Vasa vasorum inside out/outside in communication: a potential role in the patency of saphenous vein coronary artery bypass grafts

Abstract

The saphenous vein (SV) is the most commonly used conduit for revascularization in patients undergoing coronary artery bypass surgery (CABG). The patency rate of this vessel is inferior to the internal thoracic artery (ITA). In the majority of CABG procedures the ITA is removed with its outer pedicle intact whereas the (human) SV (hSV) is harvested with pedicle removed. The vasa vasorum, a microvessel network providing the adventitia and media with oxygen and nutrients, is more pronounced and penetrates deeper towards the lumen in veins than in arteries. When prepared in conventional CABG the vascular trauma caused when removing the hSV pedicle damages the vasa vasorum, a situation affecting transmural flow potentially impacting on graft performance. In patients, where the hSV is harvested with pedicle intact, the vasa vasorum is preserved and transmural blood flow restored at graft insertion and completion of CABG. By maintaining blood supply to the hSV wall, apart from oxygen and nutrients, the vasa vasorum may also transport factors potentially beneficial to graft performance. Studies, using either corrosion casts or India ink, have shown the course of vasa vasorum in animal SV as well as in hSV. In addition, there is some evidence that vasa vasorum of hSV terminate in the vessel lumen based on ex vivo perfusion, histological and ultrastructural studies. This review describes the preparation of the hSV as a bypass conduit in CABG and its performance compared with the ITA as well as how and why its patency might be improved by harvesting with minimal trauma in a way that preserves an intact vasa vasorum.

Recent Developments in Vascular Adventitial Pathobiology

“…The VV plays a crucial role in veins given that luminal oxygen and nutrient levels are low in these blood vessels in comparison to arteries. 22 Therefore, the VV of veins penetrate closer to the intima than those of arteries, and the role of the VV of veins in venous disease remains unclear. 22 Little is known about adventitial lymphatic VV, especially in disease.…”

“…22 Therefore, the VV of veins penetrate closer to the intima than those of arteries, and the role of the VV of veins in venous disease remains unclear. 22 Little is known about adventitial lymphatic VV, especially in disease. They are in close proximity to the arterial VV and appear to be, in contrast to the arterial VV, more dense in the infrarenal abdominal aorta.…”

A Brief Comment on Vasa Vasorum of Human Saphenous Vein: relevance for Coronary Artery Bypass Surgery

“…The importance of the vasa vasorum in the performance (patency) of human saphenous vein (hSV) used for coronary artery bypass grafting (CABG) has been highlighted in various publications over the last 15 years [ 1 - 9 ] . It has been pointed out that the vasa system not only plays a role in delivering oxygen and nutrients to the vein wall - as it is generally accepted - but it also may act as a novel 'transport system' [ 10 ] . Principally the vasa vessels, including those located in the adventitia and those associated with the vein's surrounding pedicle of fat [ 11 ] , protect the hSV once implanted as grafts during CABG.…”

“…Also note that the arrows indicate a possible direction of blood flow - from the vein lumen into the openings of vasa to be then delivered to the vein wall following vein implantation as coronary graft. For more details on the aspects of blood flow in hSV as coronary graft, see Loesch and Dashwood [ 10 ] , 2018. SV=saphenous vein …”

“…Lower panel: Conventionally harvested hSV where the adventitia has been stripped off or damaged; the vasa vasorum is constricted or occluded, blood flow to the vein wall is reduced releasing hypoxic factors, which are associated with many aspects of graft failure. For more details, see Samano et al [ 22 ] , 2015, and Loesch and Dashwood [ 10 ] , 2018. From an Open Access article: Loesch and Dashwood [ 10 ] , 2018, which is acknowledged.…”