Adaptive changes in autogenous vein grafts for arterial reconstruction: clinical implications

Abstract

For patients with the most severe manifestations of lower extremity arterial occlusive disease, bypass surgery using autogenous vein has been the most durable reconstruction. However, the incidence of bypass graft stenosis and graft failure remains substantial and wholesale improvements in patency are lacking. One potential explanation is that stenosis arises not only from over exuberant intimal hyperplasia, but also due to insufficient adaptation or remodeling of the vein to the arterial environment. Although in vivo human studies are difficult to conduct, recent advances in imaging technology have made possible a more comprehensive structural examination of vein bypass maturation. This review summarizes recent translational efforts to understand the structural and functional properties of human vein grafts and places it within the context of the rich existing literature of vein graft failure.

Figure 1

While the mean bypass graft lumen increases about 22% over the first 6 months following implantation, A, considerable variability exists between individual grafts, B. Early luminal remodeling is correlated with initial shear stress at the time of implantation, C. Temporally distinct from luminal remodeling, the vein graft significantly stiffens between 1 and 3 months following implantation, D. Adapted from reference .

Figure 2

Vein graft lumen change (percent) from implantation to 1 month in a population undergoing lower extremity bypass grafting for arterial occlusive disease. Luminal measurements were made with high resolution M-mode ultrasound at the same location of the vein graft for the operative and the 1 month assessment. By dichotomizing the population by baseline plasma CRP levels above and below 5 mg/L, disparate early luminal remodeling patterns of the vein graft become apparent, 37% vs 10 %, P=.0072. Thus, patients with high levels of systemic inflammation have impaired ability to positively remodel vein grafts, adapted from reference .

Figure 3

Modes of vein graft failure. While the majority of intimal hyperplasia in vein grafts is focal, a substantial minority (12%) is diffuse. Panel A represents a 6 month old vein graft in a 67 year old white man that developed a mid graft stenosis (arrow) that was successfully treated with a vein patch angioplasty. Panel B represents a 4 month old vein graft in a 77 year Black women undergoing angiography for contralateral limb ischemia. Three months later, she developed diffuse intimal hyperplasia which progressed to vein graft occlusion.

Figure 4

Histologic sections (10X) of an 8 month old vein graft which developed a focal mid-graft stenosis and underwent open revision with a short interposition graft. The vein was of uniform size and caliber at the time of implantation. The sections were taken approximately 2 cm from one another. The area of stenosis has developed marked intimal hyperplasia and has a smaller area circumscribed by the internal elastic laminae as well as decreased total vessel diameter indicative of negative remodeling of the entire vein graft, A. Theoretical normal and abnormal adaptation patterns of a human lower extremity vein grafts, B. Normally the lumen and wall area increase in the early post-implantation period to produce a lumen diameter to wall thickness ratio of about 7.

Figure 5

Flow mediated vasodilation in mature human saphenous vein grafts demonstrates a functional endothelium. Application of an occlusive blood pressure cuff (220 mmHg) to the proximal calf of a cohort of patients undergoing femoro-popliteal bypass grafts for 5 minutes produces an increase in blood flow and shear stress within the graft, A. In this cohort, flow mediated, endothelium dependent vasodilation was 5.3% and nitroglycerin mediated, endothelium independent (0.4 mg sublingual nitroglycerin) dilation was 3.7%.