Textile Teflon arterial prostheses: how successful are they?

Today the woven and knitted Teflon vascular prostheses developed over 25 years ago by Edwards are of only minor clinical interest. The literature contains a chronology of postoperative complications critical of textile Teflon as a prosthetic material, and this led to its discontinuance as a commercial product. Recent evidence from pathologic and material analyses of three grafts removed from patients after implantation for 11, 19 and 19 years, respectively, suggests that the previously reported complications were more likely to have been related to the use of silk sutures, the fraying and ravelling of the woven and weft-knitted constructions and local or systemic reactions than to degradation of the Teflon. Experimental studies of grafts implanted in the thoracic and abdominal aortas of dogs for periods of up to 6 months support these findings. Because of the apparent long-term stability of textile Teflon as an implantable material, the authors see merit in its reintroduction as a warp-knitted vascular prosthesis.     

Improved healing of small-caliber polytetrafluoroethylene vascular prostheses by increased hydrophilicity and by enlarged fibril length. An experimental study in rats.

This study was undertaken to test whether increasing the hydrophilicity of small-caliber polytetrafluoroethylene vascular prostheses by alcohol pretreatment or increasing their fibril length might improve their healing without affecting their patency. Polytetrafluoroethylene vascular prostheses (length 1 cm, inside diameter 1.2 mm) (1) with a fibril length of 30 microns (control group; n = 18), (2) pretreated with alcohol (n = 18), or (3) with a fibril length of 60 microns (n = 18) were implanted into the abdominal aorta of rats. The prostheses were evaluated by means of routine light and scanning electron microscopy during a 6-week period after implantation. All prostheses were patent at harvesting. On implantation, the control polytetrafluoroethylene vascular prostheses were only scarcely covered with platelets. At 6 weeks they had healed in a small area adjacent to the anastomoses only. In contrast, both the alcohol-pretreated polytetrafluoroethylene prostheses and the polytetrafluoroethylene prostheses with a fibril length of 60 microns were completely covered by a thin clot layer on implantation. At 6 weeks after implantation these prostheses had almost completely healed as a result of organization of the thin clot layer by ingrowth of both endothelial and smooth muscle cells. These results demonstrate that increasing hydrophilicity of polytetrafluoroethylene vascular prostheses by alcohol pretreatment or enlarging their fibril length improves their healing by induction of a thin luminal clot layer. This clot layer provides a suitable matrix for ingrowth of both endothelial and smooth muscle cells and does not lead to thromboembolic complications.     

An experimental study of eight current arterial prostheses

Eight currently used arterial prostheses with differing constructions and materials were implanted in the descending thoracic aorta of mongrel dogs. The prostheses were Gore-Tex (polytetrafluoroethylene), DeBakey Woven, Cooley Woven, Meadox Woven Double Velour, Cooley Knitted Double Velour, Microvel, Vasculour II, and Bionit II. Five series of these eight prostheses were serially implanted in heparinized subjects. During the 40 implantations, attention was focused on three major characteristics: preclotting efficiency, surgical handling characteristics, and healing. Gore-Tex is impervious to blood. The DeBakey and Cooley woven grafts are nearly so. The remaining prostheses required preclotting. The Meadox Woven Double Velour became impervious after two preclotting steps, the Cooley Knitted Double Velour and the Bionit II required three, and the Vasculour II and the Microvel required four. The surgical handling characteristics of the knitted prostheses clearly surpassed those of the DeBakey and Cooley woven and Gore-Tex prostheses. Although the Meadox Woven Double Velour prosthesis had better conformability than the nonveloured woven, the tendency of its cut edge to fray was more pronounced. Healing was much more advanced in the knitted and woven prostheses than in the Gore-Tex.     

Plasma polymerized tetrafluoroethylene/polyethylene terephthalate vascular prostheses

Tetrafluoroethylene (TFE) was discharged onto woven polyethylene terephthalate (PET) prostheses, and the PET prostheses (50 mm long) with or without TFE were implanted into canine carotid arteries and aortas. Additional controls included polytetrafluoroethylene and Dacron. Specimens were explanted after one to 12 months, photographed, and sectioned for light and scanning and transmission electron microscopy, and thrombus-free surface areas calculated by computerized planimetry. Results showed no significant patency differences among carotid or aortic groups. However, both PET carotid groups had significantly greater thrombus-free surface areas. Histologically, both PET groups appeared identical. An endothelialized neointima covered PET carotid specimens by six months, compared with three months in the aortic position, with greater pannus ingrowth in both PET groups. Plasma polymerized TFE offered no additional advantage in these long-term experiments.     

Tissue reactions around a hydroxyapatite-coated hip prosthesis: Case report of a retrieved specimen

Bone reactions were studied around a titanium, hydroxyapatite (HA)-coated Osteonics (Allendale, NJ) bipolar hip prosthesis, which was revised for severe midthigh pain 4 years after implantation. Inspection of the retrieved prosthesis using a dissecting microscope revealed scarce remnants of a coating-like material on the surface of the prosthesis; however, histology of this layer and histology of the bony side of the bone—HA interface failed to reveal any remnants of an HA coating. The interface was covered predominantly by trabecular bone, which closely followed the contour of the prosthesis, and was partly woven nonmineralized bone. At locations where mineralized bone faced the prosthesis, many small dark titanium wear particles were found. Similar particles were found in macrophages in the intertrabecular medullary space. Polyethylene wear particles were specifically located in macrophages in a soft tissue interface at more distal levels along the stem of the prosthesis. Although the observations presented in this case cannot be generalized, it clearly shows that the HA coating layer had completely disappeared after 4 years. More detailed retrieval studies and longer clinical follow-up studies are needed before a final evaluation of the behavior of HA coatings and long-term fixation of HA-coated prostheses can be made.     

Arrangement pattern of new-lining endothelial cells

New-lining endothelial cells in the neointimae of two types of synthetic vascular prostheses were examined by light- and electron microscopy. Examination was carried out at one to 846 days post implantation of the prostheses in the thoracic aortae of 57 canines. The surfaces of both types of prostheses were covered by a continuous layer of endothelial cells. The long axes of the cells were found to be parallel to the blood stream. This observation indicates that the arrangement pattern of endothelial cells in the neointimae is largely dependent on the direction of the blood stream rather than on the direction of the tension exerted on the vascular prostheses.     

Dacron arterial grafts: the influence of porosity, velour, and maturity on thrombogenicity

It has been claimed that the neointimal healing of Dacron arterial prostheses can be enhanced by increasing porosity and including both an internal and an external velour layer. To test this, 24 patients received at random either woven (USCI, DeBakey, C. R. Bard, Inc.) or more porous, double-velour, knitted (Microvel, Meadox Medicals, Inc.) Dacron aortobifemoral prostheses. Graft thrombogenicity was measured using autogenous 111In-labeled platelets shortly following surgery and 6 to 9 months later. The thrombogenicity index was defined as the mean daily rise in the ratio of emissions over the graft to emissions over a reference area (aortic arch) and is a measure of platelet deposition. At early study the mean (+/- SE) thrombogenicity index was similar in woven and knitted graft patients at 0.19 +/- 0.4 and 0.14 +/- 0.2, respectively. In both groups it was lower (P less than 0.05) 6 to 9 months later at 0.06 +/- 0.2 (woven( and 0.08 +/- 0.1 (knitted), with again no difference between materials. Although platelet survival was restored to near normal values in both groups by 6 to 9 months, only one woven graft failed to demonstrate continued platelet accumulation by gamma-imaging. Thrombogenicity in Dacron grafts diminishes in the early months of maturation but is not affected by porosity and velour. Moreover, this thrombogenicity persists beyond the period of altered platelet survival.     

Biomaterial pretreatment with ECGF to augment endothelial cell proliferation

ECGF, a polypeptide of bovine hypothalamic derivation, is the most potent endothelial cell mitogen known, with mitogenic and chemotactic effects well demonstrated in vitro on human endothelial cells. These effects are synergized by heparin. In vivo re-endothelialization of blood-contacting biomaterials may be enhanced by bonding ECGF and heparin to prosthetic surfaces. Long woven Dacron (24 mm) and woven PDS vascular prostheses were treated first with human plasma fibronectin (10 micrograms/cm2). Porcine sodium heparin (20 micrograms/cm2) was added by means of fibronectin's heparin affinity. Pure 125I-ECGF (95% alpha, 5% beta; 1 ng/cm2) was next fixed by the heparin affinity of ECGF and followed by a second heparin layer (20 micrograms/cm2) to synergize with and stabilize ECGF. 125I-ECGF adherences were determined by scintillation counts. Attachment efficiency averaged 25%. Prostheses were interposed into rabbit aortas and harvested in triplicate from 0 to 30 days to establish in vivo washout curves. After explantation, residual 125I-ECGF was eluted from prostheses, and intact ECGF was identified by SDS gel electrophoresis. Similarly prepared but nonradioiodinated Dacron and PDS prostheses were explanted after 7 days and their ECGF eluted off for in vitro activity documentation. This ECGF retained its mitogenic properties, causing a 1000% to 1200% increase in 3H-thymidine incorporation into newly synthesized DNA in test murine LE-II cells. Fibronectin-heparin-ECGF fixation to blood-contacting biomaterials may enhance spontaneous re-endothelialization and/or hasten the confluence of transplanted endothelial cells.     

New prostheses for venous substitution

In 81 Beagle dogs, 6 cm long segments of the inferior vena cava were replaced end-to-end by artificial vascular grafts (10 mm in diameter) without an av-fistula and anticoagulant drugs. Different graft materials have been used, such as various e-PTFE (30-90 microns fiber length) and polyurethane with low and increased microporosity. e-PTFE with 75 microns fiber length and polyurethane with increased porosity showed the best tissue incorporation, complete endothelialization of the whole length and a high patency rate of 80-85% after a follow-up of 12 months. In contrast to other commercially available vascular grafts (textile woven or knitted, e-PTFE 30 microns) tested in previous series, polyurethane and e-PTFE with increased microporosity had already achieved complete endothelialization after 6-12 weeks. Therefore, these optimized prostheses should be introduced into clinical practice for large venous substitution. Thereafter, an adjunctive av-fistula as protection is probably no longer necessary.     

Endothelial cell transplantation

After more than 20 years of autologous endothelial cell transplantation, controversy is slowly giving way to consensus. The ongoing discussion regarding the optimal methods of creating an endothelial layer on synthetic vascular prostheses has been replaced by the realization that both in vitro endothelialization with cultured venous endothelial cells and mixed microvascular sodding result in equilibrated luminal tissue layers covered by a persistant endothelium. Clinical trials with almost 200 in vitro endothelialized prostheses are in their 10th year, and patency results are distinctly better than in nonendothelialized prostheses, particularly in below-the-knee grafts.     

Patency and healing of polymeric microvenous prostheses implanted into the rat femoral vein by means of the sleeve anastomotic technique

The sleeve anastomotic technique was used to enhance the longer term patency and healing of polyurethane-based (PU) microvenous prostheses (ID: 1 mm, length: 5 mm, wall thickness: 0.2 mm; n = 34) in the rat femoral vein. In the control group, PU prostheses (n = 12) were implanted by means of the conventional end-to-end technique, and all were found to be occluded after one day (n = 6) and three weeks (n = 6). In the other experimental groups, the prostheses were evaluated after one day (n = 6), three weeks (n = 10), and six weeks (n = 18) of implantation by means of routine light- and scanning-electron microscopy. The occluded prostheses in the control group demonstrated a firmly attached mural thrombus at the anastomoses at one day and a completely organized thrombus at three weeks after implantation. Thirty-one of the 34 PU prostheses implanted by means of the sleeve technique were patent. At one day, all patent PU prostheses (five out of six) demonstrated minimal thrombus accumulation and a smooth transition at the anastomotic sites. At three and six weeks, all patent PU prostheses (16 out of 18) were covered by a complete endothelial layer. Underneath the endothelial layer, a subendothelial layer, composed of two to four layers of smooth muscle cells, could be observed. The wall of the prostheses were penetrated by fibrohistiocytic tissue. Stenosis was not observed. These results demonstrate that the sleeve anastomotic technique not only improves the short-term patency of PU microvenous conduits, but also the longer-term patency rate.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Comparative Evaluation of two Types of Dacron Vascular Prostheses

The function of two types of Dacron vascular prostheses was evaluated in dogs using the abdominal aorta, inferior vena cava and iliac artery as host vessels. The transplants used were woven and knitted DeBakey prostheses and knitted Cooley prostheses. It is concluded that the function of a prosthesis with a diameter less than 5 mm is unsatisfactory. The same is true of a prosthesis implanted on the venous side, even in a large vein, such as the inferior caval vein, with a high flow. There is no significant difference between the function of DeBakey and Denton Cooley prostheses.     

Does porosity matter?

Patients who had survived at least four years after aortic aneurysmectomy were divided into two groups depending on the prosthesis being of woven or knitted fabric. Such prostheses do not develop an endothelial lining in man, and remain thrombogenic despite their great practical success. A comparison of the persistence versus the loss of palpable pulses distal to the prosthesis, was taken as an index of thrombogenicity and the formation of micro-emboli. There was a statistically significant difference in the persistence of distal pulses in patients with knitted grafts in the 5th, 6th and 7th years of the study, suggesting that such grafts are less prone to thromboembolic activity than the woven prostheses.     

Histopathological evaluation of woven and knitted Dacron grafts for right ventricular conduits: a comparative experimental study

Composite extracardiac conduits consisting of a low-porosity woven graft and a high-porosity knitted double-velour Dacron graft presealed with fibrin glue were implanted between the right ventricle and the pulmonary artery in 6 dogs under partial heparinization. Two grafts were explanted after 6 weeks, 2 after 12 weeks, and 2 after 6 months. The healing properties of both types of prosthesis were studied macroscopically, under light microscopy, and with scatter electron microscopy. Spontaneous peeling of both the inner and outer capsules of the graft occurred in 3 of 6 woven prostheses during transection. In the remaining 3, peeling could be easily induced by blunt dissection; this was impossible in the knitted grafts. Microscopically, in a comparison of the different weaves after identical time intervals, the inner capsule was noticeably thicker in woven than in knitted grafts. Transtitial ingrowth of fibroblastic tissue could be observed in knitted grafts after 6 weeks; only poor transmural tissue bridging was detectable in woven prostheses after 6 months. Neovascularization of the inner capsule was detectable earlier and was more advanced toward the luminal surface of highly porous grafts. In conclusion, knitted grafts in the position of extracardiac right ventricular conduits showed firmer attachment of both inner and outer capsules to the prosthetic material. Also, the inner capsule remained thinner and revealed a higher degree of neovascularization than in the woven Dacron grafts.     

Geometric comparison of aortic bifurcation prostheses to the normal and atherosclerotic human aorta, and clinical trial of a vertical seamed bifurcation prosthesis

The 12 bifurcation prostheses generally available in the United States were compared. One was woven Teflon, two woven Dacron, and nine knitted Dacron. Ten were "seamless" in construction, and two were "seamed," but close examination revealed that all prostheses actually were seamed at the bifurication point. The grafts varied considerably in construction, porosity, and geometry. To compare the geometries, each prosthesis was preclotted in plasma, inflated to 120 mm. Hg, and quick frozen in alcohol and dry ice. Transverse and frontal bisections of the frozen specimens were photographed with a millimeter scale for sizing. For comparison, eight human aortofemoral bifurcations were distended and frozen similarly. The prostheses had far wider bifurcation shelves than did the normal aortas. The five normal human aortofemoral bifurcations had an average ratio of limb: body diameter of 0.61; the three atherosclerotic specimens averaged 0.49. The prostheses had an average limb:body diameter ratio of 0.48. or the "seamless" grafts, 0.48 for the circular transverse limb-seamed grafts, and 0.58 for the vertical-seamed grafts. Vertical-seamed aortic bifurcation grafts implanted in 102 patients between 1970 and 1976 (average follow-up, 29.5 months) have developed only a single limb closure, at 53 months.     

Rapid endothelialization of vascular prostheses by seeding autologous venous tissue fragments.

A method was developed to obtain rapid endothelialization of a fabric vascular prosthesis by seeding autologous venous tissue fragments into its wall. In an animal study, complete endothelialization was observed in the entire inner surface of the prosthesis within 2 weeks after implantation. A piece of peripheral vein was minced with scissors and then stirred into saline to create a tissue suspension. This suspension was enmeshed into the wall of a highly porous fabric vascular prosthesis by repeated pressurized injections with a syringe. The prostheses (7 mm inside diameter and 5.7 cm in length), seeded with tissue fragments, were implanted into the descending thoracic aorta of 25 dogs, and they were removed from 1 hour to 2 months after implantation. Twenty-five prostheses, preclotted with fresh blood, were used as control prostheses. In the seeded graft, a thin fibrin layer covered the inner surface just after implantation, but countless numbers of endothelial cells migrated from the fragments and came up to the luminal surface like multiple "mushrooms" under the fibrin layer. Smooth muscle cells made multiple layers underneath the endothelial cell layer. The healing proceeded equally at every part. By this active migration and proliferation, the inner surface was completely healed within 2 weeks.     

Development and long-term fate of a cellular lining in fibrous polyurethane vascular prostheses implanted in the dog carotid and femoral artery. A scanning and light microscopical study up to 53 months after implantation.

The development and long-term fate of the inner cellular lining in 72 small caliber (3 mm inner diameter) fibrous polyurethane vascular prostheses explanted from dog carotid and/or femoral arteries at times ranging from 1.5 weeks up to 53 months after implantation were studied by scanning electron and light microscopy. A continuous cellular ingrowth from the vascular stumps into the 3 cm long prostheses was observed, which eventually resulted in a complete cellular lining 6 months after implantation. No other ways of endothelialization were noted. In fully endothelialized prostheses, the cellular ingrowth extended approximately 8 mm into the prostheses and consisted of several layers of fibroblasts and smooth muscle cells, covered by a very thin endothelioid cell layer. The newly developed lining was firmly anchored onto the inner prosthetic surface by means of cellular protrusions extended into the fibrous texture of the prosthetic wall. It was concluded that under experimental conditions in the dog complete endothelialization can be obtained in fibrous polyurethane vascular prostheses and that the lining remained thin and stable throughout the observation period of 53 months after implantation.     

Leiomyosarcoma of the urinary bladder in a patient with bilateral retinoblastoma

Abstract:   We report a case of bladder leiomyosarcoma in a 27-year-old woman who had previously been treated with surgery and radiation for bilateral retinoblastoma. The patient was admitted to hospital with discomfort on micturition. Cystoscopy revealed a bladder tumor covered by normal urothelium. Transurethral resection of the bladder tumor was performed, and the histopathological diagnosis was leiomyosarcoma. Partial cystectomy was performed. The leiomyosarcoma of the bladder did not invade the muscle layer. However, bladder tumors recurred at new intravesical locations repeatedly. After transurethral resection of the bladder tumor had been performed twice, total cystectomy and creation of an ileal conduit were performed.     

Development of an artificial vessel lined with human vascular cells

OBJECTIVES: Thrombogenity of small-diameter vascular prostheses might be reduced by complete coverage of the luminal surface with vascular cells. We investigated cell seeding on polyurethane vascular prostheses. METHODS: Thirty polyurethane vascular prostheses were divided into 3 groups of 10 each: group A, diameter of 20 mm and gamma-sterilized; group B, diameter of 4 mm and gamma-sterilized; and group C, diameter of 4 mm and ethylene oxide sterilized. Human smooth muscle cells, fibroblasts, and endothelial cells were isolated from saphenous vein segments and expanded in culture. Five polyurethane vascular prostheses of each group were seeded with endothelial cells alone (mean, 4.8 +/- 1.2 x 10(6) cells), and the remaining 5 polyurethane vascular prostheses were preseeded with a mixed culture of fibroblasts and smooth muscle cells (mean, 7.7 +/- 2.3 x 10(6) cells), followed by endothelial cell seeding (mean, 4.4 +/- 0.9 x 10(6) cells). Seven days after cell seeding, the polyurethane vascular prostheses were perfused under a pulsatile flow (80 pulses/min, 140/80 mm Hg, and 120 mL/min) for 2 hours. Specimens were taken after each seeding procedure both before and after perfusion and then examined both with a scanning electron microscope and immunohistochemically. RESULTS: Isolated endothelial cell seeding revealed better initial adhesion in groups A and B than in group C (63% vs 33%). After 7 days, the cells had covered approximately 80% of the luminal surface in groups A and B, whereas group C cells rounded up and lost adhesion. After perfusion testing of group A and B prostheses, only 10% of the surface was still covered with endothelial cells. Preseeding with the mixed culture again revealed a better initial adhesion in groups A and B compared with that in group C (76% vs 41%). In groups A and B endothelial cell seeding (adhesion, 72%) resulted in a confluent endothelial cell layer. The results of immunohistochemical staining were positive for collagen IV, laminin, CD31, and Factor VIII. In group C only isolated cells were found after each seeding procedure, which rounded up and vanished during the next days. Perfusion testing of group A and B prostheses revealed that the confluent cell layer remained stable, with only small defects (<10% of the surface). The cells stained positivively for endothelial nitric oxide synthase. CONCLUSION: Seeding of a mixed culture out of fibroblasts and smooth muscle cells resulted in improved endothelial cell adhesion and resistance to shear stress. This outcome was caused by an increased synthesis of extracellular matrix proteins. Cell attachment was better on gamma-sterilized polyurethane vascular prostheses compared with on those undergoing ethylene oxide sterilization.     

A collagen coated vascular prosthesis

A woven, double velour Dacron vascular graft was made nonporous by coating it with a layer of collagen prepared from fresh, young calf skin. Grafts were implanted in the thoracic aorta of 24 mongrel dogs and were examined at intervals up to 180 days. The grafts did not require preclotting or special preparation before being implanted. They sutured easily and did not bleed. When explanted all grafts were patent and covered with neointima. The bovine collagen was almost completely resorbed by 90 days and was replaced with native tissue. The collagen was neither thrombogenic, antigenic, cytotoxic, or pyrogenic.