Detection of myocardial injury in patients with unstable angina using a novel nanoparticle cardiac troponin I assay: Observations from the PROTECT-TIMI 30 Trial
Received 24 November 2008; accepted 5 June 2009. published online 16 July 2009.
Background
At least 30% of patients with non–ST-elevation acute coronary syndrome present without evidence of myonecrosis using current generation troponin assays. A new generation of research assays for troponin that offer a >10-fold increase in analytical sensitivity has emerged.
Methods
To perform a pilot study to evaluate the clinical sensitivity of a new ultra-sensitive nanoparticle assay for cardiac troponin I (nano-cTnI), we identified 50 patients with unstable angina (serial negative cTnI) and 50 patients with non–ST-elevation myocardial infarction with an initially negative current generation cTnI result. We measured cTnI using an assay (Nanosphere, Northbrook, IL) that can detect pg/mL concentrations of cTnI (detection-limit 0.0002 μg/L).
Results
Measured at 0, 2, and 8 hours with the nano-cTnI assay 44%, 62%, and 82% of patients with unstable angina defined by the current-generation assay had an elevated nano-cTnI result (≥0.003 μg/L, 99th percentile decision-limit, coefficient of variation <10%). In patients with definite myocardial injury (current-generation cTnI ≥0.1 μg/L) but an initially negative cTnI, 72% and 98% had a nano-cTnI ≥0.003 μg/L at 0 and 2 hours. No patient had a positive current-generation cTnI without an elevated nano-cTnI level.
Conclusions
In this pilot study using a nanoparticle assay for cTnI, myocardial injury was detectable in a substantial proportion of patients presently classified as having unstable angina, suggesting that ischemia with rest pain without injury is rare. The emergence of a new generation of troponin assays has the potential to lead to new clinical applications based on enhanced analytical performance at very low concentrations of troponin.
aTIMI Study Group, Brigham and Women's Hospital and Department of Medicine, Boston, MA
bCardiovascular Division, Brigham and Women's Hospital and Department of Medicine, Boston, MA
Reprint requests: David A. Morrow, MD, MPH, TIMI Study Group/Cardiovascular Division Brigham and Women's Hospital 75 Francis Street Boston, MA 02115.
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