Comparison between externally stented and unstented PTFE vascular grafts

It has been suggested that external stenting of synthetic vascular prosthetic material may improve patency rates in the low flow situation or across joints. This study compared externally stented polytetrafluoroethylene (PTFE) vascular grafts placed across the hip joint in dogs with nonstented PTFE grafts in regard to patency. Twenty animals underwent bilateral common iliac to common femoral artery bypass with proximal ligation of the femoral artery. In each animal one groin was randomly assigned to receive stented PTFE and the other nonstented PTFE. One animal was sacrificed at 2 weeks for graft infection. Nineteen animals received 38 grafts that remained in place 90-120 days. Patency was confirmed with angiography prior to sacrifice. Overall patency was 65 per cent with no significant difference between the two types of graft. Eighteen of 19 dogs (95%) had both the stented and nonstented PTFE grafts either open or closed. It is concluded that intrinsic factors, rather than external graft support, are a more important influence on graft patency in this model.     

Brachial-jugular expanded PTFE grafts for dialysis

The objective of this study was to analyze the long-term outcome of 51 patients with brachial-jugular grafts for dialysis. Age, presence of diabetic nephropathy, complications of the angio-access, and therapeutic methods of treating complications were analyzed. All surgical procedures were performed under local anesthesia in an ambulatory surgical setting. The duration of angio-access was analyzed using the life-table method. Our results showed that brachial-jugular grafts can be performed under local anesthesia and in an ambulatory surgical setting. This procedure can be an alternative to complex intrathoracic procedures, Dacron cuff catheters, or lower limb grafts, in cases of stenosis or occlusion of the subclavian vein.     

Comparison of expanded PTFE and vein grafts in lower extremity arterial reconstructions

Polytetrafluoroethylene (PTFE) bypasses were used in a series of arterial reconstructions to the popliteal artery (45) and to arteries below that level (11). These were performed in high-risk situations in patients who lacked a suitable saphenous vein. Vein bypasses were performed in a comparable series of high-risk situations in patients having a suitable autologous saphenous vein (45 to the level of the popliteal artery and 11 to an artery below that level). PTFE patency rates at 4-14 months were 43 to 45 (96%) for the femoro-popliteal reconstructions (with a limb salvage rate of 39 to 45 or 87%) and 5 of 11 (45%) for the distal bypasses. Saphenous vein bypass patency rates at 8-14 months were 39 of 45 (87%) for the femoropopliteal reconstructions (with a limb salvage rate of 36 of 45 or 80%) and 5 of 11 (45%) for the distal bypasses. These results justify continued use of PTFE grafts in patients without saphenous veins who require lower extremity arterial reconstructions for limb salvage. The exact place of PTFE grafts in arterial reconstructive surgery of the lower extremity definition based on longer periods of observation.     

Seven-year follow-up of expanded polytetrafluoroethylene (PTFE) femoropopliteal bypass grafts.

Expanded polytetrafluoroethylene (PTFE) grafts have proven to be an acceptable short-term alternative for femoropopliteal reconstruction in those patients without suitable autologous saphenous vein. One hundred and twenty-seven femoropopliteal arterial bypass operations utilizing PTFE grafts were performed in 105 patients. Seven-year follow-up is now available for 20 grafts, 6-year follow-up for 47 grafts, and 5-year follow-up for 62 grafts. Graft occlusion was determined by angiography, Doppler assessment, loss of previously palpable pulses, or return of symptoms. Thirty nonocclusive graft losses were due to death, infection, aneurysm, amputation, or proximal occlusive disease. Overall cumulative patency rate, according to occlusive criteria alone and calculated by the life-table method, was 74% at 6 months, 63% at 1 year, 48% at 3 years, 40% at 5 years, and 35% at 7 years. Excluding early bypass failures (less than 1 year patency), 75% of grafts were patent at 3 years, 63% at 5 years, and 55% patent 7 years following operation. Diabetes mellitus was associated with a significantly lower patency rate. Patency rates were not adversely affected by graft diameter, distal popliteal anastomotic site, number of patent runoff vessels, preoperative symptoms, or prior arterial reconstruction. In patients without suitable autologous saphenous vein, the PTFE graft has proven to be a durable and dependable long-term alternative for femoropopliteal reconstruction.     

The use of covered nitinol stents to salvage dialysis grafts after multiple failures

The increasing number of patients requiring hemodialysis and the limited number of access sites have resulted in an increase in multiple graft revisions to maintain access for hemodialysis. Venous outflow or anastomotic stenoses in vascular grafts tend to recur and contribute to the difficulty in maintaining a functioning graft. Thus, extending the life of a failed graft becomes an important objective of this study, which was to assess the use of covered nitinol stents to salvage expanded polytetrafluoroethylene (ePTFE) grafts with venous anastomotic or outflow stenosis that have failed after multiple revisions. This is a review of 8 failed non-autogenous ePTFE grafts with isolated venous anastomotic or proximal outflow stenoses that had undergone multiple previous revisions, had failed percutaneous transluminal angioplasty (PTA), and required placement of a covered nitinol stent. Graft locations were forearm (2), upper arm (4), and femoral (2). The mean number of interventions per patient before stent placement was 5.87 thrombectomies (range 2-28) and 3.38 balloon angioplasties (range 2-19). Five patients had 0.62 interposition grafting and 3 had patch angioplasty. All 8 patients (100%) underwent successful dialysis after thrombectomy and stenting. The primary and secondary patency rates after stent placement were 50% and 75%, and 25% and 75%, at 3 and 6 months, respectively. Percutaneous thrombectomy, balloon angioplasty, and concomitant covered nitinol stent placement extend the function of hemodialysis access grafts that have previously failed multiple times.     

The influence of node-fibril morphology on healing of high-porosity expanded polytetrafluoroethylene grafts

PURPOSE: To manufacture high-porosity expanded polytetrafluoroethylene (ePTFE) vascular grafts with the same internodal distance but different node-fibril morphology, and to evaluate their biologic behaviors in a canine carotid artery implantation model. MATERIALS AND METHODS: Several types of high-porosity ePTFE vascular grafts with the same inside diameter (4 mm) and wall thickness (650 microm) were manufactured under different heating, stretching conditions. The luminal surface and cross section of the grafts were photographed by scanning electron microscopy and the node-fibril structure was examined. Two typical types of high-porosity ePTFE vascular grafts were then selected and proceeded to an animal study. The test grafts were explanted after an interval of 12 weeks and subjected to histomorphometric analyses. RESULTS: The following two types of high-porosity ePTFE vascular grafts were selected; one had a through-pore structure extending from the outer to the inner surface and the other had a random-node architecture with tortuous path channels extending from the outer to the inner surface. The histomorphometric analyses of thrombus-free surface, thickness of pseudointima, cellular ingrowth, capillary ingrowth, and cellular proliferation revealed no significant differences between the grafts. CONCLUSION: In high-porosity ePTFE vascular grafts, graft healing enhanced by transmural tissue ingrowth may be not largely dependent on node-fibril morphology. This knowledge will be helpful to design a new type of high-porosity ePTFE vascular grafts available for clinical use.     

Enhanced graft healing of high-porosity expanded polytetrafluoroethylene grafts by covalent bonding of fibronectin

(Received for publication on Jan. 5, 1999; accepted on Sept. 17, 1999)     

Transgraft infusion of heparin to prevent early thrombosis of expanded PTFE grafts in canine femoral veins

Recently we designed an expanded polytetrafluoroethylene (ePTFE)-based local infusion device that delivers therapeutic agents directly through the graft wall in the region adjacent to the upstream anastomosis, thereby achieving a high drug concentration downstream along the graft-blood interface. In this study we evaluated the effects of infusing heparin by this method on graft patency and neointimal hyperplasia in a canine model of femoral vein replacement. Five dogs underwent bilateral femoral vein replacement with the device. In each case one graft was infused with continuous heparin (48 U/kg/day) while the contralateral control graft received phosphate-buffered saline solution for 14 days. All heparin-treated grafts were patent and all control grafts were thrombosed at 14 days. There was no significant difference in systemic activated partial thromboplastin time among samples taken preoperatively, at 48 hours, and at 14 days of implantation (p > 0.5). There was no significant difference in neointimal hyperplasia between the upstream and downstream anastomoses in heparin-treated grafts. These data demonstrate that the transgraft infusion of heparin preserved venous ePTFE graft patency without measurable systemic anticoagulation. Thus this approach may represent an attractive strategy for maintaining patency of synthetic venous grafts. Presented at the Twentieth Annual Meeting of the Peripheral Vascular Surgery Society, New Orleans, La., June 10, 1995. Supported in part by research grants HL 31469 and HL 48667 from the National Institutes of Health and by a grant from the American Heart Association.     

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.     

A prospective randomized study of three expanded polytetrafluoroethylene (PTFE) grafts as small arterial substitutes.

A prospective, double-blind, randomized study was performed to determine the relative patency rate of polytetrafluoroethylene (PTFE) grafts, Gore-Tex, Impra, and a Surgikos prototype PTFE graft. The 48 grafts (40 x 4 mm) replaced excised segments of femoral arteries in adult mongrel dogs, whose mean weight was 20.6 +/- 0.9 kg; the grafts were removed after 12 weeks. Sterile technique and antibiotic therapy were included in the study. Anticoagulation was not employed. Anastomoses were performed with 6 = 0 polypropylene. Angiographic assessment of each anastomosis was made at surgery and prior to sacrifice. Patency was assessed daily by palpation and Doppler flow signals, as well as angiographically, prior to sacrifice. The overall patency rate was 62.5%. There were no statistically significant differences in patency rates among the three groups (Gore-Tex, 56%; Impra, 75%, Surgikos, 56%). Histologic evaluation revealed incomplete neointima formation and significant pannus formation in all three types of grafts without any significant discernible difference among them. The results suggest that further experimental evaluation of PTFE, as a small vessel substitute, is indicated prior to its use clinically in preference to autogenous vein.     

Clinical use of microvascular PTFE grafts

This paper reports on the first clinical case where a polytetrafluoroethylene (PTFE) graft of less than 3 mm in diameter was implanted in the arterial system of a patient to bridge a vascular defect. A 1.5 cm long, 1.5 mm diameter prosthesis was interposed in the superficial palmar arch of a man who sustained a laceration of the palm of his dominant hand. The graft was implanted by means of the 3M Precise Microvascular Anastomotic System on one end, and by conventional microsurgical technique on the other end. There were no postoperative complications. The patient resumed his preinjury activities 9 weeks after trauma. Serial Doppler ultrasound examinations showed normal blood flow and complete patency of the graft. An angiogram performed 12 weeks postoperatively confirmed the patency of the prosthesis. Twelve months post-operatively the patient is free from complications. The use of small diameter PTFE prostheses may be considered when planning grafting procedures for microvascular defects. © 1995 Wiley-Liss, Inc.     

A prospective evaluation of plasma-TFE and expanded PTFE grafts for routine and early use as vascular access during hemodialysis.

The use of prosthetic grafts as vascular access for chronic hemodialysis is frequently necessary in patients with end-stage renal disease. Most commonly, expanded polytetrafluoroethylene (e-PTFE) has been employed because of ease of handling, tissue inertness, and acceptable long-term patency. Delay in use to allow for tissue ingrowth, however, has often required placement of temporary access devices. The authors have undertaken evaluation of a new material, plasma polymerized woven dacron Plasma-TFE, in a prospective randomized trial (Plasma-TFE VA) to compare clinical behavior against e-PTFE grafts, and we have used the Plasma-TFE grafts in an additional group of patients (Plasma-TFE AVA) as early access (within 1 week of implantation). Twenty-one Plasma-TFE grafts were implanted in 19 patients and 19 e-PTFE grafts were implanted in 17 patients in a prospective randomized fashion. Additionally, 31 Plasma-TFE grafts were implanted in 31 nonrandomized patients for early access. Primary patency rates in Plasma-TFE VA and e-PTFE grafts were equivalent at 12 months (0.471 and 0.556). When Plasma-TFE AVA primary patency was included (0.621), comparisons were not statistically significant (p = 0.50). Similarly, secondary patency rates among the three groups did not differ (cumulative proportion patent at 12 months: Plasma-TFE VA 0.403, e-PTFE 0.658, Plasma-TFE AVA 0.510). In considering after-revision patency after graft thrombosis, however, the Plasma-TFE grafts (both VA and AVA) performed significantly more poorly (p = 0.027) than e-PTFE grafts. Incidence of graft infection, wound infection, arm edema, hematoma from use, and occurrence of distal limb ischemia between Plasma-TFE (VA and AVA) and e-PTFE did not differ statistically. The authors conclude that Plasma-TFE compares favorably to e-PTFE with respect to primary and secondary patency and nonthrombotic complications, even with early use. Plasma-TFE does not perform as well as e-PTFE, however, after graft thrombosis.     

Comparison of uncovered and covered stents for the treatment of malignant duodenal obstruction caused by pancreaticobiliary cancer

Background

Few clinical studies to date have compared different types of self-expandable metallic stents (SEMS) and their outcomes in patients with pure duodenal obstruction caused by pancreaticobiliary cancer. The aim of this study was to compare the clinical effectiveness and side effects of uncovered and covered SEMS for the palliation of duodenal obstruction caused by pancreaticobiliary cancer.

Methods

We retrospectively analyzed all patients with pancreaticobiliary cancer who underwent upper endoscopy with SEMS placement for malignant duodenal obstruction at the National Cancer Center of Korea between April 2003 and December 2010. The technical and clinical success rates of the procedure, complications, and durations of stent patency and overall survival were evaluated.

Results

We identified 70 patients with a mean age of 51.2 years (range = 39–81 years); of these, 46 (65.7 %) had pancreatic cancer, 9 (12.9 %) had bile duct cancer, 11 (15.7 %) had gallbladder cancer, and 4 (5.7 %) had cancer of the ampulla of Vater. Twenty-four patients (34.3 %) received covered SEMSs and 46 (65.7 %) received uncovered SEMSs. Technical and clinical success rates were similar for the covered and uncovered stent groups. The complication rate was higher in the covered than in the uncovered group (62.5 vs. 34.8 %, P = 0.025), due primarily to a significantly higher stent migration rate (20.8 vs. 0 %, P = 0.004). Perforation as a late complication occurred in four patients, two in each group (8.3 vs. 4.3 %, P = 0.425). Stent patency tended to be shorter for covered than for uncovered duodenal stents (13.7 ± 8.6 weeks vs. not reached, P = 0.069).

Conclusions

The use of uncovered stents may be a preferred option for duodenal obstruction secondary to pancreaticobiliary malignancies, since they were effective in preventing stent migration and tended to have longer patency than covered stents. Careful attention should be paid to signs and symptoms of perforation during follow-up.     

Comparison of polytetrafluoroethylene (PTFE) and dacron as long, small-diameter arterial grafts in dogs

A canine model in which joined carotid arteries were anastomosed to 6-mm grafts (average length, 45 cm) of polytetrafluoroethylene (PTFE) or Dacron double velour and the grafts were anastomosed to the ligated distal abdominal aorta was used to study long-term graft patency. The 16 dogs with PTFE grafts and the 15 dogs with Dacron grafts were sacrificed at three-, six-, and 12-month intervals, or whenever a graft occluded. At three months, eight of 11 PTFE and 11 of 11 Dacron grafts were patent; at six months, two of three PTFE and three of three Dacron grafts were patent; at 12 months, one of two PTFE grafts and the one remaining Dacron graft were patent. All grafts were examined grossly and microscopically. The PTFE grafts showed increasing degrees of calcification and intimal fibrin deposition; the Dacron grafts had no calcification and less intimal fibrin deposition. The model was satisfactory for studying long, small-diameter vascular grafts, but PTFE was not found to be superior to Dacron in this study.