Incidence and outcomes of unstable angina in patients with low high-sensitivity cardiac troponin I values -- A substudy of the RACE-IT trial

BackgroundUnstable 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). MethodsA prespecified secondary analysis of the Rapid Acute Coronary Syndrome Exclusion using high-sensitivity I cardiac Troponin (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 99th 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). ResultsOf 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<0.001), known coronary artery disease (p<0.001), peripheral vascular disease (p=0.030), and a higher serum creatinine (p=0.043). At 30 days, two patients had a type 1 MI and there were no deaths. ConclusionUnstable angina was diagnosed in 1 in 500 patients with a low hs-cTnI value at presentation to the ED and these patients have an excellent prognosis at 30 days. These patients tend to not have high-risk anatomy and 1 in 4 have non-obstructive coronary artery disease or angiographically unremarkable coronary arteries.