Internal mammary arteries (IMA) are routinely used as conduits in CABG surgery given their superior long-term patency rates and high resistance to atherosclerosis. These conduits can be harvested pedicled, whereby the IMA is dissected along with its surrounding fascia including blood and nerve supplies (i.e. preserving the milieu of the conduit) or skeletonized, whereby the IMA is dissected from its surrounding blood supply, innervation, lymphatics, muscle and fascia (i.e. preserving the milieu of the sternum). Despite the positive effects of skeletonization on graft length and sternal wound infections, few prospective studies have examined the effect of that harvesting technique on angiographic endpoints and therefore it remains unclear whether skeletonization adversely affects the risk of graft failure. We conducted a substudy of 1,448 COMPASS trail patients randomized 4 to 14 days after CABG surgery to receive rivaroxaban, aspirin, or both and underwent a follow-up CT angiogram after 1 year. Graft failure was diagnosed by CT angiogram and included grafts with string signs in addition to complete occlusion. We present an analysis of 1,066 IMA grafts grafts examining the impact of graft harvesting technique (pedicled vs. skeletonized) on graft failure 1 year after CABG surgery. Baseline characteristics of the 3 treatment groups were similar and no differences in graft failure rates were observed between drug treatments. The rate of graft failure was 6.1% (46/752) in the pedicled IMA group versus 12.4% (39/314) in the skeletonized IMA group (odds ratio 2.18; 95% CI 1.39 to 3.41; P < 0.001). Similarly, in pedicled left-IMA (LIMA) the rate of graft failure was 5.4% compared to 9.6% in skeletonized LIMA grafts (odds ratio 1.87; 95% CI 1.11 to 3.13; P=0.02). A trend of graft failure was observed as well between pedicled (23.3%; 7/30) and skeletonized (29.5%; 13/44) in right-IMA (RIMA) grafts (odds ratio 1.38; 95% CI 0.48 to 4.00; P=0.55). The skeletonized harvesting technique is associated with a significant increase in IMA graft failure 1 year after CABG surgery compared to the pedicled technique. Further investigation of the impact of the skeletonized technique on the risk of graft failure is warranted before advocating for its widespread use.