Primary anastomotic bonding in polytetrafluoroethylene grafts?

Previous studies have demonstrated that standard knitted and woven fabric grafts are forever dependent on the suture material for anastomotic tensile strength. Clinical experience with polytetrafluoroethylene (PTFE) and double velour knitted grafts have shown that there is extensive fibrous capsular bonding between the graft and the surrounding tissues. This would lead to increased anastomotic tensile strength. To test this theory, 34 mongrel dogs underwent replacement of their infrarenal aortas with grafts made of PTFE (10 dogs), of double velour knitted Dacron (DVD, 11 dogs), of single velour knitted Dacron (SVD, 5 dogs), and of woven Dacron (WD, 8 dogs). One anastomosis was constructed with 5-0 Prolene and the opposite anastomosis was constructed with 5-0 Dexon (average absorption time, 21 days). In five grafts each of PTFE and DVD, as well as in all eight WD grafts, the midgraft was divided and resutured with 5-0 Dexon. All grafts were harvested together with adjacent proximal and distal aorta between 3 and 10 months from the time of implantation. The tensile strength of each anastomosis was measured with a tensiometer. The mean graft-to-artery (absorbable suture) anastomotic tensile strength, in pounds, for PTFE (14.3) and DVD (12.6) was significantly higher than that for SVD (6.9) or WD (7.2) (p less than 0.003). Graft-to-graft anastomotic tensile strength for PTFE (mean 17.3) was significantly better than that for DVD (mean 9.0; p less than 0.03) or WD (mean 7.9; p less than 0.001). Analysis of anastomotic tensile strength as a function of time revealed continued increase in PTFE in contrast to a slow decline with time in DVD.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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

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

Aneurysm in a double velour knitted Dacron graft

Double velour knitted Dacron grafts are currently used for aorto-iliac arterial reconstructions to increase encapsulation and enable rapid intimization of the grafts. Reports of an aneurysm arising in the body of a double velour knitted Dacron graft are rare. We experienced a case of aneurysm arising in the body of an innominate-abdominal aortic bypass graft four years after implantation. Microscopically, this focal aneurysm seemed to be related to a structural defect in the manufacturing process. We wish to stress that patients with implanted commercial Dacron prostheses should be carefully and regularly followed.     

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.     

Bacterial adherence to vascular prostheses: A determinant of graft infectivity

An in vitro model was developed to quantitatively measure bacterial adherence to the surface of prosthetic vascular graft material. Four strains of bacteria (Staphylococcus aureus, nonmucin-producing S. epidermidis [SP-2], mucin-producing S. epidermidis [RP-12], and Escherichia coli) were used to inoculate expanded polytetrafluoroethylene (ePTFE), woven Dacron, and velour knitted Dacron graft material. After graft specimens were incubated in a 10⁷ suspension of bacteria, they were washed to remove nonadherent organisms and ultrasonically oscillated to dislodge adherent organisms. Quantitative culture of the sonication effluent was used to calculate bacterial adherence, expressed as the number of colony-forming units found in each square centimeter of graft material per 10⁷ inoculum. All bacterial strains had a greater affinity to velour knitted Dacron graft than to ePTFE (p < 0.025). E. coli and S. aureus adhered to velour knitted Dacron in greater numbers than to woven Dacron (p < 0.04). The production of extracellular polysaccharide (mucin) by the RP-12 strain significantly increased adherence to both ePTFE and Dacron grafts compared with the other three bacterial strains tested (p < 0.04). Although E. coli was less adherent to ePTFE than nonmucin-producing staphylococcal strains (S. aureus and SP-2), no difference in adherence to knitted or woven Dacron graft material was demonstrated. The differential adherence of bacteria to prosthetic vascular grafts pays an important role in the pathogenesis of graft sepsis and determines relative graft infectivity. The in vitro model developed is well suited for further study of the mechanisms by which bacteria adhere to and colonize vascular grafts. (J VASC SURG 1986;3:732-40.)     

Comparative surface thrombogenicity of implanted vascular grafts.

In order to study the comparative thrombogenicity of neointimal surfaces that develop with three types of vascular graft materials (ultralightweight knitted dacron, knitted dacron external velour, and expanded Teflon), 36 female mongrel dogs had their infrarenal aortas alternately replaced with one of the three grafts. At the end of 3 or 6 months, the grafts were removed and the surface thrombogenicity of the neointimal surface was determined. Each graft was examined visually and microscopically for evidence of “healing.” At 6 months the external velour graft is lined more frequently than the other two grafts. The external velour graft has a markedly better incidence of cellular healing noted microscopically than the other two grafts at both time intervals. While the expanded Teflon has an initially lower surface thrombogenicity (probably due to the characteristics of Teflon surface), at 6 months, the velour graft has the lowest surface thrombogenicity. This is most likely due to cellular healing. Of all the completely lined grafts at both time intervals, the surface thrombogenicity of the velour grafts was most like that of the normal aorta. The velour graft appears to develop the least thrombogenic neointimal surface while becoming most frequently healed with a cellular neointimal surface.     

Failure of dacron arterial prostheses caused by structural defects

We have observed unusual aneurysmal complications associated with structural defects of Dacron fabrics in three patients. The first patient had beadshape aneurysms along the course of the bilateral axillo-femoral prosthetic bypasses 4 or 5 years after surgery. Round defects or longitudinal rents in the lower third of the prostheses (Vascular-D knitted Dacron graft of high porosity, USCI) were the source of the aneurysmal complications. In the second patient, the transverse diameter of the aorto-femoral Dacron graft (Vascular-D, USCI) was increased to twice that of the original graft with formation of an anastomotic false aneurysm in the groin 3 1/2 years after surgery. The defective prostheses in these two cases were successfully replaced by Cooley double velour knitted Dacron grafts. The third patient developed an arterio-ureteral fistula originating from a round defect of the aorto-femoral prosthesis (Tetoron that is woven Dacron graft with a low porosity, Nakao-Filter, Japan) 8 years postoperatively and died from massive hematuria and subsequent disseminated intravascular coagulopathy. Microscopic examination of the removed prostheses revealed a complete loss of the conformation of the weave with fragmentation and disruption of the graft fibers. Therefore, patients with Dacron arterial prostheses should be followed up regularly and with great care.     

Implantation of homologous and heterologous aortic valves in prosthetic vascular tubes : An experimental study

Freeze-dried dog and pig aortic valves sutured within tubes of woven Teflon and knitted Dacron have been inserted into the descending aorta of 56 dogs with aortic incompetence. All the valves placed inside woven Teflon were destroyed, with one exception, where six months after insertion the valve was competent and in good condition. Most of the valves in knitted Dacron remained in good condition for up to three months after surgery. The few bad results with knitted Dacron were related to infection or bad haemodynamic conditions. There was no observable difference in behaviour between the homologous and the heterologous valves during the short follow-up of these experiments.     

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.     

Indium 111-labeled platelet deposition in woven and knitted Dacron bifurcated aortic grafts with the same patient as a clinical model

A study was designed to compare platelet deposition between knitted and woven Dacron grafts in the same patient. Twenty patients received aortoiliac or aortofemoral bifurcated Dacron grafts, each composed of one woven and one double-velour knitted limb. External nuclear graft imaging was carried out after injection of autologous platelets labeled with indium 111. The patients were studied postoperatively in time periods ranging from 6 days to 42 months. Platelet accumulation was almost identical in knitted and woven limbs in all patients. This study appears to indicate that there is no difference in thrombogenicity between knitted and woven bifurcated Dacron grafts in the aortoiliac or aortofemoral positions measured by platelet accumulation.     

Late rupture of knitted Dacron double velour arterial prostheses. Report on four cases

Late fibre breakage with longitudinal tears occurred in 4 patients of a series of some 300 implanted knitted Dacron double velour arterial prostheses. The four patients all received their grafts for occlusive aortoiliac disease in the year 1978, and the rupture was found 4 to 6 years later. Three of the failures occurred in axillo-bifemoral bypass grafts, whereas the fourth patient had a bifurcated aortic prosthesis. Dilatation was significant in the latter graft only. Structural weakness might appear during production, during later handling, or possibly as a result of interference from infected material or host factors. The cause of graft failures in the present series could not be ascertained. Whatever type of knitted Dacron used, a 2-3% incidence of graft deterioration might be expected. Therefore regular, life-long follow-up of patients with Dacron arterial prostheses seems warranted.     

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.     

Reinforced graft-to-artery anastomosis: an experimental study

This experiment was designed to study the effects of reinforcing graft-to-artery anastomoses. A section of infrarenal aorta was replaced with a Dacron graft in 24 dogs. In eighteen animals one anastomosis was reinforced with a cuff of Dacron graft material, while the remaining six dogs both anastomoses were reinforced, one with graft material and the other with Dacron mesh. The animals were sacrificed at three week to six month intervals. The grafts were examined grossly and microscopically, and the tensile strength of the anastomosis determined. There was no difference in tensile strength or in the luminal healing. There was only limited fibrous healing under the graft material cuff whereas there was full incorporation of the mesh cuff. Conclusions: Reinforcement is not required routinely. When used, the cuff should be made with mesh rather than graft material.     

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.     

Experimental study of tensile strength at arterioprosthetic anastomosis

An experimental study was conducted to investigate the possible role of the suture materials in occurrence of false aneurysms at the suture line. Mature mongrel dogs were used in the experiment. A segment of abdominal aorta was replaced by woven Teflon graft. Braided silk was used as the suture material on one side, and polyglycolic acid suture on the other. The dogs were sacrificed one to 16 weeks after the operation, and the implanted prostheses were excised along with the abdominal aorta. The tensile strengths of the anastomosis on both ends of the graft were calculated. The tensile strength of the braided silk consisted about 8% of the total tensile strength at 16 weeks after surgery. The degree of sliding of the synthetic graft at the anastomotic site and the outer layer of the graft were analyzed at each measurement of tensile strength. In the 1st Department of Surgery, Yokohama City University Hospital 125 arterial synthetic prostheses have been implanted in patients during 1964 to 1982. False aneurysms occurred in 9 cases. The incidence was 19.2% in the cases where silk suture material was used but was 4.0% when synthetic suture material was used. It was concluded that the use of synthetic grafts was preferable, since it conjoined well with the outer layer. Furthermore, the plastic suture material did not degenerate and seemed to prevent the occurrence of false aneurysm.     

A quantitative and qualitative comparison of fibrin glue, albumin, and blood as agents to pretreat porous vascular grafts

Recent reports suggest that fibrin glue can be used to seal porous vascular grafts prior to insertion, but this ability has not been quantitatively compared to existing methods. We compared blood loss from and handling characteristics of grafts pretreated with either fibrin glue (FG) (Tisseel), albumin autoclaving (AA), or blood preclotting (BP). Five 6-cm segments of 6-mm internal diameter grafts, both knitted and woven double velour Dacron were treated in each group (30 specimens). Human blood was forced through the BP group until clotted; AA segments were soaked in 25% human albumin and autoclaved for 10 min; FG segments were treated with a topical application of Tisseel (0.5 ml/graft) followed by treatment with topical thrombin + CACl (0.5 ml/graft). Graft ends were sealed and attached to a transducer/syringe pump mechanism which pumped heparinized human blood into the graft at 100 mm Hg intraluminal pressure. All blood that leaked through the grafts over 2 min was collected and the amount was averaged for the five grafts in each group. Graft handling was characterized as either pliable or stiff. Blood pretreatment caused 21 +/- 2 and 13 +/- 4 cc/2 min of leak in knitted and woven grafts, respectively. Albumin autoclaving resulted in 9 +/- 2 and 1 +/- 0.5 cc of leak (P less than 0.01 compared to blood), while fibrin glue produced 2 +/- 2 and 0.4 +/- 0.5 cc leaks (P less than 0.01 compared to blood). Both blood and fibrin glue produced soft pliable grafts, while albumin pretreatment resulted in stiff grafts.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of inner wall filamentousness on the performance of small- and large-caliber arterial grafts

Dacron prostheses with differing degrees of inner wall filamentousness were implanted in the canine descending thoracic aorta for 56 days (n = 14) and the carotid arteries for 21 days (n = 40). In the thoracic aorta the healed inner capsule of 8 mm internal velour grafts was approximately three times as thick as the inner capsule of external velour knitted prostheses. However, the early patency and rapidity of healing of these two types of prostheses were essentially the same. In the carotid arteries the patency of the 4 mm external velour prostheses was greater than that of the internal velour prostheses and the mean thrombus-free surface area of the external velour grafts was significantly greater than that of the internal velour grafts. These observations suggest that an internal velour surface is not deleterious to early patency in a large-caliber, high-flow artery but that it may be in a small-caliber, low-flow artery.     

Platelet Consumption by Arterial Prostheses: The Effects of Endothelialization and Pharmacologic Inhibition of Platelet Function

The thrombogenic mechanism of arterial grafts has been studied by determining the relative utilization of platelets, fibrinogen and plasminogen by human arterial prostheses, and by direct examination of arterial grafts in a baboon model. Forty-one survival and turnover measurements of (51)Crplatelets, (131)I-fibrinogen and (125)I-plasminogen in ten patients with aortofemoral knitted Dacron prostheses demonstrated platelet consumption after graft placement (platelet survival 4.2 days +/- 0.5 and turnover 68,000 plat/ul/day +/-10,000 compared with 8.2 days +/- 0.3 and 35,000 plat/ul/day +/- 5,000 respectively for control subjects with stable vascular disease, p < 0.01). In vitro platelet function test results were normal. Platelet consumption was interrupted by dipyridamole or a combination of dipyridamole and acetylsalicylic acid, and platelet survival normalized spontaneously during nine months postoperatively. No significantly increased consumption of fibrinogen or plasminogen was found in these patients with arterial grafts.Placement of impervious knitted Dacron velour aortic grafts in baboons reproduced platelet consumption that progressively normalized over six weeks postoperatively. Platelet survival measurements correlated directly with endothelial cell coverage of the graft luminal surface in these animals implying that endothelialization of the graft surface was also occurring postoperatively in patients.