
At least one third of patients with non-ST elevation acute coronary syndrome present with no evidence of myonecrosis using current generation assays for cardiac troponin I (cTnI). Interest in developing biomarkers to facilitate diagnosis in such patients with unstable angina (UA) remains intense. We investigated the clinical sensitivity of a new ultra-sensitive nanoparticle cTnI assay (Nanosphere, Inc) in a cohort who presented with non-ST elevation acute coronary syndrome. A positive cTnI was defined as >=0.10 ng/ml based on our prior work with a current generation cTnI assay and >=0.002 ng/ml (99%ile) for the nano-cTnI assay. In 50 patients with UA (serial negative current generation cTnI to 24 hrs), 54%, 78% and 90% had elevated levels at 0, 2 and 8 hrs with the nano-cTnI (Figure⇓, Left; p<0.001 compared with current generation cTnI). In 50 patients with definite NSTEMI but an initial negative result with the current generation cTnI, 86% and 100% had a detectable nano-cTnI at 0 hrs and 2 hrs (Figure⇓, Right; p<0.001 compared with current generation cTnI). No UA or NSTEMI pts had a positive current generation TnI without a measurable nano-cTnI. Additional analysis using the lower limit of detection for the current generation cTnI (0.04 ng/ml) found elevation of standard cTnI in only 24% of the UA cohort at 24 hr. Using a new nanoparticle assay for cTnI, myocardial injury is detectable in the majority of patients presently classified as having UA, suggesting that ischemic chest pain at rest without myocardial injury is rare. It will be important to assess the prognostic significance of cTnI concentrations below the level measured by standard assays.