Expanded microporous polytetrafluoroethylene as canine arterial bypass or replacement graft

Expanded microporous polytetrafluoroethylene (PTFE) has been used experimentally and clinically for small-vessel bypass or replacement grafting; the results vary widely. This study assessed short (4--cm) femoral and carotid artery replacement PTFE grafts and longer (12--cm) femoral artery bypass PTFE grafts that crossed a flexion crease. Pore size at the blood-graft interface ranged from 10 to 30 mu. At the end of three months, overall patency rate was 22%. No long bypass grafts remained patent. The pore size and type of anastomosis did not affect patency. The occlusion was always thrombotic, associated with fibrin at the suture line. Nine of the 20 short carotid grafts (45%) and five of 22 short femoral grafts (22%) remained patent. These poor results indicate that further experimental studies are needed before PTFE is used clinically when an alternative exists.     

Expanded microporous polytetrafluoroethylene as a vascular substitute: a two year follow-up.

Since 1974, 131 femoropopliteal, distal popliteal, and tibial bypasses have been performed using expanded microporous polytetrafluoroethylene (PTFE). Forty patients were operated on for limb salvage, and 21 had had previous bypass procedures. The overall patency rate was 82%. Early occlusions possibly were related to technical error, but most probably were due to severity of disease and poor runoff. Late occlusions were related to progressive atherosclerosis in the proximal or distal arterial tree. A 75.7% cumulative patency rate was noted at 28 months. In man the PTFE prosthesis demonstrates a smooth intimal lining with fibroblastic ingrowth into the interstices of the graft. These results are considered to be excellent in this high-risk patient population. The patency rates achieved with PTFE are better than those accomplished with alternative conduits and approach the patency rates reported with autogenous saphenous vein. Expanded microporous polytetrafluoroethylene with its high patency, pliability, and tissue incorporation is an excellent arterial substitute. Only with continued use of this material and a more uniform patient selection can more equitable comparisons be made between expanded PTFE and the autogenous vein.     

The use of long synthetic microvascular grafts to vascularise free flaps in rabbits

A 5 cm length of 2 mm internal diameter (i.d.) synthetic, expanded polytetrafluoroethylene (PTFE, or Gore-Tex) vascular graft was used to connect 25 rabbit inferior epigastric flaps to the contralateral femoral vessels. In 15 animals an expanded PTFE graft connected the opposite femoral artery to the flap while the ipsilateral venous drainage remained intact. In the remaining 10 animals an expanded PTFE graft was used to replace the venous drainage of the flap and connected to the opposite femoral vein while the ipsilateral femoral artery supplied the flap. Flap survival and graft patency were evaluated over 3 weeks. Ten of 15 flaps with intra-arterial grafts survived at 3 weeks (67%). Only 27% (4/15) of their supplying grafts remained patent for 3 weeks, although 67% (10/15) were patent at 10 days. All 10 flaps, where expanded PTFE grafts replaced venous outflow, failed within 36 hours. At exploration these grafts were thrombosed or collapsed. In conclusion, currently available 2 mm (i.d.) expanded PTFE vascular graft cannot maintain patency in a low blood flow circulation supplying an isolated free flap.     

Experimental and clinical use of polytetrafluoroethylene vascular grafts

Synthetic textiles, saphenous veins and now expanded polytetrafluoroethylene (PTFE) allow the surgeon a wide range of vascular operations. Two sets of studies are reported testing PTFE under a variety of circumstances. Twenty-four dogs underwent either replacement of a segment of the abdominal aorta or aortoiliac bypass with PTFE or Dacron grafts. PTFE was the easiest to use and to suture. Patency was better (six of seven versus four of seven) although not statistically significant, and microscopic examination showed better tissue ingrowth and less inflammatory and fibrous reaction than the woven or knitted grafts. Twenty-two PTFE grafts (6 mm in internal diameter) were implanted in 19 patients for use as vascular access during hemodialysis. All patients presented with damaged blood vessels and had undergone multiple vascular access procedures previously. Graft patency was excellent (three grafts were removed because of infection, vascular steal or occlusion and three grafts were revised because of obstruction or bleeding); the grafts allowed good flows during dialysis and they were easy and convenient to implant. PTFE tolerates pressure and flows in medium and large arteries, its patency rate is excellent, it is easy to use, and its interactions with tissues are adequate.     

Segmental Uterine Horn Replacement in the Rat Using a Biodegradable Microporous Synthetic Tube

To investigate the possible use of a biodegradable microporous synthetic tube for fallopian tube replacement, polyetherurethane/poly-L-lactide (PU/PLLA) grafts in the uterine horn of the rat were studied and their patency and healing characteristics compared with those of nonbiodegradable polytetrafluoroethylene (PTFE; Teflon) grafts as well as with those of reanastomosed uterine horns. Regarding the healing characteristics, the PU/PLLA grafts were superior to the PTFE graft, as was indicated by the regeneration of endometrium and the extensive perigraft tissue ingrowth. However, the graft/uterine anastomoses of the PU/PLLA and PTFE grafts became obstructed by a plug of mucosal folds, all reanastomosed, uterine horns in the control experiments remaining open. In conclusion, although biodegradable microporous PU/PLLA uterine horn grafts have better healing characteristics than PTFE grafts, they easily obstruct at the graft/uterine junction. Mucosal suturing and/or the use of splints may contribute to the feasibility of biodegradable microporous artificial fallopian tubes in tubal surgery.     

The use of expanded microporous polytetrafluoroethylene for limb salvage: a preliminary report.

Initial laboratory and clinical evaluations of a new prosthetic material, expanded microporous polytetrafluoroethylene (PTFE), for small vessel replacement is promising and encourages further clinical trial. Frequently the autogenous saphenous vein is not available for bypass procedures, and alternative arterial substitutes have not proved reliable for replacement of small vessels. In this study, 15 patients with impending loss of limb and no available saphenous vein underwent revascularization of the lower extremity with expanded microporous PTFE grafts. Thirteen of 15 patients now demonstrate viable extremities with a resulting over-all early patency and limb salvage rate of 87 percent for this series. Follow-up ranges from one to 8 months. Seven patients had diabetes mellitus and eight had atherosclerotic heart disease. Nine grafts crossed the knee joint. In all patients arterial runoff was poor. Six patients had previous femoropopliteal bypasses, five with autogenous veins and one with Dacron velour. Two patients had multiple previous operations that failed, first with autogenous vein and later with fabric grafts. The current limb salvage and patency rate of 87 percent in high-risk patients suggests that expanded PTFE may be the prosthesis of choice when an autogenous vein is not available and possibly an equally good substitute when the venous autograft is available.     

Microarterial prostheses of expanded polytetrafluoroethylene

Forty grafts of expanded polytetrafluoroethylene (PTFE) with an inside diameter of 1.5 mm were placed in the femoral arteries of rabbits. The telescoped technique was used for the anastomoses. The animals were sacrificed at intervals beginning the day after implantation. Four of the grafts lost patency and one graft had a remarkable degree of intimal hypertrophy. The remaining grafts developed thin neointimal formations and remained patent up to 7 months after implantation. The overall patency rate was 90%. Neointimization was established 35 to 90 days following surgery. The formation of neointima began at the anastomotic sites and extended into the grafts. It is concluded that PTFE prostheses can be used for grafting arteries as small as 1.0-1.2 mm in diameter, which up to now had been considered impossible.     

Nerve regeneration through a synthetic microporous tube (expanded polytetrafluoroethylene): experimental study in the sciatic nerve of the rat

Nerve grafts made of expanded polytetrafluoroethylene (PTFE) were used to bridge 10-mm gaps in the sciatic nerves of rats. The most prominent gross and histological finding was abundant neovascularization and capillary ingrowth through the microporous PTFE wall. Organized, myelinated nerve tissue was observed. After 4 months, regeneration through hollow PTFE tubes (N = 16) was equivalent to autogenous nerve grafts (N = 12) as measured by gastrocnemius muscle weights (P = 0.33). Nerve conduction velocity in the hollow PTFE tubes was 21.7 m/sec as compared to 50.6 m/sec in the control nerves (P less than 0.001).     

Expanded polytetrafluoroethylene as a microvascular graft: An experimental study

The patency rates of expanded polytetrafluoroethylene (PTFE) vascular grafts with internal diameters of 1.0–3.0 mm were evaluated in three different species (dogs, rabbits, and rats). An overall 2-week patency rate of 14 (23%) of 60 was obtained, with the exception of 10 (83%) of 12 grafts 1.8 mm in diameter inserted in the carotid arteries of rabbits. The presence of numerous variables in the structural properties of PTFE may explain the variable results reported in the literature and this study. Heparinization did not improve the results, nor did modification in suture technique. At the present time, PTFE cannot be considered an equivalent to or a substitute for autogenous vein grafts in microvascular surgery.     

Achieving better patency rates and neoendothelialization in 1-millimeter polytetrafluoroethylene grafts by varying fibril length and wall thickness.

This study evaluates the effects of different fibril lengths and wall thicknesses on patency and neoendothelialization in 1 mm inner diameter polytetrafluoroethylene (PTFE; Gore-Tex) grafts and highlights the importance of longer fibril lengths and matching wall thicknesses. Fibril lengths tested were 30, 60, and 90 microns. The grafts had a wall thickness ranging from 0.18 to 0.34 mm. Ninety-six grafts were implanted in the infrarenal aorta of Wistar rats. Grafts were harvested at various intervals and examined macroscopically, by light microscopy, and by scanning electron microscopy. Both the highest patency rates and the best grades of neoendothelialization were observed in the 90 microns fibril length grafts, while the lowest of both were seen in the 30 microns fibril length grafts. From this study we conclude that 90 microns fibril length PTFE can be considered a valid micrograft for bridging arterial defects in microvascular reconstructive procedures.     

Expanded polytetrafluoroethylene as dialysis access grafts: serial study of histology and fibrinolytic activity.

Expanded polytetrafluoroethylene (Gore-Tex) grafts were evaluated as hemodialysis access shunts. A serial study of cellular ingrowth and endothelialization was performed. The development of fibrinolytic activator was sequentially monitored and shown to be consistently higher in the Gore-Tex grafts than in either knitted or woven Dacron prostheses. Functional assessment by repeated needle puncture demonstrated that PTFE grafts were durable, had uniform patency (6 mm ID size) and showed no evidence of degeneration during the time limit of this study. Although these are favorable characteristics, further long-term evaluation of PTFE grafts is necessary before its role as a vascular prosthesis applicable to clinical practice, can be established.     

Morphologic quantitation of pseudointima and effects of antiplatelet drugs on vascular prostheses in goats

The natural process of endothelialization, pseudointimal formation, and connective tissue incorporation of the expanded PTFE grafts in the goat was documented through histologic examination of specimens harvested at 2, 4, 6, and 8 weeks. The goats demonstrated a progressive increase in pseudointimal pannus ingrowth from the anastomoses at a rate of 11.3 mm over a 12 week period. Histologic changes according to time of vascular graft incorporation in the goat model were found to be comparable to those of the dog, pig, and calf models reported in the literature. Platelet-inhibiting drugs, aspirin, dipyridamole, nifedipine, and ibuprofen were administered to goats after replacement of their infrarenal aorta with 5 cm of 8 mm diameter expanded PTFE grafts. The effects of the drugs on graft endothelialization and anastomotic pseudointimal formation was compared with those in the untreated control group after 12 weeks. Aspirin and dipyridamole had no detrimental effect on the healing process compared with the untreated control group. Studies with nifedipine and ibuprofen did not demonstrate a decrease in pseudointimal hyperplasia. Antiplatelet treatment resulted in no significant change in the rate of endothelialization of expanded PTFE grafts.     

Composite porosity of expanded polytetrafluoroethylene vascular prosthesis

Polytetrafluoroethylene (PTFE) prostheses were modified to produce two types of composite porosity PTFE grafts: type I — inner 60 μm/outer 20 μm and type II — inner 20 μm/outer 60 μm. These composite porosity PTFE designs were investigated for bleed through, graft healing and patency and compared with high porosity PTFE (60 μm) and standard PTFE (20 μm) grafts. The grafts were implanted into the carotid and femoral arteries of dogs and retrieved after 4, 12 and 18 weeks. Both composite porosity grafts showed significantly less bleed through than standard and high porosity grafts after reperfusion. In composite grafts, the 60-μm layer allowed fibrovascular tissue and histiocyte ingrowth from perigraft tissue, but the 20-μm layer did not. Neointima formation occurred earlier and endothelialization was more extensive in high porosity grafts, but seroma formation occurred in 25% of cases. In type I composite porosity grafts, smooth muscle cells of neointima migrated into the pores of the graft, providing a firmly anchored intima. Type II composite porosity grafts allowed better ingrowth of fibrovascular tissue at the outer layer from the perigraft tissue; however, endothelialization was not completed. Composite porosity grafts should be considered for evaluation in specific clinical situations.     

Bovine carotid artery and expanded polytetrafluroethylene grafts for hemodialysis vascular access

Seventy-six bovine carotid artery heterografts (BCAH) and 100 expanded polytetrafluroethylene (PTFE) grafts were inserted as chronic hemodialysis arteriovenous fistulas. Cumulative patency at 1 year was 70% for the BCAH group and 87% for the PTFE group and at 2 years was 45 and 73%, respectively. Infection accounted for 38% of BCAH failures and none of the PTFE failures. BCAH required twice as many revisions per dialysis month to maintain patency as did the PTFE grafts (0.036 vs 0.019, respectively). Graft configuration and location did not affect patency rates. At present the PTFE grafts appear superior to the BCAH for construction of arteriovenous dialysis fistulas.     

Impact of endothelial cell seeding on long-term patency and subendothelial proliferation in a small-caliber highly porous polytetrafluoroethylene graft

Previous reports have demonstrated that endothelial cell seeding of polytetrafluoroethylene (PTFE) grafts enhances short-term patency. This experiment was undertaken to study its impact on the long-term patency of a highly porous, experimental PTFE graft and to determine whether increasing the internodal distance of the graft material resulted in increased proliferation of the subendothelium. Ten centimeter long, 4 mm internal diameter segments of an unreinforced, experimental PTFE graft were implanted into 36 mongrel dogs as carotid interpositions. In each animal, one graft was seeded with autologous endothelial cells, enzymatically derived from the external jugular veins, whereas the contralateral graft was treated in identical fashion except that endothelial cells were not added to the preclot mixture. Nineteen animals were killed at 12 weeks; six at 22 weeks; eight at 26 weeks; and three at 52 weeks. The mean follow-up period was 20.1 weeks. The overall patency rate was 58.3% (21 of 36 grafts) for seeded grafts vs. 27.8% (10 of 36 grafts) for control grafts (p less than 0.01). The thrombus-free area was planimetrically measured at 83.4% +/- 4.5% in seeded grafts vs. 55.1% +/- 9.7% in control grafts (p less than 0.05). Scanning electron microscopy confirmed the presence of a confluent cellular monolayer in seeded grafts, whereas control grafts exhibited a variable coagulum of fibrin, platelets, and endothelial cells. The thickness of the subendothelial layer varied from 56 to 95 micron with no progressive increase in thickness between 12 and 52 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vivo study of an elastomer end-coated polytetrafluoroethylene vascular prosthesis.

Polyurethane end-coated polytetrafluoroethylene (PTFE) grafts (elastomer PTFE grafts) were implanted in 12 female adult mongrel dogs to assess patency, intimalization, tissue incorporation, and technical suitability of the material as a vascular graft. Each dog had bilateral aortoiliac grafts placed, one a standard PTFE and the other an elastomer PTFE graft. The length of the grafts was 7-8 cm and the diameter was 6 mm. The grafts were harvested at intervals to 120 days postoperatively. The elastomer PTFE grafts showed superior longitudinal elasticity, retention of shape, and no graft tearing with suture tension; however, no significant difference in bleeding was noted at the anastomoses between the standard and elastomer PTFE grafts. Satisfactory patency was obtained with both standard (8/10) and elastomer PTFE grafts (9/10) at 90-120 days. No significant difference in the thickness of intima and the length of pannus ingrowth was noted between the standard and elastomer PTFE grafts. No outer tissue incorporation was seen at the elastomer-treated graft segments as opposed to the well-incorporated untreated segments. In conclusion, elastomer end-coating of a PTFE vascular prosthesis provided excellent handling characteristics without detracting from patency; however, the lack of outer tissue incorporation may be a potential disadvantage in its clinical use.     

Fluoropolymer-coated dacron versus PTFE grafts for femorofemoral crossover bypass: randomised trial.

OBJECTIVES: To investigate whether patency of a thin walled 8 mm fluoropassivated Dacron graft was similar to that of a standard 8mm PTFE graft for femorofemoral crossover bypass surgery. DESIGN: A randomised multicentre clinical trial comparing two vascular grafts with participation of 10 departments of vascular surgery in Denmark, Sweden and Norway. PATIENTS AND METHODS: 198 patients were randomised to PTFE (n=107) or fluoropolymer-coated Dacron grafts (n=91), 63% underwent surgery for claudication, 27% for ischaemic rest pain and 10% for tissue loss. The median follow-up time was 24 months (IQR 19-26 months). RESULTS: The primary patency rate of the two grafts was similar (log rank test: p=0.35). The primary patency rates (95% CI) for coated Dacron and PTFE grafts were 92% (86-98) and 94% (89-99) at 12 months and 87% (74-95) and 93% (87-99) at 24 months, respectively. CONCLUSION: In patients with unilateral iliac artery disease not amenable to angioplasty, the femoral-femoral bypass is durable and effective. No difference in patency was found between the two graft materials (fluoropolymer coated Dacron and PTFE).     

Upper arm polytetrafluoroethylene grafts for dialysis access. Analysis of two different graft sizes: 6 mm and 6-8 mm

The purpose of this retrospective study was to analyze 2 sizes of expanded polytetrafluoroethylene (PTFE) upper arm grafts for dialysis: 8 millimeters, tapered to 6 mm at the arterial side, and 6 millimeters. All upper arm PTFE grafts (Gore-Tex(R)) were performed between January 1981 and April 1997. Patient characteristics, complication rate, and patency rates were compared for both kind of grafts. Five hundred and seven PTFE grafts were analyzed (183 6-mm grafts and 324 6- to 8-mm grafts). Early failure was found in 5 grafts (2.7%) in 6-mm grafts, and in 5 grafts (1.5%) in 8-mm grafts (not significant). Steal syndrome was found in 1 patient (0.5%) of the 6-mm group, and in 11 (3.4%) of the 8-mm grafts (p=0.085). The rate of late complications requiring surgical repair was 0.56 episode per graft-year in the 6-mm grafts group, and 0.33 in the 8-mm grafts (p<0.001). Primary patency rates of 6-mm grafts were 72%, 33%, and 19% at 1, 3, and 5 years; and secondary patency rates were 86%, 68%, 56%, and 44% at 1, 3, 5, and 6 years, respectively. In the 8-mm grafts group, primary patency rates were 77%, 52%, and 39% at 1, 3, and 5 years; and secondary patency rates were 92%, 84%, 73%, and 66% at 1, 3, 5, and 6 years, respectively. Comparison of patency rates of 6-mm and 8-mm grafts were statistically significant (p<0.001) for both primary and secondary curves. However, secondary survival curves were similar for both kind of grafts in a subpopulation of diabetic patients. The authors conclude that the 8-mm graft, tapered to 6 mm at the arterial side, is a dialysis graft with fewer complications and a better patency rate than grafts of 6 mm placed in the same anatomical position, at least in a population of nondiabetic patients. Steal syndrome was observed in some cases of diabetic and older patients with a large-bore graft. Thus, this kind of prosthesis should be avoided in this population. On the other hand, this is not a prospective, randomized study made with any intention for comparison. Therefore, the aforementioned conclusions must be cautiously considered.     

Healing of high-porosity polytetrafluoroethylene arterial grafts is influenced by the nature of the surrounding tissue.

The aim of this study was to determine the influence of the nature of the perigraft tissue in the healing pattern of high-porosity polytetrafluoroethylene (PTFE) vascular grafts. Nine-centimeter long segments of unreinforced experimental high-porosity (60 microns) PTFE grafts were placed as abdominal aortic interposition in mongrel dogs. Three grafts served as controls (group A); in five dogs (group B) a 25 x 25 cm piece of devascularized omentum was wrapped around the graft. In five dogs (group C) the omentum with its own vascular supply was completely wrapped around the graft. Animals were killed 4 weeks after surgery. The percentage of thrombus-free area was 31% in group A grafts, 39% in group B grafts, and 79% in group C grafts (p less than 0.01). Scanning electron microscopy showed many confluent areas of endothelium-like cells in the midportion of group C grafts, corresponding to capillary ingrowth. Transmural endothelial migration was more evident in group C grafts. We conclude that the nature of the perigraft tissue influences transmural capillary migration and the endothelialization rate of high-porosity PTFE grafts in dogs. Agents able to increase capillary formation in the perigraft tissue might improve endothelialization of vascular grafts.     

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.