Outcome-linked Left Internal Mammary Artery to Left Anterior Descending Artery Graft Flow Threshold and Quantitative Flow Ratio-based Low-flow Prediction in Off-pump Coronary Artery Bypass Grafting.

Transit-time flow measurement (TTFM) is used during coronary artery bypass grafting (CABG), but outcome-linked thresholds for low left internal mammary artery-left anterior descending artery (LIMA-LAD) mean graft flow (MGF) and preoperative low-flow predictors remain limited. This single-center retrospective study included 282 patients undergoing elective off-pump CABG with LIMA-LAD grafting. Restricted cubic spline and segmented regression examined the association between MGF and peak high-sensitivity cardiac troponin I (hs-cTnI) within 48 hours, and logistic regression evaluated associations with in-hospital major adverse cardiac and cerebrovascular events (MACCE) and developed a preoperative low-flow prediction model. LIMA-LAD MGF showed a nonlinear association with peak hs-cTnI, with an inflection point at 31 ml/min. Flow <31 ml/min was associated with higher hs-cTnI levels and higher adjusted in-hospital MACCE risk in the main model (34 events; adjusted odds ratio [OR] 2.53, 95% confidence interval [CI] 1.21 to 5.44; p = 0.014). In a sensitivity model additionally adjusted for obtuse marginal/left circumflex-territory grafting, the association was attenuated but remained directionally consistent (OR 2.10, 95% CI 0.99 to 4.46; p = 0.053). Higher LAD quantitative flow ratio (QFR) and smaller distal vessel diameter independently predicted low flow. In conclusion, a LIMA-LAD MGF threshold of 31 ml/min was associated with greater perioperative myocardial injury and higher in-hospital event risk, and a QFR-based model may support perioperative risk stratification pending external validation with standardized 30-day outcomes.