| Summary: | Background In coronary artery bypass grafting, grafting a target vessel with nonsignificant stenosis increases the risk of graft failure. The present study aims to investigate the impact of preoperative quantitative flow ratio (QFR), a novel functional assessment of the coronary artery, on internal mammary artery graft failure rate and midterm patient outcomes. Methods and Results Between January 2016 and January 2020, we retrospectively included 419 patients who underwent coronary artery bypass grafting who had received preoperative angiography and postoperative coronary computed tomographic angiography in our center. QFR of the left anterior descending (LAD) artery was computed based on preoperative angiograms. The primary end point was the failure of the graft on the LAD artery assessed by coronary computed tomographic angiography at 1 year, and the secondary end point was major adverse cardiac and cerebrovascular events including death from any cause, myocardial infarction, stroke, or repeat revascularization. Grafts on functionally nonsignificant LAD arteries (QFR >0.80) had a significantly higher failure rate than those on functionally significant LAD arteries (31.4% versus 7.2%, P<0.001). QFR outperforms degree of stenosis in discriminating graft failure (C statistic, 0.76 versus 0.58). Clinical follow‐up (3.6 years, interquartile range [3.3–4.1]) was accomplished in 405 patients, and the rate of major adverse cardiac and cerebrovascular events was significantly higher among patients with functionally nonsignificant LAD arteries (10.1% versus 4.2%; adjusted hazard ratio, 3.08 [95% CI, 1.18–8.06]; P=0.022). Conclusions In patients receiving internal mammary artery to LAD artery coronary artery bypass grafting, preoperative QFR of the LAD artery of >0.80 was associated with a higher graft failure rate at 1 year and worse patient outcomes at the 3.6‐year follow‐up.
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