Association of preoperative quantitative flow ratio with 1-year graft patency after coronary artery bypass grafting: A two-center retrospective cohort study

BACKGROUND: Coronary artery bypass grafting (CABG) targets are selected by angiographic stenosis, whereas percutaneous coronary intervention increasingly relies on functional assessment. Whether quantitative flow ratio (QFR), a wire-free angiography-derived index, relates to graft outcomes is unclear. We examined preoperative QFR and 1-year graft patency. METHODS: We retrospectively studied 491 patients undergoing isolated CABG at two heart centers, 2006-2019. Investigators blinded to bypass design and outcome measured preoperative QFR in all analyzable major vessels. Protocol angiography assessed 1-year graft status. Generalized estimating equations accounting for within-patient clustering related QFR (per 0.1-unit increment) to graft occlusion, unadjusted and adjusted for target vessel, graft type, age, sex, diabetes, and ejection fraction. Linearity and effect modification by graft type and target territory were assessed. RESULTS: Median QFR among 1161 analyzable vessels was 0.66 (interquartile range, 0.48-0.80); among 1036 bypassed vessels, higher QFR was associated with greater 1-year graft occlusion risk (unadjusted odds ratio [OR], 1.27; 95% confidence interval [CI], 1.15-1.42; adjusted OR, 1.15; 95% CI, 1.04-1.27; p = 0.008). The association was linear (standardized occlusion probability, 8.2% at QFR 0.50; 13.1% at 0.90). Effect modification by target territory was borderline (joint interaction p = 0.025; Holm-adjusted p = 0.050); this exploratory finding requires confirmation. Graft type did not modify the association (p = 0.28). CONCLUSIONS: Higher preoperative QFR, indicating functionally less significant stenosis, was associated with greater 1-year graft occlusion risk. This hypothesis-generating, group-level association establishes neither causation nor predictive utility for individual grafts. Prospective validation is needed.