Practical considerations in fabric vascular grafts. Introduction of a new bifurcated graft

A new bifurcation graft is introduced which conforms to the anatomic requirements of the aortoiliac segment. The graft material is made of 70 denier Dacron fiber manufactured in a warp-knit to prevent excessive fraying and to decrease porosity. Porosity studies indicate that the new material is approximately half as porous as other available Dacron graft materials. The new graft sizes of 12 by 7 and 14 by 8 mm more closely approximate the human aorta and common iliac arteries than do other available standard bifurcation grafts.The new bifurcation prosthesis has been used as an arterial bypass graft in 135 patients requiring surgery for aortoiliac occlusive disease. Of these patients, 64 per cent did not require blood replacement during surgery. The early operative results are comparable with those of other reported series.     

Experimental comparison of albumin-sealed and gelatin-sealed knitted Dacron conduits. Porosity control, handling, sealant resorption, and healing.

Two high-porosity knitted Dacron vascular grafts sealed with aldehyde cross-linked gelatin or albumin were compared with respect to the following characteristics. Porosity control by the absorbable sealant was assessed with a water porosity meter at 120 mm Hg pressure. Ease of suturing was determined by an objective needle penetration test. Sealant resorption was assessed histologically in a subcutaneous immature rat model as well as in circulatory implants. Gross and microscopic healing characteristics were compared in circulatory implants in the thoracic aorta of sheep with use of a composite conduit in every animal, which allowed direct comparison of the two graft materials and minimized differences in healing between individual animals. Both grafts demonstrated excellent porosity control and better handling characteristics than woven Dacron. Sealant resorption was generally rapid, although residual albumin sealant was often seen adjacent to anastomoses. Residual sealant appeared to result in focally poor healing with focal loss of adhesion of surrounding tissue to graft. We conclude that details of sealant preparation and application can importantly influence the performance of presealed knitted Dacron grafts and should be carefully evaluated in the laboratory before clinical implantation is begun.     

Ingrowth of aorta wall into stent grafts impregnated with basic fibroblast growth factor: a porcine in vivo study of blood vessel prosthesis healing

OBJECTIVE: Endovascular aneurysm repair is an alternative treatment of abdominal aortic aneurysm. The procedure is less invasive, and morbidity and most probably mortality are reduced. However, some problems, such as endoleakage, are yet to be resolved. Endoleakage can occur after graft migration, as a result of insufficient fixation of the stent graft. One cause is deficient healing between the aortic neck and the stent graft. We hypothesize that better healing, achieved by induction of vascular cell ingrowth into the graft material, results in better graft fixation. Previously we demonstrated ingrowth of neointima into the graft material if the stent graft is impregnated with a coat of basic fibroblast growth factor (bFGF), heparin, and collagen. In this study we evaluated healing with bFGF-heparin-collagen-coated stent grafts in vivo. METHODS: In 4 pigs, 32 endovascular stent grafts, manufactured from standard Dacron and Gianturco Z-stents, were placed in the aorta. The stent grafts were impregnated with either bFGF-heparin containing collagen (n=16) or control collagen (n=16). After 4 and 8 weeks animals were killed, and ingrowth and healing of the stent grafts were macroscopically and electron microscopically evaluated. RESULTS: After 8 weeks all bFGF-impregnated stent grafts demonstrated ingrowth of tissue and healing between the graft and the aorta, whereas the control nonimpregnated stent grafts showed no ingrowth. Microscopic evaluation demonstrated alpha-smooth muscle actin-positive cells, most probably smooth muscle cells or myofibroblasts, growing from the vascular wall through the graft material. CONCLUSION: A Dacron prosthesis impregnated with collagen, heparin, and bFGF induced graft healing in an in vivo pig model, in contrast to nonimpregnated stent grafts. This in vivo study confirms our previous findings in vitro. These results indicate that healing between Dacron and the aorta can be achieved, and suggest that type I endoleakage may be resolved by inducing healing between the aortic wall and the prosthesis with graft material containing growth factor.     

Modified vein allograft for small arterial reconstruction in dogs

The ideal graft for peripheral arterial reconstruction has yet to be developed. We evaluated on the effectiveness of porosity to intimization of the graft. Modified vein allografts newly constructed through digestion of vein allografts with elastase, glutaraldehyde tanning and lyophilization were implanted in thirty-nine canine femoral arteries. These grafts had a higher porosity than conventional vein allografts and the overall patency rate was 70 per cent at 6 months after implantation. Microscopic examination showed that graft interstitial healing and subsequent intimization were completed by ingrowth of connective tissue from outside through the graft wall at 3 weeks and later. Aneurysmal change of the modified vein allografts was never evident. These results indicated that porosity of the graft is indeed an important factor for intimization and durability of grafts, even in bioderivative substitutes.     

Modified vein allograft for small arterial reconstruction in dogs

The ideal graft for peripheral arterial reconstruction has yet to be developed. We evaluated on the effectiveness of porosity to intimization of the graft. Modified vein allografts newly constructed through digestion of vein allografts with elastase, glutaraldehyde tanning and lyophilization were implanted in thirty-nine canine femoral arteries. These grafts had a higher porosity than conventional vein allografts and the overall patency rate was 70 per cent at 6 months after implantation. Microscopic examination showed that graft interstitial healing and subsequent intimization were completed by ingrowth of connective tissue from outside through the graft wall at 3 weeks and later. Aneurysmal change of the modified vein allografts was never evident. These results indicated that porosity of the graft is indeed an important factor for intimization and durability of grafts, even in bioderivative substitutes.     

The effect of pancreatopeptidase E (elastase) on anastomotic intimal thickness in two types of vascular prosthesis

To determine the effects of pancreatopeptidase E (elastase) on anastomotic intimal thickness in vascular prostheses, expanded polytetrafluoroethylene (ePTFE) and Dacron grafts were implanted in the infrarenal aortas of 28 adult mongrel dogs, divided into four groups of seven dogs each according to the type of graft used and whether or not elastase was given. Thus, group E received ePTFE grafts without elastase; group D received Dacron grafts without elastase; group E + Ela received ePTFE grafts with concomitant oral elastase, 8 mg/kg per day; and group D + Ela received Dacron grafts with elastase given at the same dosage as in group E + Ela. Each graft was harvested 4 months following surgery for histologic examination. It was clearly observed that elastase suppressed intimal growth at the proximal and distal anastomoses in the ePTFE grafts (P<0.05), but not in the Dacron grafts. Furthermore, when we measured the smooth muscle cell percent extinction (%E) on microspectrophotometry in the intima within 2 mm of the proximal and distal anastomoses, it was found that elastase reduced intimal smooth muscle proliferation at the anastomosis of the ePTFE grafts, but not the Dacron grafts (P<0.05). These data suggest that elastase suppresses intimal growth by inhibiting smooth muscle cell migration and proliferation in the vascular prostheses of low but not of high porosity.     

Compliance properties of conduits used in vascular reconstruction

BACKGROUND: Compliance mismatch between native artery and prosthetic graft used for infrainguinal bypass is implicated in the aetiology of graft failure. The aim was to quantify the elastic properties of a new compliant poly(carbonate)polyurethane (CPU) vascular graft, and to compare the compliance properties of grafts made from CPU, expanded polytetrafluoroethylene (ePTFE), Dacron and human saphenous vein with that of human muscular artery. METHODS: A pulsatile flow phantom was used to perfuse vessel and prosthetic graft segments at physiological pulse pressure and flow. Intraluminal pressure was measured using a Millar Mikro-tip catheter transducer and vessel wall motion was determined with duplex ultrasonography using an echo-locked wall-tracking system. Diametrical compliance and a stiffness index were then calculated for each type of conduit over mean pressures ranging from 30 to 100 mmHg by 10-mmHg increments. RESULTS: The compliance values of CPU and artery (mean over the pressure range) were similar (mean(s.d.) 8.1(0.4) and 8.0(5.9) per cent per mmHg x 10(-2) respectively), although the elastic behaviour of artery was anisotropic unlike CPU, which was isotropic. Dacron and ePTFE grafts had lower compliance values (1.8(1.2) and 1.2(0.3)per cent per mmHg x 10(-2) respectively, averaged over the pressure range). In both these cases, compliance and stiffness differed significantly from that of artery over a mean pressure range of 30-90 mmHg. Human saphenous vein exhibited anisotropic behaviour and, although compliant at low pressure (30 mmHg), was markedly incompliant at higher pressures. CONCLUSION: Compliant polyurethane grafts offer a greater degree of compliance match than either ePTFE or Dacron.     

Interposition grafting for portal hypertension

During the past six years, thirty-seven patients underwent interposition graft shunting for thirty-three instances of bleeding from varices and five instances of intractable ascites, either electively (twenty-seven instances) or as an emergency (eleven instances). Autogenous jugular vein was used in twenty-five instances, homologous vena cava in nine, and Dacron in four. Portacaval and mesocaval anastomoses were done in equal numbers (nineteen). Using Childs' method of clinical evaluation, thirty-three patients were Class C and four Class B. There were five (13.2 per cent) early deaths with one (3.5 per cent) in the elective and four (36 per cent) in the emergency group. Twelve grafts were open at autopsy, fifteen at splenoportography, and seven assumed patent because patients were asymptomatic. Two Dacron grafts and two homografts thrombosed. There were ten late deaths, only one related to graft failure. Apparently, the operation controls ascites, with autogenous jugular vein being the ideal material. Interposition grafting is a simple, safe procedure that can be used for portal decompression in patients with bleeding varices.     

Effects of fibronectin bonding on healing of high porosity expanded polytetrafluoroethylene grafts in pigs

BACKGROUND: We developed a new fibronectin bonding to expanded polytetrafluoroethylene (ePTFE) and previously reported that, in a dog carotid implant model, fibronectin bonding improves graft healing in high porosity ePTFE grafts. The purpose of this study was to further investigate the effect of the fibronectin bonding on graft healing in a pig carotid implant model. METHODS: Fifteen pigs received a high porosity ePTFE graft treated with the fibronectin bonding (fibronectin-bonded graft) on one side and an untreated graft (non-bonded graft) on the contralateral side. The grafts were explanted at intervals of 3 and 6 weeks and subjected to histological studies. RESULTS: At 3 weeks, the neointima of fibronectin-bonded grafts was better organized than that of non-bonded grafts. At 6 weeks, the morphologic features of the neointima were the same in fibronectin-bonded and non-bonded grafts. The neointima was completely organized. CONCLUSIONS: Together with the previous results with the dog model, fibronectin bonding could be expected to improve healing of the high porosity ePTFE grafts in humans.     

Femoropopliteal bypass in elderly diabetic patients.

The records of sixty-nine consecutive elderly diabetic patients over age 70 years who underwent femoropopliteal bypass at the New England Deaconess Hospital from 1966 to 1975 were reviewed and analyzed statistically. Grafts were classified as patent only if the patient had a palpable distal pulse postoperatively. No hospital deaths occurred. The patency rate declined with decreasing runoff below the knee. Patients receiving insulin had a patency rate of 7 per cent, compared with a rate of 35 per cent in patients treated with diet or oral agents (p < 0.05). Cross analysis disclosed no other significant difference between these two groups. No benefit from Dextran was demonstrable in our series. Graft closure carried a 36 per cent risk of above knee amputation. Life table analysis of patients who underwent autogenous vein graft (fifty-seven patients) showed one and three year patency rates of 72 and 56 per cent, respectively. Conversely, grafts of Dacron had one and three year patency rates of 48 per cent and less than 10 per cent, respectively. In a favorable subset of twenty-six patients who (1) were receiving insulin, (2) had either previously successful bypass or no previous vascular surgery, (3) had arteriographic evidence of one or more vessel runoff, and (4) had autogenous vein grafts, the one and three year patency rates were 91 and 82 per cent, respectively. Our experience shows that femoropopliteal bypass is safe and effective when patients are carefully selected. We strongly discourage the use of Dacron materials in elderly diabetic patients.     

Heat-denatured albumin-coated Dacron vascular grafts: physical characteristics and in vivo performance

Dacron fabrics with a wide range of porosities were autoclaved for 3 minutes after being soaked in serum, 5% albumin, or 25% albumin. Porosity of compound Dacron grafts made with 25% albumin was less than 1 ml/min/cm2 regardless of the fabric base, whereas porosity of grafts made with serum or 5% albumin was proportional to the porosity of the base fabric. Porosity of the compound grafts remained stable for more than 48 hours and to pressure greater than 450 mm Hg, if the grafts were kept moist. Tubes of Marlex mesh coated with heat-denatured albumin, implanted as infrarenal aortic replacements in dogs, showed complete albumin absorption by 3 weeks. However, perigraft tissue reaction and graft incorporation were minimal and extensive false aneurysm formation resulted. Knitted filamentous Dacron 6 mm tubes coated with heat-denatured albumin were implanted as iliofemoral bypass grafts in 12 dogs, with blood-preclotted knitted filamentous Dacron grafts implanted as contralateral control grafts. Comparison of the albumin-coated grafts with the blood-preclotted control grafts showed no differences in healing or patency at 4 to 6 months. Heat-denatured 25% albumin forms a strong and hemostatic coating regardless of fabric base. Albumin-Dacron compound grafts are easily and rapidly made in the operating room, handle well, and are suitable for large and medium-sized arterial replacements without changes in healing or patency. Because of slow tissue incorporation, however, albumin-coated knitted Dacron grafts should be avoided in patients who require long-term anticoagulation therapy.     

Effects of autologous mesothelial cell seeding on prostacyclin production within Dacron arterial prostheses

Canine abdominal aortas have been replaced with Dacron arterial prostheses to assess the effects of mesothelial cell seeding on graft prostacyclin and thromboxane A2 release. At both 2 weeks and 6 weeks after surgery, three seeded and two unseeded control grafts were examined for prostacyclin release. In addition, thromboxane release was assessed in one seeded and one unseeded graft. Sections of aorta and graft were removed and incubated in PBS containing either 10 microM calcium ionophore A23187 or 20 microM arachidonic acid. The incubation mixture was sub-sampled at 5 min intervals over a 20 min period to assess the progressive release of prostacyclin and thromboxane A2 using a radioimmunoassay for 6-keto-prostaglandin F1 alpha and thromboxane B2 respectively. In seeded grafts, 6-keto-prostaglandin F1 alpha release averaged 15 per cent compared with aorta at 2 weeks and 45 per cent compared with aorta at 6 weeks. By contrast, release from unseeded grafts was undetectable at 2 weeks; however, by 6 weeks there was some release amounting to 15 per cent compared with aorta. There was a statistically significant increase in the release of 6-keto-prostaglandin F1 alpha from mesothelial cell seeded grafts at 6 weeks compared with unseeded grafts (P less than 0.01). Thromboxane release from the graft sections was variable and unrelated to whether the grafts had been seeded or not. These preliminary results, showing that grafts seeded with autologous peritoneal mesothelial cells release more prostacyclin than unseeded grafts, further highlight the role of the mesothelial cell as an alternative to the endothelial cell for improving the patency of arterial Dacron prostheses in the early postoperative days.     

Experimental evaluation of ten clinically used arterial prostheses

The arterial grafts currently in use are classified into five basic categories; 10 different commercially available prostheses were chosen to represent these categories. The Vascutek and Bionit are made from knitted Dacron and have medium porosity, requiring preclotting by the surgeon. The DeBakey Soft Woven and Plasma TFE grafts are made from woven Dacron and have low porosity, not requiring preclotting under most circumstances. Also studied were woven and knitted grafts with leakage resistance referred to as impervious Dacron grafts: the Vascutek Gelseal, the Bard Albumin Coated DeBakey Vasculour II, the Microvel with Hemashield, and the albumin saturated, autoclaved DeBakey Soft Woven graft. Gore-Tex and Impra are expanded polytetrafluoroethylene grafts which do not require preclotting. For each type, five grafts 6 cm long and 8 mm in diameter were implanted in the descending thoracic aorta of healthy adult dogs for 16 weeks. The physical characteristics, biocompatibility, and healing patterns varied according to the structure and treatment of the grafts. Pretreatment with biomaterials during manufacture is quite effective in preventing transinterstices blood loss during implantation, but results in altered physical qualities, increased thrombogenicity and delayed healing in comparison to the effects of preclotting with autogenous blood at the time of implantation.     

Tetrazolium reductase as an index of viability of stored skin

The take or failure of 264 split-skin grafts on burned patients has been investigated; the single most important reason for failure was non-viability of the graft at its time of application, as measured by the relative tetrazolium reductase (TR) activity. There was a high correlation between relative TR activity of less than 50 per cent and graft failure, and between TR activity of greater than 50 per cent graft take.The longest period for which a graft could be stored at ?10°C and remain viable was 12 days; a few were non-viable before 10 days. Repeated freezing and thawing of stored skin grafts reduced the length of viability by 40 per cent compared with grafts which had been frozen and thawed only once.The tetrazolium reductase activity provides a quick reliable prognostic indication of whether or not a graft should be applied with the anticipation of a take.     

Mechanisms of healing in synthetic grafts

In previous baboon studies we have shown that porous (60 micron mean internodal distance) polytetrafluoroethylene (PTFE) grafts heal by ingrowth of endothelium and smooth muscle cells from the adjacent artery and from capillaries penetrating through the interstices of the graft. However, porous grafts (principally made of Dacron) in humans do not heal. This has been attributed to a wound healing deficiency in humans; however, it might be due to an inhibitory effect of the Dacron itself. To examine the latter possibility, we undertook this study to compare the healing of 4 mm internal diameter porous Dacron grafts (USCI, Sauvage Filamentous Knitted) with that of Gore-Tex 60 micron PTFE grafts in baboons (the latter graft not available for clinical use). The grafts were harvested at 2, 4, and 12 weeks and assessed for (1) percentage of endothelial coverage, (2) endothelial cell (EC) proliferation (thymidine labeling index), (3) intimal area, and (4) smooth muscle cell (SMC) proliferation (thymidine labeling index). The PTFE grafts at all three time points were fully covered, whereas only one of five Dacron grafts was completely covered at 12 weeks. The intima of the PTFE grafts consisted of ECs and SMCs, whereas that of the Dacron grafts contained ECs and SMCs as well as focal accumulations of thrombus. The intimal cross-sectional areas in the Dacron grafts (3.0 +/- 1.2 mm2) were significantly greater than in the PTFE grafts (0.8 +/- 0.6 mm2) at 4 weeks; there was no difference at 12 weeks (Dacron, 2.6 +/- 2.3 mm2 and PTFE, 3.0 +/- 2.5 mm2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Capillary and venule proliferation in the healing process of Dacron venous grafts in rats.

A woven, noncrimped graft (made of Dacron and coated with an elastomer) that was 1.5 mm in diameter and 15 mm long was capable of replacing the vena cava in rats. The elastomer mixture consisting mainly of silicone rubber was necessary to bond the woven Dacron fibrils of the woven graft to prevent fraying at the anastomoses and bleeding through the interstices of the lightly woven, fairly high porosity (500) conduit. Sequential histologic studies showed that patency was associated with the ingrowth of small venules and the spreading of endothelial cells from each anastomosis toward the center. Small venules appeared in loose connective tissue, forming a pseudointima 12 days after grafting. This process occurred in the midportion of the graft before pannus endothelial growth covered the endothelial surface. Various thicknesses of the external polymer coat were studied for their influence on healing. None of the grafts developed a thrombus in these latter studies, and regardless of the thickness of the external elastomer, endothelial resurfacing was complete at 30 days. However, the graft with the thinnest external elastomer coating had the best-formed vasa vasorum, and the intima at both the anastomoses and midportions of the graft was significantly thinner than intima found in grafts of other composition. We conclude that this woven Dacron polygraft provides a surface resistant to early thrombosis; that healing occurs mainly by pannus ingrowth, but external and interstitial factors are also important; and that properties inherent in the polygraft wall determine the size of the residual lumen.     

Aorto-iliac reconstructions for intermittent claudication

Over a 12-year period, 290 aortofemoral reconstructions were performed for intermittent claudication involving 449 legs in 262 patients. The accumulative patency rate in surviving patients was 79 per cent at 5 years. The patency rate was significantly better in patients who stopped smoking after operation, and in men compared with women. Dacron grafts were significantly more successful than endarterectomy in men. If there was no associated superficial femoral artery occlusion, endarterectomy and Dacron bypass grafts were equally successful, but Dacron bypass grafts were significantly superior to endarterectomy if the superficial femoral artery was severely stenosed or occluded. The success rates for improving the patients' intermittent claudication were 90 per cent at 3 months and 72 per cent at 3 years. The success rate at 3 years was 80 per cent if the superficial femoral artery was patent but only 62 per cent if the superficial femoral artery was severely stenosed or occluded. Mortality and morbidity rates fell markedly in the last 6 years of the study.     

An in vitro study of the properties influencing Staphylococcus epidermidis adhesion to prosthetic vascular graft materials.

This study examines the influence of the properties of various vascular graft materials on the bacterial adherence process of two different strains of Staphylococcus epidermidis (mucous and normucous producing). Dacron grafts (both knitted and woven), Teflon grafts, and Dacron grafts coated with one and two layers of silicone were studied because these materials differ significantly in porosity, hydrophobicity, and surface charge (zeta potential). Graft segments were immersed in 3H-labeled bacteria solution for periods ranging from 5 to 180 minutes and liquid scintillation techniques were used to quantify bacterial adherence. The porous knitted Dacron material had a significantly higher rate of bacterial adherence than either the woven Dacron or Teflon (p less than 0.05). Silicone coating (either one or two layers) reduced adherence by a factor of four for the knitted Dacron (p less than 0.05) and by a factor of two for woven Dacron (p less than 0.05). The mucous producing strain of S. epidermidis displayed significantly better adherence to woven and knitted Dacron than the normucous producing strain, but only when 0.25% dextrose was added to the bacteria solution. These findings indicate that the highly porous knitted Dacron grafts have the highest propensity for bacterial adhesion. Graft materials with the most negative zeta potentials are more resistant to bacterial adherence. Silicone coating of Dacron material significantly changed adherence characteristics, suggesting that this may be a viable strategy for protecting implantable medical devices containing materials to which bacteria readily adhere.     

How should we preclot knitted Dacron grafts?

We studied the change in water porosity over time of 10 Sauvage Bionit-II and 10 DeBakey Vasculour-II knitted velour Dacron grafts throughout the four stages of the Sauvage preclotting technique. Graft porosity decreased significantly (p less than 0.001) at the ends of stages 1 and 2 for both types of grafts, but stages 3 and 4 did not further reduce graft porosity. These results demonstrate that a two-stage preclotting technique is adequate for the preclotting of knitted velour Dacron grafts. A final rinse with heparinized blood is recommended as this may reduce graft thrombogenicity.     

Long-term evaluation of a new selectively biodegradable vascular graft coated with polyethylene oxide-polylactic acid for right ventricular conduit. An experimental study

Low-porosity woven Dacron grafts have been used extensively as an extracardiac conduit in the surgical treatment of congenital and acquired heart diseases involving total heparinization. Caution is still warranted in their use, however, because of long-term complications, including calcification and development of obstructive fibrous peel. In contrast, high-porosity grafts offer much better tissue anchorage and healing but cannot be used under heparinization. We have developed a compound vascular prosthesis in which a knitted Dacron graft is coated with a polymeric biodegradable sealant. Polyethylene oxide-polylactic acid-segmented copolymers comprised the degradable component of the graft. In vitro studies showed that the coated prosthesis exhibited a highly flexible elastomer-like mechanical response. The prostheses were completely watertight, and significant degradation started after 1 week, with absorption completed after 3 weeks. Seven woven and six knitted polyethylene oxide-polylactic acid-coated Dacron grafts used as extracordiac conduits (16 mm), connecting the right ventricle and the pulmonary artery were implanted in dogs. The dogs were killed after 12 to 18 months, and the results are reported. Scanning electron microscopy examination showed peel detachment and nonhomogenous intimal surface with fenestrations in the woven graft group, but complete healing and incorporation of the pseudointima with homogenous, thin lining of the luminal surface in the polyethylene oxide-polylactic acid-coated group. Histologic studies indicated much superior healing and anchorage of the periprosthetic tissue and the pseudointima in the polyethylene oxide-polylactic acid-coated grafts. The biodegradable polymer was fully degraded and exhibited a complete incorporation of the compound vascular prosthesis. This study indicates the superior healing properties of these selectively biodegradable grafts, which might increase long-term patency and decrease complications of right ventricular conduits.