Norberto J J, Sidawy A N, Trad K S, Jones B A, Neville R F, Najjar S F, Sidawy M K, DePalma R G
Department of Surgery, George Washington University, Washington, DC, USA.
J Vasc Surg. 1995 Apr;21(4):558-64; discussion 564-6. doi: 10.1016/s0741-5214(95)70187-7.
Intimal hyperplasia (IH) is a proliferative process of vascular smooth muscle cells that occurs after an arterial injury, particularly at outflow anastomoses of prosthetic bypass grafts. IH causes stenosis that leads ultimately to graft flow reduction and thrombosis. We have demonstrated previously that vein cuff interposition between an expanded polytetrafluoroethylene (e-PTFE) graft and artery at distal anastomoses diminished IH formation in the arterial outflow as compared with noncuffed anastomoses. Improved long-term patency rates associated with the placement of an interposition vein cuff at the distal anastomosis of e-PTFE grafts to infrageniculate arteries have also been demonstrated clinically. This study examined the mechanical factors that may contribute to the protective effect of cuffed anastomoses. These factors include the expansibility of the vein cuff as compared with e-PTFE, as well as the angle of the cuffed anastomosis.
Compatible 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 interposition vein cuff at the distal anastomosis in the left carotid artery. The same procedure was done on the right side, and in addition the vein cuff was encircled by an e-PTFE jacket incorporated into the anastomosis to prevent the expansion of the vein cuff with arterial pulsation. To study the effect of distal anastomotic angle and geometry on the formation of IH, five dogs, group B, received a 4 mm e-PTFE graft in both sides. On the left, the distal anastomosis was performed between the 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 perpendicular angle. This geometry mimicked the right angle of a vein cuff-to-artery anastomosis. After 10 weeks the grafts were harvested, and the thickness of IH was measured with an ocular micrometer under light microscopy.
In group A, one dog had bilateral graft thrombosis (12%), and these grafts were discarded. In the remaining eight dogs there was no statistically significant difference in the thickness of IH between the right (jacketed group) and the left side (nonjacketed/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.
These results suggested that the protective effect of the vein cuff is not mechanical in origin.
内膜增生（IH）是动脉损伤后血管平滑肌细胞的增殖过程，尤其发生在人工血管旁路移植的流出道吻合口处。内膜增生导致管腔狭窄，最终致使移植血管血流减少并形成血栓。我们之前已经证明，与无袖套吻合相比，在远心端吻合口处的膨体聚四氟乙烯（e-PTFE）移植血管与动脉之间插入静脉袖套可减少动脉流出道内膜增生的形成。临床研究也证实，在e-PTFE移植血管与膝下动脉的远心端吻合口处放置静脉袖套可提高长期通畅率。本研究探讨了可能有助于带袖套吻合口起到保护作用的力学因素。这些因素包括与e-PTFE相比静脉袖套的可扩张性，以及带袖套吻合口的角度。
通过血小板聚集研究选择合适的动物。9只犬（A组）在左颈动脉远心端吻合口处接受4mm的e-PTFE移植血管加1cm长的静脉袖套。右侧进行相同操作，此外，静脉袖套被并入吻合口的e-PTFE外套环绕，以防止静脉袖套随动脉搏动扩张。为了研究远心端吻合口角度和几何形状对内膜增生形成的影响，5只犬（B组）双侧均接受4mm的e-PTFE移植血管。左侧，移植血管与动脉之间以锐角进行远心端吻合，这是放置旁路移植血管时常用的方式。右侧，在动脉与移植血管之间以直角插入一段1cm长、直径6mm的e-PTFE节段。这种几何形状模拟了静脉袖套与动脉吻合的直角。10周后取出移植血管，在光学显微镜下用目镜测微计测量内膜增生的厚度。
A组中，1只犬双侧移植血管发生血栓形成（12%），这些移植血管被丢弃。在其余8只犬中，右侧（带外套组）和左侧（无外套/对照组）内膜增生厚度无统计学显著差异，表明静脉袖套的可扩张性在预防内膜增生形成方面不起作用。B组中，5只犬中有4只（80%）双侧移植血管发生血栓形成，提示直角吻合角度并无保护作用。
这些结果表明，静脉袖套的保护作用并非源于力学因素。
