Rhee, Robert Y.

Experiments were designed to compare perioperative blood loss, early thrombogenicity and morphologic and functional characteristics of the neointima of three types of prosthetic materials used for carotid artery patch angioplasty. Bilateral carotid patch angioplasties were performed in 20 dogs, using 20 gelatin-impregnated fluoropassivated Dacron (GIF), 10 untreated knitted Dacron and 10 expanded polytetrafluoroethylene (PTFE) patches (5 cm2). Intraoperative blood loss, platelet deposition at 24 h and neointimal morphology at 6 weeks after the operation were assessed. Bioassay of the neointima was performed at 6 weeks in 16 patches. Mean (s.e.m.) blood loss was significantly less in GIF patches (14.7 (2.7) ml) compared with either PTFE (75.6 (24) ml) or untreated Dacron (64. 3 (9.5)) ( P < 0.005). Mean (s.e.m.) platelet deposition in GIF patches (1380 (328) platelets/cm2) was approximately 50% less at 24 h than in untreated Dacron (2562 (1035) platelets/cm2) or PTFE (2140 (998) platelets/cm2) patches ( P < 0.05). Neointimal coverage was greater in PTFE (94 (1.3%)) compared with GIF (79 (2.7%)) or untreated Dacron (86(2.4%)) patches ( P < 0.05). The thickness of the neointimal layer of PTFE (0.5 (0.01) mm) patches was greater than other patch types; GIF (0.2 (0.01) mm) or untreated Dacron (0.3 (0.01) mm) ( P < 0.05). Under bioassay conditions, acetylcholine caused release of vasoactive relaxing factor(s) from all patches. However, relaxations from baseline were less with GIF patches (−37.9 (11.7)% versus −54.5 (9.6) for untreated Dacron; −50.2 (15.2)% for PTFE) ( P = n.s.). Endothelin-1 release occurred from all patches and was increased with the extent of neointimal coverage. These data demonstrate that GIF patches caused the least perioperative bleeding, were the least thrombogenic at 24 h and developed the thinnest neointima at 6 weeks. All patch materials developed a functioning neointima.

Increased shear, pressure, and oxygen tension in vein grafts may alter production of endothelium-derived vasoactive and anti-mitogenic factors such as nitric oxide which subsequently affect development of neointimal hyperplasia. This study was designed to determine whether or not nitric oxide mediates endothelium-dependent responses in femoral in situ vein grafts. Non-reversed, canine femoral vein grafts were placed bilaterally to bypass a ligated segment of the femoral artery in dogs. After 6 weeks, the grafts were removed, cut into rings, and suspended in organ chambers for measurement of isometric force. In some rings the endothelium was removed deliberately. In the presence of indomethacin, the synthetic analog of L-arginine, L-NG-monomethyl-arginine (10−4 M: L-NMMA) did not cause a significant change in baseline tension of rings with endothelium. L-NMMA reduced only contractions of rings with endothelium to the alpha-adrenergic agonist UK 14,304. The analog also reduced maximal relaxations to the calcium-ionophore, A23187 in rings with endothelium. In addition, L-NMMA reduced relaxations of rings without endothelium to adenosine diphosphate by 35%. Positive immunostaining for nitric oxide synthase was present in both the myointima and media of histological sections of grafts. In conclusion, these results suggest that in situ vein grafts exhibit two unique properties which are unlike unoperated arteries or veins: (i) alpha2-adrenergic receptors may be coupled to the release of contractile endothelium-derived factors associated with production of nitric oxide; and (ii) nitric oxide may be released by the smooth muscle in response to purinergic stimulation. The presence of nitric oxide synthase throughout the wall of the graft may result in production of nitric oxide in response to adenosine diphosphate released by platelets and to circulating catecholamines.

Successful replacements of the superior vena cava (SVC) using autogenous saphenous or superficial femoral vein or prosthetic grafts have been previously performed, but the use of allograft for treatment of SVC syndrome has not been reported. The patient treated by the authors was a forty-one-year-old woman who presented with severe venous congestion of the head and neck caused by fibrosing mediastinitis. In addition, she had sclerosing cholangitis and chronic liver failure. To treat her SVC syndrome and provide access for fluid and blood transfusion and for possible venovenous bypass, SVC reconstruction was performed concomitant to orthotopic liver transplantation. A left innominate vein-right atrial bypass was inserted using an iliocaval allograft. The patient had an uncomplicated recovery, and at six months after surgery her SVC allograft is widely patent and her transplanted liver is functioning well. The venous allograft is an excellent conduit for those patients who are receiving immunosuppression therapy to avoid rejection of a transplanted organ.