A small arterial substitute: expanded microporous polytetrafluoroethylene: patency versus porosity

One hundred percent patency of one-millimeter polytetrafluoroethylene (Gore-tex) grafts in the carotid arteries of rats

Expanded polytetrafluoroethylene arterial interposition grafts with an internal diameter of 1.0 mm were placed in the carotid arteries of rats. At 2 weeks, 100% patency rate was achieved by the use of strict sterile technique in 23 rats. In contrast, only 1 out of 21 grafts remained open in rats operated using standard clean but nonsterile technique, 5% patency. All thrombosed grafts showed evidence of infection. Orally administered aspirin at therapeutic doses prolonged bleeding times in the rats but did not affect patency results in either group.

An effective sleeving technique in nerve repair

This report describes the use of a porous polymeric sleeve (Gore-tex) to direct nerve fiber growth after axotomy. Select nerves of the triceps surae muscles in 5 adult cats were surgically isolated, sectioned, and crossed or self- reunited . A piece of Gore-tex, 15 mm in length, was compressed to 5 mm and sleeved over each distal nerve end. The appropriate proximal and distal ends were stitched together, and the Gore-tex stretched back to its original length over the suture junction. The effectiveness of the Gore-tex sleeve was assessed 4-15 months post-operatively. Electrophysiological measurements of muscle force and dorsal root volleys revealed a complete absence of unintended reinnervation and a regeneration that was more substantial for motor than sensory axons. Finally, serial histological cross-sections were prepared for each nerve above, below and at the cross union. There was no evidence of nerve tissue invading the Gore-tex wall.

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.

Macromolecular, histological, ultrastructural and immunocytochemical characteristics of the neointima developed within PTFE vascular grafts. Experimental study in dogs

The nature and characteristics of the tissue that develops on the inner surfaces of vascular arterial PTFE prostheses have been investigated by histological, morphometrical, ultrastructural, and immunocytochemical criteria. The ability of this tissue to synthetize glycoproteins and glycosamino-glycuronoglycans (previously called mucopolysaccharides) has been compared to that of the normal arterial wall. PTFE prostheses were used for carotid replacement in the dog and studied until the 90th postoperative day. These prostheses were mainly characterized by (1) a limited or even absent neointimal tissue proliferation; (2) the absence of an endothelial-like structure on the prosthesis using scanning electron microscopy and immunocytochemical staining with rabbit antidog factor VIII-related antigen sera; (3) limited activities of both microsomial enzymes (sialyl transferase and N-acetyl-glucosaminyl-transferase) but marked xylosyl transferase activity; and (4) inverse qualitative distribution of the glycosaminoglycans, i.e., decrease of heparan sulfate and chondroitin-6-sulfate and increase of hyaluronic acid and dermatan sulfate. The absence of morphological evidence of an endothelial structure at the blood--prosthesis interface even 3 months after implantation and the marked functional impairment in the biosynthesis of macromolecular components responsible for the normal blood--vessel interface suggest that this newly developed tissue cannot be considered a true vascular endothelium.

A novel process for the manufacturing of porous grafts: process description and product evaluation

A novel process has been developed for the manufacture of porous vascular grafts from solutions or melts of polymers. It allows the manufacture of grafts with controllable porosity, pore size, and mechanical properties. In this process, the polymer melt or polymer solution is extruded through fine orifices; the fibers are then stretched and wound on a rotating mandril. Fiber-fiber bonding takes place, resulting in the formation of stable porous tubes. The effects of the process variables on the physical properties of the resulting graft have been studied and preliminary in vivo evaluation in dogs has demonstrated graft patency with a thin, stable neointima in both small (4 mm) and large (10 mm) caliber configurations.

Evaluation of the patency rate of fibrous microvascular polyurethane prostheses after implantation in the rat aorta

Two types of fibrous polyurethane prostheses with different compliances were implanted into the rat aorta with interrupted sutures and a running suture line. Excluding two technical failures, one unexplained death, and three infected prostheses, both groups (n = 21) showed a patency rate of 100%, up to 6 months after implantation. Rapid reendothelialisation occurred, and a stable neo-intima was formed. Compliance of the prostheses, as well as the suture technique used, has proven to be an unimportant factor in the rat aorta model, probably due to the low magnitude of the pulsations of the rat aorta. The experience of the surgeon with microsurgical techniques seems to be an underestimated factor in determining patency rates of microvascular prostheses.

A new in vivo model of arterial thrombosis: the effect of administration of ticlopidine and verapamil in dogs

An in vivo model of arterial thrombosis was developed in which either polytetrafluoroethylene (PTFE [Gore-Tex]) or autologous vein grafts were used to replace a segment of the femoral arteries of dogs. In one series of studies, 5 cm of PTFE and 5 cm of autologous femoral vein were used in each animal and blood flow was resumed for 1 hour. 111In-labeled autologous platelets accumulated in greater amounts on the PTFE grafts (93.6 X 10(6) platelets/cm) than on the vein grafts (2.6 X 10(6) platelets/cm) (P less than 0.001). Orally administered ticlopidine (30 mg/kg/day for 2 days), an established inhibitor of platelets, reduced platelet deposition on the PTFE grafts to 10.5 X 10(6) platelets/cm (P less than 0.01). In a second series of studies, PTFE grafts were interposed on both sides in each animal, and blood flow was resumed for 3 hours. With intravenously administered verapamil, a calcium antagonist, given perioperatively at 7.5 ug/kg/min, 12 of 16 grafts in eight dogs were patent compared with only 2 of 16 grafts in eight control dogs (P less than 0.001). Furthermore, platelet deposition on the grafts was reduced from 1,090 X 10(6) platelets/cm to 303 X 10(6) platelets/cm (P less than 0.001). Thus, both ticlopidine and verapamil are effective antithrombotic agents as a result of their inhibition of platelet activity in this model, and these results provide further evidence of a central role for calcium in platelet activation.

A study of the interface between a fibrous polyurethane arterial prosthesis and natural tissue

Fibrous polyurethane samples were implanted in subcutaneous tissue, muscle, and as an arterial prosthesis for periods up to six months. The interface between the polymer and living tissue was studied using optical, scanning, and transmission electron microscopy. A good correlation was found between the micromorphology of the polymer-tissue interface observed in three experimental methods used. Ingrowth of tissue occurs by cell penetration into the fibrous network of the polymer implant and eventual encapsulation by connective tissue. Full details of the distribution of collagen and the cell components around the individual polymer fibers and the structure of the connective tissue are given.

Ureteral replacement with a new synthetic material: Gore-Tex

There are no currently accepted synthetic ureteral substitutes. When faced with the need for ureteral replacement, the urologist must resort to pedicle grafts of intestine or bladder. Based on encouraging preliminary work in Europe, we have used a new synthetic vascular substitute, Gore-Tex, to replace segments of ureter in the dog. This material is made of expanded (microporous) polytetrafluoroethylene. In vascular surgery it is currently the preferred material due to its non-wetting and non-clotting surface when used in the arterial and venous beds. Adult mongrel dogs underwent segmental replacement of the right ureter and subtotal replacement of the left ureter with segments of 5-mm. tubed Gore-Tex. All anastomoses were performed with running 6--0 prolene. Antibiotics were given routinely perioperatively. Data on 7 dogs are available. Results indicate that Gore-Tex is well tolerated as a ureteral substitute to bridge gaps between segments of ureter. Anastomoses of Gore-Tex to bladder were not successful, resulting in infection and migration of the prosthesis. Under proper circumstances, Gore-Tex can be a useful potential addition to the urologic armamentarium.

Current PTFE grafts: a biomechanical, scanning electron, and light microscopic evaluation

Two currently available brands of PTFE grafts (Goretex and Impra) were studied in a canine femoral artery model to determine whether changes in the manufacturing processes of the two grafts, which increased their strength, had altered the biophysical properties and the histological reactivity of either graft. Both grafts were found to be similar except for differences in their suturability. Their in vivo dynamic compliances were almost identical (1.2 +/- 0.35 vs. 1.2 +/- 0.45). (Scanning electron microscopy showed endothelialization of the grafts only adjacent to the anastomoses, and light microscopy demonstrated similar degrees of histologic incorporation by the host tissues, though of slower tempo than that previously described. These results are examined and discussed with regard to the suitability of this model for characterizing new arterial prostheses of small to medium diameter.

Glutaraldehyde tanned ovine collagen compared with polytetrafluoroethylene (Gore-Tex) as a conduit for small calibre artery substitution; an experimental study in dogs

Collagen tubes with a polyester mesh endoskeleton were grown in sheep around silastic mandrils and were then tanned in alkaline glutaraldehyde. Tanned ovine collagen conduits and polytetrafluoroethylene conduits (Gore-Tex), each 10 cm long and 6 mm wide, were deployed in parallel as aorto-iliac bypass grafts in 10 dogs. The grafts remained patent for periods up to and exceeding 23 months. No grafts showed aneurysmal dilatation. All grafts formed a neointima lined with cells. In the Gore-Tex grafts there was fibrous tissue ingrowth through the wall which resulted in progressive and irregular luminal narrowing. This was not seen in the tanned ovine collagen grafts.

Aortocoronary Gore-Tex graft: 18-month patency

Despite widespread success with Gore-Tex (polytetrafluoroethylene) vascular grafts in peripheral artery operations, very little use has been made of this material in aortocoronary bypasses. We present the case of a 61-year-old woman with a 6-month history of angina who was found to have no suitable saphenous vein available at operation and who therefore underwent Gore-Tex bypass grafting to the right coronary artery. Coronary angiograms made 6 months and 18 months postoperatively showed patency of the 6 mm Gore-Tex replacement graft as well as the internal mammary artery placed to the left anterior descending coronary artery. Although frequent follow-up and close observation are recommended in patients with aortocoronary Gore-Tex grafting, the unique design of this material has made it the best alternative for synthetic coronary bypass conduit in the absence of the saphenous veins, particularly when these veins are found to be inadequate only at the time of operation.

Expanded polytetrafluoroethylene grafts for severe lower limb ischaemia

Three years' experience with the use of expanded polytetrafluoroethylene grafts for severe lower extremity ischaemia are reported; 44 femoropopliteal bypasses were performed, 35 for limb salvage. The prosthesis was used when no saphenous vein was available (23) or to shorten operation time in infirm patients (21). Of 41 patients with a mean age of 70 years, 19 had significant ischaemic heart disease and 10 were diabetic. The mean follow-up period for patient grafts is now 16 months (4--39 months), and the overall life-table cumulative patency is 59 per cent at 6 months, 52 per cent at 1 year and 40 per cent at 2 years. No correlation was demonstrated between patency and run-off, diabetes or smoking, but above-knee grafts may do better than those below the knee. Twenty grafts have occluded leading to 12 amputations, 3 further reconstructions and 1 death. Nine other deaths have occurred from causes not directly related to the lower limb ischaemia, 4 perioperatively and 5 later. The graft described were used in elderly unfit patients, most of whom would have had amputations before the introduction of polytetrafluoroethylene grafts. The results presented support the continued evaluation of this prosthesis in such selected cases.

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.

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.

Postoperative angiographic assessment of modified Blalock-Taussig shunts using expanded polytetrafluoroethylene (Gore-Tex)

Thirty-six of 87 modified Blalock-Taussig shunts done with expanded polytetrafluoroethylene (Gore-Tex) were restudied angiocardiographically. In 7 patients the study was carried out within 1 month of the shunt operation because the patients failed to make satisfactory clinical progress. Two shunts were occluded and 1 ws stenosed; all 3 were in neonates. The remaining 29 patients were reinvestigated electively between 5 and 29 months postoperatively and had a 97% shunt patency rate. Because of the rather high incidence of irregular or stenosed shunts among neonates with 4 mm conduits, we now prefer to use a larger conduit even in this age group.

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.

Femoropopliteal bypass using polytetrafluoroethylene

Reinforced expanded polytetrafluoroethylene (PTFE) was used as a femoropopliteal bypass graft in 31 patients (37 operations). The indications were intermittent claudication (13 operations), severe ischaemia with rest pain or gangrene (20 operations), and prophylactic treatment of popliteal aneurysms (4 operations). The one-year accumulative patency rates were 75% for patients with intermittent claudication and 20% for patients with severe ischaemia. In three patients with claudication, graft thrombosis led to amputation in spite of attempted graft thrombectomy. These results compare unfavourably with our experience using autogenous vein, in which the one-year accumulative patency rates were 80% for claudication and 70% for severe ischaemia, and in which failure of the bypass graft for claudication rarely made the patient worse.

Fibrocollagenous tissue tube as a small arterial substitute

A new arterial graft, a fibrocollagenous tissue tube supported by polyester mesh, was evaluated as a substitute for a small caliber artery. The graft of 3 mm in internal diameter and 3.5 to 5.7 cm in length were implanted into the external iliac arteries of 24 dogs. The patency rate of the graft was 73% from 0 to 7 months following the operation. The newly formed vascular wall was soft and stable. The graft showed good endothelization of the neointima.

Small artery reconstruction with a new vascular prosthesis

In the Surgical Department of the University of Erlangen, 307 reconstructions in all areas of the arterial tree were performed with PTFE (GORE-TEX) grafts, of which 188 were performed in the femoral-popliteal and femoral-crural areas. Femoral-popliteal bypass grafts above the knee joint remained patent in 93% of the patients during an average follow-up time of 6.7 months. Below the knee joint, the patency rate was 85% during an average follow-up time of 5.6 months. In the proximal aorta, aorta-renal, and aorta-femoral areas, long-term results with the PTFE graft have been excellent.

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

Thirty-seven grafts of expanded polytetrafluoroethylene 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.

The prosthetic (Teflon) central aortopulmonary shunt for cyanotic infants less than three weeks old: results and long-term follow-up

The expanded microporous polytetrafluoroethylene (PTFE) 4 mm vascular prosthesis has been used to create a central aortopulmonary shunt in 20 critically ill infants less than 3 weeks old. The infants ranged from 1 to 18 days old (5.25 days), and from 1.5 to 4.0 kg (2.9 kg). Conduit length ranged from 2 to 6 cm (4 cm). Sixteen patients had atresia of the tricuspid or pulmonary valve. There were 6 early deaths (30%), only 1 of which was shunt related. The mean preoperative arterial oxygen saturation was 62% (range, 33 to 80%), and mean postoperative saturation was 87% (range, 78 to 90%). There were 5 late deaths, 1 probably caused by shunt failure. Nine long-term survivors have done well. Follow-up ranges from 1 to 36 months (18 months). Factors influencing conduit function are length, technical considerations, and pulmonary vascular resistance. Late restudy in 5 of 9 survivors confirms patency and demonstrates bidirectional pulmonary blood flow. Since PTFE shunt flow capability is fixed, the infant may require repair or a second shunt within 24 months of the initial procedure.

PTFE (Goretex) femoropopliteal reconstruction for limb salvage

We present the results of the use of polytetrafluoroethylene (PTFE, Goretex) grafts for limb salvage in 20 cases of femoropopliteal or more distal arterial reconstruction. There appears to be no relationship between graft survival and 'run-off' or the overall disease state of the vessels. Cumulative graft patency was almost 50% at 6 months, which is in contrast with higher patency rates reported from other countries.

Expanded polytetrafluoroethylene grafts for small artery replacement

Twenty vascular grafts of expanded polytetrafluoroethylene with a 1.5 mm. internal diameter and a 4.0 cm. length, were placed in the femoral arteries of dogs. The animals, divided into two groups, with and without pluronic F 68, were sacrificed two weeks after surgery. The patency rate was 33.3% (2/6) and 21.5% (3/14), which was not statistically significant. One factor contributing to the occlusion of the grafts were excessive proliferation of granulation tissue due to early formation of the thrombus. Histological findings showed that the pseudointima was almost complete, although it was only about 0.114 mm. thick at the anastomotic line.

Aorta-pulmonary artery shunts with expanded polytetrafluoroethylene (PTFE) tube

Ten patients underwent an aortapulmonary artery shunt with a polytetrafluoroethylene (PTFE) tube between December, 1976, and October, 1977. Five of them were less than 1 month old. The diameter of the PTFE tube was 5 mm in 9 patients and 4 mm in 1 patient. Seven patients survived the operation. One of them had a clotted shunt, which was reoperated on successfully. Three patients died in the postoperative period, and all had a patent shunt. Overall patency was 90% (9/10). Congestive heart failure refractory to medical treatment developed in 1 patient with a patent Blalock-Taussig and PTFE shunt. In our institution, the Blalock-Taussig shunt is the procedure of choice. The PTFE shunt is used when the anatomy of a patient is unsuitable for a Blalock-Taussig shunt. A tube diameter of 5 mm is optimal for infants when further growth is considered, even if digitalization is necessary to control congestive heart failure.

Arterial reconstruction with polytetrafluoroethylene: a preliminary report

Early results of arterial reconstruction with reinforced expanded polytetrafluoroethylene (PTFE) in the lower extremity have been obtained by reviewing 55 patients undergoing 59 operations - 38 femoropopliteal bypasses and 21 long bypasses distal to the popliteal artery. The one-year accumulated patency rates were 73% for the femoropopliteal bypass group and 50% for the long bypass group. Early results suggest that PTFE is superior to Dacron and is an acceptable substitute for autogenous saphenous vein when the latter is unavailable or of inadequate calibre.

Alloplastic replacement of the partially resected canine urethra by expanded polytetrafluoroethylene grafts. Preliminary results

In 12 male dogs 3-8 cm of the penile urethra were resected and replaced by expanded polytetrafluoroethylene (GORE-TEX) grafts. Follow-up consisted of periodic urethrograms. Maximum observation time has been 12 months. Up to now, no major complications were noted. Tissue reactions were minimal and patency of all grafts was demonstrated during the follow-up period.

Changes in the manufacture of expanded microporous polytetrafluoroethylene: effects on patency and histological behavior when used to replace the superior vena cava

Polytetrafluoroethylene (PTFE) has been used clinically and experimentally as a vein substitute. Since its introduction, changes have been made in the manufacture of the material. This study was designed to evaluate the effects of pore size (fibril length), PTFE cover, and spiral tube support on long-term patency and histological behavior when this material is used as a replacement for the precava in the dog. A graft of 30-mu pore size has adequate fibroblastic ingrowth, a neointima of 200 mu or less, and the best long-term patency. The PTFE cover results in less fibroblastic involvement of the prosthetic graft and prevents late occlusion caused by transmural fibrosis in the 90-mu graft. The spiral support does not affect patency and may be indicated when external pressure on the tube must be avoided.

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.

Evaluation of the thrombogenic potential of three types of arterial graft studied in an artificial circulation

The thrombogenic potential of woven Dacron, expanded polytetrafluoroethylene (Gore-Tex) and gluteraldehyde-treated human femoral artery (HFA) grafts was evaluated using an artificial circulation. The differences in the platelet parameters (platelet count, adhesion and aggregation) and scanning electron microscopy (SEM) appearances before and after perfusion were used as indices of thrombogenicity. Platelet counts fell significantly with woven Dacron, moderately with HFA and no fall was observed with Gore-Tex. Platelet aggregation was unaffected by any graft, but platelet retention was significantly marked in woven dacron. SEM studies revealed minimal adherence of platelets to Gore-Tex and HFA endothelium, but marked adherences to woven Dacron, accompanied by morphological changes of the adhered platelets. In an artificial circulation, of the three types of arterial graft, woven Dacron has the greatest influence on platelet function, indicating significant thrombogenicity, whereas HFA is intermediate in its effect and Gore-Tex appears to have the lowest thrombogenic potential.

Reinforced expanded polytetrafluoroethylene (Gore-Tex) grafts for haemodialysis

Twenty-five vascular grafts made of expanded reinforced polytetrafluoroethylene (PTFE) were inserted as arteriovenous fistulae in 20 patients requiring intermittent haemodialysis. Thirteen grafts were placed in the forearm, either as a looped or straight configuration, and 12 straight grafts were placed in the thigh. Whereas only 45% of the forearm grafts functioned adequately, 92% of the thigh grafts supported haemodialysis satisfactorily. It is suggested that when a vascular graft for haemodialysis is required, then an arteriovenous connection of expanded PTFE placed in the thigh achieves reasonable success.

Radiographic assessment of leaflet motion of Gore-Tex laminate trileaflet valves and Hancock xenograft in tricuspid position of dogs

Six samples of various thicknessess of Gore-Tex compounds were fashioned into trileaflet valves. A radiopaque marker was placed on the center of the free margin of each cusp, and the prostheses were implanted in the tricuspid position of dogs. Two Hancock valves were studied for comparison. Catheterization revealed that the hemodynamic function was normal in all valves tested. High-speed radiography permitted analysis of leaflet movement throughout the cardiac cycle. Of the six Gore-Tex valves, five opened completely. The cusps of these five valves were fabricated from 4, 6, 8, 10, and 12 layers of Gore-Tex film. The remaining valve, which was fabricated from 15 layers of Gore-Tex film, and both porcine xenograft aortic valves did not open completely. We postulate that the laminates of 12 layers or less of Gore-Tex film are suitable for further study to evaluate their potential applicability in trileaflet cardiac valve prostheses.

Gore-Tex grafts for replacement of the superior vena cava

In an effort to evaluate polytetrafluoroethylene (Gore-Tex) as a replacement for large veins, tubular grafts of the material were substituted for the precava in 33 mongrel dogs weighing 15 to 30 kg. Thirteen dogs had grafts 10 cm long by 12 mm wide with a 15-to 30 micron pore size; 15 dogs had grafts of the same length and width from 90-micron pore size material; and 5 dogs had grafts 5 cm long by 12 mm wide, of 90-micron pore size Gore-Tex. The effect of Gore-Tex tubes with and without spiral support and the differences in anatomical positions of the grafts were evaluated in terms of patency. Dogs were killed if a venogram showed occlusion of the graft. Twelve dogs survived 90 days; the longest survivor was killed at eleven months. At postmortem examination, the graft was patent but extremely narrow at the atrial end. Modification in the fabrication of Gore-Tex may eliminate factors contributing to graft failure; experiments longer than 90 days are necessary to evaluate Gore-Tex as a large vein replacement material. The 90-micron pore size material used in this experiment was unsuitable as a canine venous substitute.