External Velour Research Articles

Endoscopic tunneling of HeartMate II left ventricular assist device driveline

FIGURE 1. The endoscope is introduced into the inferior pump pocket (1) and then tunneled through the muscular abdominal wall (2) to the counterincision (3). After placing the umbilical tape, the endoscope is then placed into the counterincision, and tunneled across the abdomen (4), either below or above the umbilicus, to the driveline exit site (5), which is situated well above the beltline. Current generation ventricular assist devices require a driveline to connect the intracorporeal device to the extracorporeal controller and batteries. Recent experience has suggested anecdotally that a longer subdermal driveline tunnel without any external velour may reduce driveline infections. To accomplish this, a long, sharp C-shaped tunneler traverses the abdominal wall blindly from the right upper quadrant to an exit site on the left upper quadrant. We recently placed a driveline that entered the peritoneal cavity inadvertently while using the standard tunneling technique. As indications for placement of these devices expand to include sick and elderly patients, more patients will have had previous abdominal incisions and/or cachexia with little preperitoneal or subdermal adipose tissue. These factors can make blind placement of drivelines more hazardous. Therefore, we developed a simple, cost-effective technique using our current endoscopic saphenous vein harvesting system that allows direct visualization and safe placement of the driveline. We report this experience after receiving approval from the Cleveland Clinic’s institutional review board.

In Vitro and In Vivo Characterization of a Silk Fibroin‐Coated Polyester Vascular Prosthesis

Silk fibroin (SF) is well known to be biocompatible, degradable, and nontoxic. In this study, SF was impregnated into a porous polyester graft (InterVascular external velour, InterVascular, Inc., La Ciotat, France), 8 mm in diameter. The SF-impregnated graft was investigated in vitro and in vivo to evaluate its potential for use as a new vascular graft impervious to blood, while retaining high porosity for tissue ingrowth and biological healing. For in vitro investigation, the water permeability, coating weight, morphology, and mechanical properties of the SF-impregnated grafts were compared with collagen-coated grafts (InterGard grafts, InterVascular, Inc.). The water permeability of the controls (1388 +/- 30.5 mL/cm(2)/min at 120 mm Hg) was reduced >99% by SF impregnation, rendering the graft impervious to blood. The coating weight of the collagen was 117 +/- 22 mg/g of graft, producing a slightly lower value than the InterGard prosthesis (302 +/- 23 mg/g). For the in vivo experiment, six SF-sealed vascular grafts were implanted in the abdominal aorta of dogs for scheduled periods ranging from 4 h to 6 months. Commercial collagen-impregnated grafts (InterGard) and untreated external velour grafts (InterVascular) were also implanted for scheduled periods ranging from 1 to 6 months for comparison. Gross observation of the explanted grafts and histological examination of the representative sections were conducted for two types of grafts using a light microscope after hematoxylin-eosin staining. These SF-impregnated grafts showed less foreign body and inflammation reactions, and the SF layer was almost completely absorbed. The average of the values in each period for the SF grafts was 48% neointima at 1 month, 85% at 3 months, and 97% at 6 months, whereas those of the InterGard prostheses was 34, 46, and 90%, respectively. This study demonstrated that the use of a biodegradable SF as biological sealant can be a feasible approach to prepare impervious textile arterial prostheses. The SF-impregnated graft showed less thrombogenesis and induced host cell migration along the matrix without foreign body or inflammatory reactions. Moreover, it appears to facilitate the development of endothelial-like cells.

Experimental study of a new tracheal prosthesis: Pored Dacron tube

Objective This study was designed to evaluate how various sizes and densities of pores in Dacron tubing might enhance its utility as a tracheal prosthesis. Methods A vascular prosthesis made of knitted external velour polyester was prepared for pore formation with a laser. The first set compared different pore sizes (300, 500, and 700 μm) and pore densities (25/cm 2 or 100/cm 2). Grafts were reinforced with an externally heat-sealed silicone ring. The second set tested grafts with a pore density of 64/cm 2 and a pore size of 500 μm internally reinforced with a stainless-steel spiral stent. In all experiments, a canine mediastinal trachea 10 cartilage rings in length was resected, and the prosthesis was then implanted with an omental flap. Results Lower pore size and density (300 μm, 25 pores/cm 2) led to essentially no tissue ingrowth. Larger pore size (700 μm) and low density (25 pores/cm 2) led to rapid and excessive ingrowth of granulation. Midrange pore size (500 μm) and high density (100 pores/cm 2) invited steady tissue ingrowth, but marked luminal stenosis eventually developed. Stent-reinforced prostheses with 500-μm pores at 64 pores/cm 2, as used in the second set, maintained an average patency rate of 60% or more (range, 20%-100%) at least 12 months after implantation. Conclusion Our data show that porosity is a key factor for tissue growth through our Dacron tracheal prostheses. This artificial trachea model has led to long-term survivors up to 27 months after the operation and seems promising as a basic model for clinical tracheal repair.

Multiple Nonanastomotic Aneurysms in an External Velour Ringed Dacron Femoropopliteal Vascular Prosthesis

Nonanastomotic aneurysms of arterial prosthetic grafts are an infrequent but well-documented complication of arterial bypass surgery. Several cases of nonanastomotic aneurysm formation of the external velour-type Dacron graft have been reported. We present a case of an external velour ringed Dacron (Sauvage EXS) femoropopliteal bypass graft with multiple nonanastomotic aneurysms. An extensive review of the English literature shows this to be the first reported case of multiple aneurysms occurring in this type of prosthesis.

Factors contributing to success and failure of femorotibial bypass grafts.

AbstractFemorodistal bypass grafting is an important technique in the armamentarium of vascular surgeons, and it has been found that the cost of such procedures justifies their performance in patients who have sustained critical ischemia. Graft material remains the most important factor in causation of graft failure, with all prosthetics having disadvantages when compared to the saphenous vein. In attempts to use biological materials, both bovine heterografts and human umbilical vein grafts have been seen to form aneurysms and undergo thrombosis. Meanwhile, many variations on the theme of prosthetic grafts have been tried and found wanting when used as bypasses from the femoral artery to the distal circulation. Among configurations tried have been polytetrafluoroethylene with and without external support; Dacron® in woven and knitted format, with or without internal and external velour; and combinations of these. As patency rates of these reconstructions have proven inferior to others using the saphenous vein, attempts have been made to extend the use of autogenous biologic material. Such attempts have included cephalic vein bypass grafts, short vein bypass grafts originating distal to the femoral artery, deep veins used as grafts, and the in situ bypass. Lately, it has been recognized that the in situ bypass, when compared to concurrent controls, shows no significant advantage to the popliteal level but is the technique of choice when distal anastomoses are at or distal to the midcalf. Compositesequential bypasses represent another technique developed to utilize the autogenous vein as a distal segment. While this has increased the rate of patency of distal bypass grafting, other aids to patency such as use of anticoagulants, antiplatelet agents, and adjunctive arteriovenous fistula have not. Dynamics of the coagulation system show an intrinsic change in patient status toward coagulation in the postoperative period, and although this factor is of some significance in causing early graft thrombosis, technical defects do not seem to play an important part. This review details some of these important causes of graft failure and places them in proper perspective.

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.

Influence of prosthetic graft fabrication on graft healing, I

The object of this report was to analyze graft healing by comparing the content of collagen and noncollagen protein among seven commonly used prostheses: light-weight knitted dacron concentric crimp (USCI), Sauvage filimentous external velour knitted dacron with concentric crimp, random crimp, or no crimp (USCI), microvel double-velour knitted dacron concentric crimp (Meadox), PTFE Impra, and PTFE Gortex. Grafts (6 mm) were used to replace 4-cm segments of infrarenal abdominal aorta in 85 experimental dogs and five autograft aorta control animals. At 3 and 6 months postimplantation the grafts were aseptically harvested, inspected for completeness of neointimal healing and submitted for biochemical analysis. After 3 months implantation, uncrimped external velour grafts had less hydroxyproline than all dacron grafts except random crimp external velour ( P < 0.05) but not less than both PTFE grafts and most dacron and PTFE grafts were not significantly different in noncollagen protein. After 6 months implantation, all dacron grafts had more hydroxyproline than both PTFE grafts ( P < 0.03) and most dacron grafts had significantly more noncollagen protein than PTFE Impra ( P < 0.05). Of all the grafts analyzed, only uncrimped external velour knitted dacron grafts had both rapid neoendothelial healing and a significant increase in both hydroxyproline and noncollagen protein between 3 and 6 months after graft implantation ( P < 0.01). These data indicate that dacron prostheses heal in a manner different from that of PTFE grafts, that there may be differences among the various types of dacron prostheses, and that external velour uncrimped grafts would appear to have the best healing characteristics.

Graft Infection or Graft Reaction?

A perigraft reaction has been described that has been found to be free of infection, with a microscopic picture compatible to an immunologic-like reaction. Varied time intervals between onset of reaction and removal of tissue have allowed for a histopathologic staging. Note is made that four of the five grafts involved were external velour Dacron, with a question remaining as to whether the double velour stimulates an intensified hyperimmune response. Graft replacement by way of new uninvolved plains of tissue has not been necessary. Replacement with polytetrafluoroethylene through the same pathway resulted in prompt healing of wounds with no evidence of recurrent reaction.

A Comparison of Rapid-Healing Prosthetic Arterial Grafts and Autogenous Veins

The patency rates and healing characteristics during a nine-month period of internal velour Dacron grafts, external velour Dacron grafts, and Sparks-Mandril grown grafts were compared with autogenous jugular veins when used to bypass short segments of the canine femoral artery. Graft thrombosis occurred in three of 11 external velour grafts, in six of 11 internal velour grafts, and in three of 11 Sparks-Mandril grafts, None of 33 autogenous veins occluded. Graft thrombosis was not correlated with the degree of graft healing but rather with a hyperplastic proliferative intimal lesion observed at the proximal anastomosis of the occluded grafts.

Seeding Endothelium Onto Canine Arterial Prostheses

To identify prosthetic characteristics that support the proliferation of an endothelial lining, 14 different graft designs were studied in dogs. The grafts were prepared by the use of a technique of endothelial seeding that we described previously. They were studied two and four weeks after their implantation. Weft-knit Dacron grafts (water porosity from 1,400 to 1,650 mL/min/sq cm) were the most successful. A velour index (velour stitch frequency times velour loop height) was computed. When the internal velour index (IVI) was greater than 60,000 loop-mu/sq cm, the percentage of clot-free surface was 17.2 +/- 14.5%, compared with 62.0 +/- 26.9% when the IVI less than 60,000 loop-mu/sq cm. Endothelium could be detected on 61.5% of the grafts when the IVI less than 60,00 loop-mu/sq cm, compared with 0% when the IVI greater than 60,000 loop-mu/sq cm. The cells that formed the outer capsule were better organized and more adherent to the graft when an external velour was present, but external velour did not affect the inner lining. We conclude that weft-knit Dacron grafts with water porosities from 1,400 to 1,650 mL/min/sq cm and with limited internal velour (IVI less than 60,000 loop-mu/sq cm) are suitable substrates for single-staged endothelial-cell seeding.

Bacteremic infectability: A function of vascular graft material and design

Ninety female mongrel dogs had their infrarenal adbominal aortas alternately replaced with ultralightweight Dacron, expanded Teflon, or external velour Dacron grafts. The grafts were left in place for either 3 or 6 months, challenged with an intravenous infusion of Staphylococcus aureus, and then retrieved. 1. 1.|Gross examination showed that the external velour grafts were most frequently lined at 3 months. At 6 months the velour and Teflon grafts were lined significantly more frequently than the ultralightweight graft. 2. 2.|Microscopic examination reveals that the velour grafts are cellularly healed more frequently at 3 months than the other two grafts. At 6 months the velour and Teflon grafts were more frequently healed than the ultralightweight Dacron; however the cellular lining of the teflon grafts was very thin compared to that of the velour and ultralightweight grafts. 3. 3.|The infection rates at 3 months were: velour, 50%; Teflon, 50%; and ultralightweight, 80%. At 6 months the rates were: velour, 20%; Teflon, 40%; and ultralightweight, 60%. We conclude that the velour graft is most resistant to infection of bacteremic origin because of its tendency to heal more quickly and completely.

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.