The geometry and mechanics of saphenous vein patch angioplasty after carotid endarterectomy

Abstract

To elucidate some of the mechanisms that may account for the potential advantages and disadvantages of saphenous vein patch angioplasty (VPA) after endarterectomy of the carotid artery, the author evaluated 50 VPAs with respect to geometry, blood-flow velocities, and wall mechanics. The mean internal carotid artery (ICA) diameter cephalad to the vein patch was 4.5 mm, whereas the mean diameter of the patched segment was 7.4 mm. The mean ratio between the cross-sectional area of the patched ICA and the cross-sectional area calculated as if the artery were nonpatched was 2.9. In the presence of restenosis sufficient to occlude the nonpatched artery, this ratio was decreased to 1.9 when the artery alone was stenosed and to 0.49 when both the artery and the vein patch were stenosed. The mean ratio between the peak blood-flow velocity distal to the patch and the blood-flow velocity in the patched segment was 3.4. These area and velocity ratios indicate that the wall shear stress in the patched segment was three to five times lower than that in the distal ICA. The normal stress in the circumferential vein patch wall was two to three times greater than that in veins used as bypass grafts at the same intraluminal pressure. In comparison to primary arteriotomy closure after carotid endarterectomy, VPA provides a partially endothelialized flow surface, a significantly greater cross-sectional area, and a relatively mild wall shear stress; all three of these factors may protect the artery against both hemodynamically significant restenosis and early post-operative thrombosis.