Comparison of Fractional Flow Reserve and Resting Full-Cycle Ratio in the Functional Assessment of Coronary Artery Stenosis in Patients with Non-ST-Segment Elevation Acute Coronary Syndrome

Background : This study investigated factors influencing discrepancies between fractional flow reserve (FFR) and resting full-cycle ratio (RFR) in the functional assessment of coronary artery stenosis in patients with non-ST-segment elevation acute coronary syndrome (NSTE-ACS). Methods : We included 320 diseased vessels from 253 consecutive patients with NSTE-ACS. Vessels were categorized into four groups based on FFR ≤ 0.80 and RFR ≤ 0.89 thresholds: group 1 concordant negative (RFR–/FFR–), group 2 positive RFR and negative FFR (RFR+/FFR–), group 3 negative RFR and positive FFR (RFR–/FFR+), and group 4 concordant positive (RFR+/FFR+). Univariate and multivariate logistic regression analyses were conducted to identify predictors of diagnostic discrepancy between FFR and RFR. Results : Of the 320 diseased vessels, 182 (56.9%) were in group 1 (RFR–/FFR–), 33 (10.3%) in group 2 (RFR+/FFR–), 31 (9.7%) in group 3 (RFR–/FFR+), and 74 (23.1%) in group 4 (RFR+/FFR+). The concordance between FFR and RFR was 80.0%. No-tably, left anterior descending artery (LAD) lesions exhibited significantly lower consistency compared to non-LAD lesions ( p = 0.001), with distinct differences in FFR and RFR values between these groups ( p < 0.001). The presence of a LAD lesion emerged as an independent predictor of diagnostic inconsistency between positive RFR and negative FFR measurements ( p = 0.001). Conclusions : LAD involvement independently predicts diagnostic discrepancies between FFR and RFR in evaluating functional coronary artery stenosis in NSTE-ACS patients.