Incidence and Outcomes of Unstable Angina in Patients with Low High-Sensitivity Cardiac Troponin I Values—A Substudy of the RACE-IT Trial

Abstract Background Unstable angina has become an exceedingly rare diagnosis in the era of high-sensitivity cardiac troponin (hs-cTn). We sought to identify the incidence of unstable angina and characterize patients with low hs-cTn in Emergency Departments (EDs). Methods A prespecified secondary analysis of the R apid A cute C oronary Syndrome E xclusion using high-sensitivity I cardiac T roponin (RACE-IT) trial was conducted. RACE-IT was a stepped-wedge randomized trial comparing two rule-out protocols (0/1- and 0/3-hour) for myocardial infarction (MI) in nine EDs from July 2020 to April 2021. All patients had hs-cTnI (Beckman Coulter) concentrations below or equal to the 99 th percentile upper reference limit of 18 ng/L. The primary outcome was unstable angina, based on the ISCHEMIA trial definition, which required electrocardiographic changes or findings at coronary angiography (angiographic evidence of plaque rupture or thrombus). Results Of the 32,608 patients in the trial, 60 patients (0.2%) met the definition of unstable angina of which 46 (77%) had obstructive disease at coronary angiography and 17 (28%) had an ischemic electrocardiogram. Coronary revascularization was performed in 45 (75%) patients and 7 (12%) had left main or 3-vessel coronary artery disease. There were 7 (12%) patients with non-obstructive coronary artery disease, and 7 (12%) who had angiographically unremarkable coronary arteries. Patients with unstable angina were older (p=0.032), more likely to be male (p=0.012), with a higher prevalence of hypertension (p