Coronary artery bypass grafting(CABG) is the golden standard for severe coronary artery disease(CAD), the current surgery strategy is mainly based on coronary angiography(CAG), but many trials of PCI have shown that visually stenosis in CAG may not have functional significance. The aim of this study is to investigate if the Quantitative Flow Ratio (QFR) can be adopted in CABG and achieve a better graft patency.

CABG is the major treatment of three vessels or left main disease. CAG is the main basis on choosing the vessels to graft, however, some of the grafts occluded shortly after surgery due to competitive flow, these vessels may not be significantly stenosis in functional assessment such as Fractional Flow Reserve (FFR). Quantitative Flow Ratio (QFR) is a novel method for evaluating the functional significance of coronary stenosis. Comparing to FFR, there is no need for pressure wire or ATP when performing QFR. This study plan to investigate the clinical effect of QFR in CABG, all patients included will be allocated 1:1 into two groups: QFR-guided and Angio-guided, QFR-guided group will be performed a CABG based on the result of QFR, the other group will be based on heart team discussion of CAG, CTA will be adopted to evaluate the 1 year graft patency.

Inclusion Criteria:

• patients with evidence of angina pectoris
• left main or three vessels disease, have the indication for CABG after discussion of the heart team
• at least one main vessels stenosis on 40%-70%

Exclusion Criteria:

• former cardiac surgery patients
• need to perform other cardiac or major surgery( i.e. valve surgery, carotid endarterectomy
• emergent CABG
• acute myocardial infarction time less than 7 days
• life expectancy less than 3 years

QFR will be masked to care providers and participants, and open to investigators, the allocation will be based on QFR.