THE PROTECTIVE EFFECT OF VEIN CUFFED ANASTOMOSES IS NOT MECHANICAL INORIGIN

Purpose: Intimal hyperplasia (IH) is a proliferative process of vascul ar smooth muscle cells that occurs after an arterial injury, particula rly at outflow anastomoses of prosthetic bypass grafts. IH causes sten osis that leads ultimately to graft flow reduction and thrombosis. We have demonstrated previously that vein cuff interposition between an e xpanded polytetrafluoroethylene (e-PTFE) graft and artery at distal an astomoses diminished IH formation in the arterial outflow as compared with noncuffed anastomoses. Improved long-term patency rates associate d with the placement of an interposition vein cuff at the distal anast omosis of e-PTFE grafts to infrageniculate arteries have also been dem onstrated clinically. This study examined the mechanical factors that may contribute to the protective effect of cuffed anastomoses. These f actors include the expansibility of the vein cuff as compared with e-P TFE, as well as the angle of the cuffed anastomosis. Methods: Compatib le animals were selected by use of platelet aggregation studies. Nine dogs, group A, received a 4 mm e-PTFE graft plus a 1 cm long interposi tion vein cuff at the distal anastomosis in the left carotid artery. T he same procedure was done on the right side, and in addition the vein cuff was encircled by an e-PTFE jacket incorporated into the anastomo sis to prevent the expansion of the vein cuff with arterial pulsation. To study the effect of distal anastomotic angle and geometry on the f ormation of IH, five dogs, group B, received a 4 mm e-PTFE graft in bo th sides. On the left, the distal anastomosis was performed between th e graft and the artery at an acute angle as it is commonly done when a bypass graft is placed. On the right side a 1 cm long, 6 mm diameter e-PTFE segment was interposed between the artery and the graft at a pe rpendicular angle. This geometry mimicked the right angle of a vein cu ff-to-artery anastomosis. After 10 weeks the grafts were harvested, an d the thickness of IH was measured with an ocular micrometer under lig ht microscopy. Results: In group A, one dog had bilateral graft thromb osis (12%), and these grafts were discarded. In the remaining eight do gs there was no statistically significant difference in the thickness of IH between the right (jacketed group) and the left side (nonjackete d/control group), showing that vein cuff expansibility did not play a role in protecting against the formation of IH. In group B, bilateral graft thrombosis occurred in four of five dogs (80%), suggesting that the perpendicular anastomotic angle was not protective. Conclusion: Th ese results suggested that the protective effect of the vein cuff is n ot mechanical in origin.