Objective To compare the surgical outcomes between conventional coronary artery bypass grafting (CABG) and minimally invasive direct coronary artery bypass grafting via left small thoracotomy stratified by different levels of non-invasive fractional flow reserve computed tomography (FFR-CT), and to explore the recommended FFR-CT cut-off values for selecting appropriate coronary vessels for grafting in the two surgical procedures. MethodsA retrospective enrollment was conducted on patients who underwent isolated CABG at the Minimally Invasive Cardiac Surgery Center of Beijing Anzhen Hospital from 2022 to 2025, including conventional median sternotomy CABG and minimally invasive CABG. Clinical data comprising preoperative FFR-CT of target vessels, preoperative coronary angiography, intraoperative instantaneous flow of corresponding bypass grafts, peak postoperative troponin level, postoperative graft patency after discharge, and the incidence of major adverse cardiovascular and cerebrovascular event (MACCE) were collected. Patients were divided into two groups according to FFR-CT value: FFR-CT＞0.80 and FFR-CT≤0.80. Intraoperative graft flow was classified into three grades: Grade 1 (flow≤30 mL/min), Grade 2 (30 mL/min＜flow≤60 mL/min), and Grade 3 (flow＞60 mL/min). The differences in intraoperative flow corresponding to different FFR-CT levels were compared between patients undergoing conventional CABG and minimally invasive CABG respectively, and regression analyses were performed separately. Postoperative troponin was also graded into three levels: Grade 1 (troponin I＜2 000 ng/L), Grade 2 (2 000 ng/L≤troponin I＜5 000 ng/L), and Grade 3 (troponin I≥5 000 ng/L). Troponin I levels were compared between the two groups. ResultsA total of 390 patients with 928 target vessels were enrolled, including 207 patients undergoing conventional CABG (542 target vessels; 153 males and 54 females, aged 43-81 years) and 183 patients undergoing minimally invasive CABG (386 target vessels; 144 males and 39 females, aged 46-84 years). For conventional CABG, target vessels with FFR-CT≤0.80 presented better intraoperative graft flow. The regression equation was Q (flow grade)=–3.077FFR3+3.455. FFR-CT＜0.78 was recommended to achieve optimal intraoperative graft flow. For minimally invasive CABG, superior intraoperative graft flow was also observed in target vessels with FFR-CT≤0.80, with the regression equation Q (flow grade)=–24.560FFR2+30.207FFR–6.492, and the recommended cut-off value was FFR-CT＜0.80. For coronary arteries with angiographically moderate stenosis, intraoperative graft flow differed significantly among different FFR-CT subgroups (P＜0.001), with higher flow in the FFR-CT≤0.80 group. Moreover, lower FFR-CT value of target vessels was associated with lower peak postoperative troponin I level. ConclusionFFR-CT serves as a reliable reference indicator for target vessel selection in conventional CABG and left small thoracotomy minimally invasive CABG, especially for coronary lesions with angiographically moderate stenosis. In addition, FFR-CT has certain predictive value for postoperative surgical efficacy.