Perioperative suppression of platelet adherence to small-diameter polytetrafluoroethylene (PTFE) grafts

The perioperative effect of platelet antagonists on small-diameter polytetrafluoroethylene (PTFE) grafts was evaluated in forty-six New Zealand white male rabbits receiving either dipyridamole (DPM) 100 mg/kg/day (n = 10; group 1), aspirin (ASA) 10 mg/kg/day (n = 10; group 2), a combination of ASA 10 mg/kg/day and DPM 10 mg/kg/day (n = 9; group 3) or 100 mg/kg/day (n = 10; group 4), or placebo (n = 7) as single daily doses. All regimens began 72 hr prior to insertion of a 20 x 3-mm internal diameter PTFE interposition aortic graft. Autologous indium-111 labeled platelets were injected immediately after implantation. Graft and an equivalent segment of aorta were harvested after 48 hr. Graft platelet adherence index (GPAI) was calculated as the graft:reference aorta ratio of emissions. The GPAI in the control group was 238 +/- 46 (mean +/- SD). Single regimen antiplatelet agents in groups 1 and 2 reduced mean GPAI to 47 +/- 38 and 40 +/- 12, respectively. The combination regimen in group 3 lowered mean GPAI to 43 +/- 8 and in group 4 to 21 +/- 7. Platelet uptake in PTFE grafts at 48 hr is significantly lowered to 8.8 to 19.7% of control by perioperative antiplatelet agents given as a single daily oral dose (P less than 0.001). ASA alone and DPM alone provided similar suppression of platelet uptake, but combination ASA + low dose or high dose DPM gave significantly greater (P less than 0.001) suppression of early platelet deposition than the single agent regimens. These results support perioperative administration of combination oral antiplatelet agents as adjunctive therapy in small diameter prosthetic graft implantation.     

Penile corporoplasty with polytetrafluoroethylene (PTFE) grafts

Ten male dogs underwent segmental excision of tunica albuginea of corpus cavernosum penis and replacement with polytetrafluoroethylene grafts. None of the dogs exhibited acute or chronic adverse reaction to the graft. These findings suggest that PTFE may have a role in human reconstructive phalloplasty.     

A prospective randomized study of three expanded polytetrafluoroethylene (PTFE) grafts as small arterial substitutes.

A prospective, double-blind, randomized study was performed to determine the relative patency rate of polytetrafluoroethylene (PTFE) grafts, Gore-Tex, Impra, and a Surgikos prototype PTFE graft. The 48 grafts (40 x 4 mm) replaced excised segments of femoral arteries in adult mongrel dogs, whose mean weight was 20.6 +/- 0.9 kg; the grafts were removed after 12 weeks. Sterile technique and antibiotic therapy were included in the study. Anticoagulation was not employed. Anastomoses were performed with 6 = 0 polypropylene. Angiographic assessment of each anastomosis was made at surgery and prior to sacrifice. Patency was assessed daily by palpation and Doppler flow signals, as well as angiographically, prior to sacrifice. The overall patency rate was 62.5%. There were no statistically significant differences in patency rates among the three groups (Gore-Tex, 56%; Impra, 75%, Surgikos, 56%). Histologic evaluation revealed incomplete neointima formation and significant pannus formation in all three types of grafts without any significant discernible difference among them. The results suggest that further experimental evaluation of PTFE, as a small vessel substitute, is indicated prior to its use clinically in preference to autogenous vein.     

Spontaneous re-canalization of thrombosed polytetrafluoroethylene (PTFE) grafts

Fibrinolysis is an important hemostatic process initiated either by tissue plasminogen activator (tPA) or pro-urokinase (pro-UK) released from endothelial cells. These agents act preferentially on plasminogen by converting it to the active molecule plasmin. This initiates the clot lysis process, which may take several days for completion. Most patients with end-stage renal disease (ESRD) have PTFE grafts for chronic hemodialysis. When these grafts are thrombosed, they are either surgically revised or percutaneously thrombolysed. When these measures fail another access is created without removing the clotted graft. However, it is possible that de-clotting of these thrombosed PTFE grafts can occur spontaneously. Once the graft develops an endothelial lining, these cells can contribute to the fibrinolytic process by secreting tPA or pro-UK. Because this endothelial lining may be less developed than that of a normal vessel, the fibrinolytic process may occur at a slower rate or not at all. Frequent cannulation during hemodialysis can denude existing endothelium, further contributing to the inadequacy of the graft to initiate thrombolysis. In practice, once the PTFE is clotted, the graft is ignored if it is not considered for declotting. In such circumstances the re-canalization process could be overlooked, re-sulting in the unnecessary placement of additional accesses. Presented here are three patients with clotted grafts in which re-canalization occurred without intervention.     

Light and electron microscopy of polytetrafluoroethylene arterial grafts in dogs

Reinforced expanded polytetrafluoroethylene grafts with fibril lengths of approximately 17 to 25 micrometers were inserted into the infrarenal aorta of dogs for periods ranging from 24 hours to eight months. The grafts were studied by light and electron microscopy, which showed that polytetrafluoroethylene consists of ridges or nodes connected by fibrils. Initially red blood cells passed down in the pores of the polytetrafluoroethylene, and then the surface was covered with fibrin. A new endothelium developed by the twelfth day. The new intimal lining became thicker owing to the appearance of smooth muscle cells deep to the endothelial cells, forming a neointima 120 micrometers thick by eight months. Fibroblasts and collagen penetrated the graft, but vasa vasorum did not, although they were present in the external connective tissue.     

Neoendothelialization of small-diameter polytetrafluoroethylene arterial grafts is not delayed by aspirin and dipyridamole

The effect of aspirin and dipyridamole on neoendothelialization of polytetrafluoroethylene (PTFE) was studied in the rabbit aortic graft model. Forty-three New Zealand white rabbits were allocated to receive a combination of aspirin 10 mg/kg/day and dipyridamole 10 mg/kg/day (n = 23) or placebo (n = 20). Both regimens began 3 days before insertion of PTFE aortic grafts (10 mm long and 3 mm internal diameter). Serum thromboxane B2 concentration in the control group averaged 254 +/- 22 ng/ml (+/- standard error of the mean) and 40 +/- 23 ng/ml in the treatment group (p less than 0.001). Grafts and adjacent aorta were harvested at 2 weeks (n = 4), 4 weeks (n = 9), 8 weeks (n = 13), and 12 weeks (n = 17) after implantation. Morphologic techniques, including conventional light microscopy, immunoperoxidase staining for endothelial factor VIII-related antigen, and scanning electron microscopy (SEM) demonstrated that neointima was composed of endothelial cells arising by ingrowth at anastomotic site and as islands in the center of the graft. The percentage of graft neoendothelialization was measured by SEM. At 2 weeks 18% +/- 2% of the PTFE surface was covered with endothelium in the aspirin/dipyridamole group. The percentages of graft neoendothelialization for the treatment and control groups at 4 weeks were 44% +/- 13% (n = 5) and 46% +/- 10% (n = 4) (p = NS), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Below-knee femoropopliteal bypass using externally supported polytetrafluoroethylene (PTFE) grafts

Twenty-seven externally supported polytetrafluoroethylene (PTFE) grafts were implanted in the femoropopliteal position crossing the knee joint. All patients underwent surgery because of limb threatening ischemia (rest pain or gangrene). There was one early graft failure (successful thrombectomy). No patient died postoperatively. The mean follow-up period was 17.32 months (range 3-44 months). Cumulative patency rate for this follow-up period was 73%. Absence of kinking when bending the knee joint was determined by ankle Doppler pressure measurements and arteriography. If an adequate saphenous vein is not available for knee-crossing femoropopliteal bypass, externally supported PTFE can be used, yielding short-term patency rates comparable to those obtained with autologous venous bypasses.     

Seven-year follow-up of expanded polytetrafluoroethylene (PTFE) femoropopliteal bypass grafts.

Expanded polytetrafluoroethylene (PTFE) grafts have proven to be an acceptable short-term alternative for femoropopliteal reconstruction in those patients without suitable autologous saphenous vein. One hundred and twenty-seven femoropopliteal arterial bypass operations utilizing PTFE grafts were performed in 105 patients. Seven-year follow-up is now available for 20 grafts, 6-year follow-up for 47 grafts, and 5-year follow-up for 62 grafts. Graft occlusion was determined by angiography, Doppler assessment, loss of previously palpable pulses, or return of symptoms. Thirty nonocclusive graft losses were due to death, infection, aneurysm, amputation, or proximal occlusive disease. Overall cumulative patency rate, according to occlusive criteria alone and calculated by the life-table method, was 74% at 6 months, 63% at 1 year, 48% at 3 years, 40% at 5 years, and 35% at 7 years. Excluding early bypass failures (less than 1 year patency), 75% of grafts were patent at 3 years, 63% at 5 years, and 55% patent 7 years following operation. Diabetes mellitus was associated with a significantly lower patency rate. Patency rates were not adversely affected by graft diameter, distal popliteal anastomotic site, number of patent runoff vessels, preoperative symptoms, or prior arterial reconstruction. In patients without suitable autologous saphenous vein, the PTFE graft has proven to be a durable and dependable long-term alternative for femoropopliteal reconstruction.     

Expanded microporous polytetrafluoroethylene (PTFE) grafts in contaminated wounds: experimental and clinical study

Autogenous vein graft is regarded as an ideal arterial substitute for its long-term patency and relative resistance to infection. A clinical instance of life-threatening hemorrhage from an infected disrupted vein graft stimulated a study in dogs, comparing vein and PTFE graft performance in wounds contaminated with S. aureus and E. coli cultured from the patient's wound. Infective disruption of vein wall occurred in three of ten animals resulting in exsanguination and death. Host artery disruption at PTFE suture line occurred in one of ten animals. Thrombosis of graft and host artery in this animal precluded hemorrhage and death. This led to favorable clinical experiences with PTFE grafts in contaminated wounds of 22 trauma patients. It is concluded that PTFE is better assurance against disruption and hemorrhage than vein graft in contaminated, potentially infected sites. PTFE may be used preferentially as a vascular substitute in trauma patients provided that all traditional surgical safeguards and principles are followed.     

Comparison of expanded PTFE and vein grafts in lower extremity arterial reconstructions

Polytetrafluoroethylene (PTFE) bypasses were used in a series of arterial reconstructions to the popliteal artery (45) and to arteries below that level (11). These were performed in high-risk situations in patients who lacked a suitable saphenous vein. Vein bypasses were performed in a comparable series of high-risk situations in patients having a suitable autologous saphenous vein (45 to the level of the popliteal artery and 11 to an artery below that level). PTFE patency rates at 4-14 months were 43 to 45 (96%) for the femoro-popliteal reconstructions (with a limb salvage rate of 39 to 45 or 87%) and 5 of 11 (45%) for the distal bypasses. Saphenous vein bypass patency rates at 8-14 months were 39 of 45 (87%) for the femoropopliteal reconstructions (with a limb salvage rate of 36 of 45 or 80%) and 5 of 11 (45%) for the distal bypasses. These results justify continued use of PTFE grafts in patients without saphenous veins who require lower extremity arterial reconstructions for limb salvage. The exact place of PTFE grafts in arterial reconstructive surgery of the lower extremity definition based on longer periods of observation.     

Reverse tapered vs. straight PTFE (Gore-Tex) grafts in dogs

Reversed Autogenous Saphenous Vein (RASV) remains the material of choice in infrainguinal arterial bypass. A characteristic of RASV not seen in other grafts is its reverse tapered (RT) configuration. The purpose of this study was to investigate this geometric configuration. Straight 6 mm PTFE (gore-tex) grafts (SG) and 4-7 mm reverse tapered PTFE (gore-tex) grafts (RTG) were both implanted in the aorto-iliac position in 16 mongrel dogs. Specimens of surviving dogs were examined by the usual methods. In terms of absolute patency, 9 of 14 RTG (64%) and 5 of 14 SG (36%) P = 0.05, anastomotic thrombus formation 6 of 14 (43%) RTG vs. 10 of 14 (71%) SG P = 0.05 and in midgraft thrombus deposition P = 0.025 the RTG performed significantly better than the SG. In light of these results and other considerations, the reverse tapered configuration merits clinical investigation with other materials and in other species.     

Long-term histological changes in 1 millimeter polytetrafluoroethylene (Gore-Tex) prosthetic arterial grafts

Vein grafts are used extensively to repair blood vessels. However, when suitable vein segments are unavailable, alternative graft materials must be used. This study tested the suitability of 1 mm diameter polytetrafluoroethylene (PTFE) grafts for small-calibre arterial replacements. Grafts of 4 mm length were inserted microsurgically into the iliac arteries of 26 rats. The grafts were removed between 3 and 22 months postoperatively and examined with light microscopy and scanning and transmission electron microscopy (SEM:TEM). Anastomotic intimal hyperplasia was minimal, consisting of a few smooth muscle cells extending 100-200 microns onto the graft. The rest of the PTFE was covered with endothelium. In a few isolated areas, there was a subendothelial layer of smooth muscle, 2-10 cells thick. The short segments used in this study were highly successful, with an overall long-term patency rate of 80%. These grafts showed no evidence of excessive neo-intimal hyperplasia.     

Expanded PTFE (polytetrafluoroethylene) vascular prostheses--a new path of arterial and venous replacement]

Based on existing experimental and clinical observations the expanded PTFE graft shows convincing advantages in some indication fields (e.g., vascular access for hemodialysis, venous reconstruction) compared with conventional porous prostheses and biografts. On the other hand, we have to realize that expanded PTFE is not yet qualified to be the optimal substitute for small arteries. In spite of encouraging preliminary results, the use of this new type of vascular prosthesis still requires critical evaluation to avoid unpredictable failure due to uncritical surgical optimism (caution: Sparks disaster!). Further improvements may be expected from a better anchorage in the surrounding tissue (e.g., external velour), and from an increase of antithrombogenity of the inner surface.     

Regeneration of endothelium in knitted and velour dacron vascular grafts in dogs

Velour Dacron vascular grafts have been developed for clinical use because previous investigations of conventional fabric grafts in animals suggested that fibroblastic ingrowth contributed directly to neoendothelialization. In order to determine whether fibroblastic ingrowth was casually related to regeneration of endothelium in velour grafts, composite grafts of knitted and velour Dacron were used to replace either the carotid arteries or the abdominal aorta in 12 adult dogs and were studied by scanning electron microscopy and light microscopy. Partial or complete endothelialization occurred in all aortic grafts. Regeneration of endothelium was identified in three of six carotid velour grafts but was not observed in carotid knitted grafts. although velour grafts stimulated more aggressive perigraft fibrosis in both carotid and aortic replacement than did knitted grafts, transmural migration of fibroblasts from perigraft tissues was not observed in any specimen. The results of this study do not support a causal relationship between fibroblastic ingrowth and regeneration of endothelium in dogs.     

Clinical experience with expanded polytetrafluoroethylene (Gore-Tex) grafts for femoropopliteal arterial bypass

Thirty-seven grafts of expanded polytetrafluo-roethylene were implanted in 28 patients in whom autogeneous saphenous vein was not available, either for symptoms of severe claudication or limb salvage. The length of follow-up ranges from 8 to 28 months. The patency rate is 86.9 percent for the patients with severe claudication and 71.4 percent in the limb salvage group; the overall patency rate is 81 percent. We believe that expanded polytetrafluoroethylene is a good prosthetic substitute when autogenous vein is unavailable.     

An evaluation of expanded polytetrafluoroethylene (PTFE) loop grafts in the thigh as vascular access for haemodialysis in patients with access problems.

A total of 21 patients with vascular access problems received 22 PTFE loop grafts in the thigh as vascular access for haemodialysis. Eighteen of 22 grafts supported haemodialysis during the patients' lifetime. Actuarial patient survival was 50% at 2 years with a cumulative graft patency in the survivors of 80.5%. Although early thrombosis has been a problem, no graft has been lost from infection. We feel that these results are encouraging enough to recommend the use of PTFE grafts in the thigh of patients with vascular access problems.