Prosthetic Graft Patency Research Articles

The treatment of failed low limb prosthetic graft bypass for the chronic low limb ischemia: a report of 19 cases

To determine the optimal strategies of occluded prosthetic bypass and to assess the risk factors which influence the outcome. From September 2003 to December 2004, 19 cases of failed low limb prosthetic graft were treated in the Peking Union Medical College hospital. All of them underwent operation, and the strategies of operation were determined by the cause assessed pre-procedure. Four cases underwent thrombectomy only, 5 cases underwent thrombectomy combined with the distal anastomosed-plasty, 3 cases underwent thrombectomy combined with profundaplasty, 2 cases underwent vascular re-construction with new prosthetic graft, 1 case underwent external iliac artery endarterectomy, 2 cases underwent stent cell transplantation, and the last 2 cases underwent amputated since the limbs showed un-salvageable. All the cases got at least 1 year following-up. In the 17 vascular reconstruction cases except the 2 cases who underwent amputated, 14 cases (82.4%) got firstly successes, according to their limb ischemia symptom got well, but the rest 3 cases (17.6%) failed. And the mortality is 10.5% (2 cases). In the 1 year following-up, the prosthetic graft patency was 35.3% (6 cases), and the limb salvage was 76.4% (13 cases). Optimal resolution for prosthetic graft re-occlusion should be based on good judgment of the occlusion cause. Then proper correcting the cause plus right following-up program could be the risk factors of prognosis.

Peptide‐coated vascular grafts: An in vivo study in sheep

The data on function and patency of prosthetic vascular grafts in various clinical settings are limited. The purpose of this in vivo study was to compare the function and patency of P15-coated expanded polytetrafluoroethylene (ePTFE) vascular grafts to uncoated ePTFE grafts in sheep. The P15 cell-binding peptide was covalently immobilized onto the surface of ePTFE grafts by a novel atmospheric plasma coating method. We evaluated the amount of neointimal tissue ingrowth present at the arterial and venous sides of the anastomoses and the degree of endothelial cell resurfacing of the luminal surface of the graft. Four P15-coated grafts and two control grafts were implanted as arteriovenous grafts between the femoral artery and vein and the carotid artery and jugular vein in two sheep (n = 6). One animal was euthanized after 14 days and the other after 28 days. The study showed the intimal ingrowth was significantly less. The average intimal thickness of P15-coated grafts (658 microm) was approximately two and a half times less than that of uncoated samples (1657 microm). The newly formed endothelial cell lining was thicker and its coverage was more uniform for P15-coated grafts compared to the uncoated controls.

Dacron femoral-popliteal bypass grafts in good-risk claudicant patients

Purpose To evaluate prosthetic femoral-popliteal (FP) grafts as bypass conduits in favorable patients with refractory calf claudication. Setting University-affiliated urban teaching hospital. Methods Cohort study of patency of 6-mm Dacron FP grafts used to treat patients with medically refractory calf claudication meeting the following criteria: nonsmoker; above-knee popliteal artery as an appropriate target vessel; ≥2-vessel tibial outflow; and postoperative anticoagulation and antiplatelet therapy. End points included primary and secondary FP graft patency, need for and outcome of subsequent intervention, limb amputation, and survival. Results From January 1998 through March 2001, 92 patients underwent 100 Dacron bypass grafts for medically refractory claudication. All underwent serial postoperative graft surveillance using duplex ultrasound. Using the Society for Vascular Surgery/International Society of Cardiovascular Surgery criteria life-table, primary patency was 84%, assisted primary patency was 88%, and secondary patency was 90% at 5 years. Two patients (2%) died during a mean follow-up period of 49 months (range 30 to 68). No limbs required amputation. Among 9 limbs in which Dacron FP bypass failed, 8 underwent subsequent successful autogenous bypass to the popliteal artery. Conclusion In highly selected subjects with favorable features known to increase the likelihood of prosthetic graft patency, prosthetic FP grafts function well. Such patients undergo a simpler, more straightforward procedure than when autogenous FP bypass is performed. Subsequent success of autogenous FP repeat bypass suggests that previous prosthetic FP bypass does not threaten lower-extremity arterial outflow.

Adjuncts to improve patency of infrainguinal prosthetic bypass grafts.

The superiority of autologous venous conduit for infrainguinal arterial bypass has been well documented, especially when the bypass extends below the knee or to the tibial arteries. Nevertheless, when adequate autologous vein is not available, prosthetic bypasses (eg, polytetrafluoroethylene [PTFE] or Dacron) are often used in limb-salvage situations. The inferior long-term patency of these infrainguinal prosthetic bypasses has been documented by a number of studies. One such study reported a prospective multicenter randomized trial with only a 12% primary patency for infrapopliteal prosthetic bypasses after 4 years. Another study reported a similar experience with infragenicular bypasses with PTFE for limb salvage even for above-knee (27%, 5 year) and below-knee (25%, 5 year) femoral-popliteal bypasses. The reported PTFE graft patency was consistently inferior to that achieved with autologous vein for limb salvage. Dacron grafts appear to have similar patency rates to PTFE. In an attempt to improve prosthetic graft patency, a number of surgical and medical adjuncts have been developed. In this review, the authors discuss these adjuncts and their impact on infrainguinal prosthetic graft patency.

On the Existence of an Optimum End-to-side Junctional Geometry in Peripheral Bypass Surgery—A Computer Generated Study

Background. To investigate hemodynamic flow changes associated with vein cuffs and patches that may be responsible for improved patency of prosthetic infrainguinal grafts. Methods. The role of the graft–artery junction angle was examined by computational fluid dynamics to assess the influence of anastomotic geometry on wall shear stress (WSS) distributions. Three geometrically different junction configurations were studied and the WSS and WSS gradient (WSSG) values were compared. Results. The inclusion of a patch or a cuff moves the bed stagnation point (BSP) distally, increasing the area on the bed of the junction which experiences a BSP and reducing the strength of the recirculation region opposite the heel of the junction by 54.8 and 50.8%, respectively. The patched geometry promotes earlier recovery of the flow in the distal outflow segment (DOS) than for the unpatched model. Also, the helical flow patterns in the DOS associated with the cuffed geometry are stronger. The net effect of these changes are that peak WSSG values for the patched and cuffed geometries are three times lower than those for the uncuffed geometry. Conclusion. This study provides some additional insights into the hemodynamics of graft–artery junction geometry which may influence future clinical practice.

Heparin-coated PTFE graft for aortoiliac bypass grafting inhibits intimal hyperplasia in baboons

Purpose: Intimal hyperplasia and graft thrombosis represent the major causes of graft failure. Heparin has been shown to prolong graft patency and inhibit intimal hyperplasia in animal models. The purpose of the study was to evaluate the effect of a heparin-coated expanded polytetrafluoroethylene (ePTFE) graft in a baboon model of aortoiliac bypass graft placement. Methods: Six adult male baboons (mean weight: 9.3 kg) underwent bilateral aortoiliac bypass grafting with ePTFE grafts (4 mm internal diameter × 5 cm length). In each animal, a heparin-coated ePTFE graft was placed on one side while the contralateral aortoiliac artery received an uncoated graft that served as a control. Platelet counts and activated partial thromboplastin time measurements were performed weekly. The grafts were harvested at 4 weeks and were subjected to morphometric analysis. Cell proliferation was assessed with bromodeoxyuridine immunostaining. Results: All the harvested grafts were patent. No differences were found in platelet counts or activated partial thromboplastin time measurements taken before and after the bypass procedure. There was a significant reduction of neointimal area at both proximal (0.06 ± 0.05 mm2) and distal (0.13 ± 0.07 mm2) anastomoses in the heparin-coated grafts as compared with proximal (0.16 ± 0.07 mm2) and distal (0.33 ± 0.12 mm2) anastomoses in the untreated control grafts (P < 0.05). In addition, neointimal cell proliferation assayed by bromodeoxyuridine (BrdU) incorporation was reduced in both proximal (2.03 ± 0.81%) and distal (3.12 ± 0.14%) anastomoses of heparin-coated grafts compared with proximal (3.54 ± 1.23%) and distal (5.58 ±1.15%) anastomoses of untreated control grafts (P < 0.05). Conclusions: Heparin-coated ePTFE graft significantly reduces anastomotic intimal hyperplasia and cell proliferation without measurable side effects in a baboon model. This approach supports a useful strategy for improving prosthetic bypass graft patency.

In vivo biostability of a poly(carbonate-urea)urethane graft

In peripheral and coronary bypass surgery, the patency of prosthetic grafts is inferior to autologous vein, mainly due to intimal hyperplasia caused in part by compliance mismatch between rigid graft and elastic host artery. We have developed a compliant poly(carbonate-urea)urethane vascular graft “MyoLink™” which was biostable in vitro degradation studies. To further investigate the biostability of this material, we report a long-term in vivo study on 8 beagle dogs (15±3 kg) implanted with this graft (ID 5 mm) in the aorta–iliac position; three grafts were harvested at 18 months to assess short-term biodegradation, with one animal having died from an unrelated infection. The 4 remaining grafts were harvested at 36 months for analysis by: (1) histology, (2) compliance measurements and (3) environmental scanning electron microscopy (ESEM); gel permeation chromatography (GPC); attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and radial tensile strength analysis. There was no infection or inflammation of the grafts or surrounding tissues. Histological analysis showed a well-developed neointima but only at the distal anastomosis. There were no significant differences in compliance pre- and post-implantation and no evidence of material curvature, radial expansion or chemical breakdown, ESEM and GPC showed no signs of degradation. Peak height analysis with ATR-FTIR of the 1740 cm −1 (CO of carbonate) and 1253 cm −1 bands (C–O–C of CO–O–C) showed a loss of carbonate carbonyl but was not statistically significant. Radial tensile strength remained within batch release specifications. This polyurethane graft retains its compliance post-implantation, whilst exhibiting only a minor hydrolysis of the amorphous segment, confirming its biostability in vivo up to 3 years.

Assessment of Prosthetic Vascular Graft Thrombogenicity Using the Technetium-99m Labeled Glycoprotein IIb/IIIa Receptor Antagonist DMP444 in a Dog Model

Introduction: Prosthetic graft patency greatly depends on graft thrombogenicity. The concept of graft thrombogenicity is poorly understood and difficult to measure or quantify. In a study we tested the experimental radiopharmaceutical DMP444 and developed a suitable dog model. This agent is a radiolabelled (99mTechnetium) glycoprotein llb/llla receptor antagonist with a high affinity for activated platelets. It binds to platelets that are intimately involved in thrombus formation. The agent does not affect thrombocyte function, when used in a dose necessary for imaging. DMP444 does not require platelet harvesting and processing. Early imaging of thrombocyte aggregation sites such as vascular prostheses is possible within 4 hours after injection. Material and methods: Adult Beagle dogs weighing 12–15 kg were used for the experiments. In 16 dogs a prosthetic patch was sewn onto the abdominal aorta (Bovine pericard: n= 4, Dacron: n=6. Human Umbilical Vein: n=6). Imaging cycles after injection of 99mTechnetium-labelled DMP444 were performed on days 1,7, 14 and 28 after surgery. Results: We noticed differences in thrombus formation on the tested graft materials. The bovine pericard patches ( n=4) showed a relatively high rate of thrombocyte aggregation. In the Dacron patches ( n=6) aggregation was not seen. In 1 of 6 cases of human umbilical vein patches a measurable focal aggregation was recorded. Conclusion: The method outlined in this study is a relatively simple and reproducable method to visualize thrombocyte aggregation.

Assessment of prosthetic vascular graft thrombogenicity using the technetium-99m labeled glycoprotein IIb/IIIa receptor antagonist DMP444 in a dog model

Introduction: Prosthetic graft patency greatly depends on graft thrombogenicity. The concept of graft thrombogenicity is poorly understood and difficult to measure or quantify. In a study we tested the experimental radiopharmaceutical DMP444 and developed a suitable dog model. This agent is a radiolabelled ( 99mTechnetium) glycoprotein IIb/IIIa receptor antagonist with a high affinity for activated platelets. It binds to platelets that are intimately involved in thrombus formation. The agent does not affect thrombocyte function, when used in a dose necessary for imaging. DMP444 does not require platelet harvesting and processing. Early imaging of thrombocyte aggregation sites such as vascular prostheses is possible within 4 hours after injection. Material and methods: Adult Beagle dogs weighing 12–15 kg were used for the experiments. In 16 dogs a prosthetic patch was sewn onto the abdominal aorta (Bovine pericard: n=4, Dacron: n=6, Human Umbilical Vein: n=6). Imaging cycles after injection of 99mTechnetium-labelled DMP444 were performed on days 1, 7, 14 and 28 after surgery. Results: We noticed differences in thrombus formation on the tested graft materials. The bovine pericard patches ( n=4) showed a relatively high rate of thrombocyte aggregation. In the Dacron patches ( n=6) aggregation was not seen. In 1 of 6 cases of human umbilical vein patches a measurable focal aggregation was recorded. Conclusion: The method outlined in this study is a relatively simple and reproducable method to visualize thrombocyte aggregation.

Development of a hybrid cardiovascular graft using a tissue engineering approach.

Tissue engineering of endothelial cells (EC) and chemical engineering with anticoagulant moieties has been undertaken in order to improve prosthetic graft patency and thrombogenicity. This was done by covalently bonding a compliant poly(carbonate-urea)urethane graft (MyoLink) with arginine-glycine-aspartate (RGD) or/and heparin (Hep) to ascertain whether EC retention could be improved. The retention of these moieties and EC was assessed after exposure to pulsatile flow. We covalently bonded RGD, Hep, and RGD/Hep onto the luminal surface of MyoLink using spacer arm technology. Narrow-beam X-ray photoelectron spectroscopy was carried out to check the efficiency of the bonding. EC were radiolabeled and seeded onto native MyoLink and with 1) RGD-, 2) Hep-, and 3) RGD/Hep-bonded grafts and exposed to shear stress in a physiological flow circuit for 6 h, which reproduces femoral artery flow waveforms and pulsatility. Results were recorded on a gamma camera imaging system. Viability of cells was tested with a modified Alamar Blue assay (ABA) and scanning electron microscopy for morphological appearance of seeded cells. Experiments were repeated (n=6). RGD, Hep, and RGD/Hep were bonded together in a uniform distribution on the luminal surface of each graft type, and bioactivity of each moiety covalently bonded was very high. In the flow circuit, there was exponential cell retention for the first 60 min of flow for all the grafts, but after 6 h of exposure to pulsatile flow the RGD/Hep-bonded graft had a significantly better cell retention rate than native MyoLink (75.7%+/-2.3 vs. 60.5+/-10.1, P<0.05). ABA test showed that all the seeded cells postexposure to flow were viable, and significantly higher metabolic activity was recorded on a RGD/Hep-bonded graft than with MyoLink-seeded graft (P<0.01). Using RGD/Hep covalently bonded onto graft surfaces improves cell retention and provides an antithrombogenic surface for initial blood flow in vivo until full EC activity develops postseeding. This would allow the development and further improvement of hybrid grafts.

Adjunctive techniques to improve patency of distal prosthetic bypass grafts: Polytetrafluoroethylene with remote arteriovenous fistulae versus vein cuffs

The long-term patency for infrapopliteal bypass grafting with prosthetic material is less than optimal. Our experience demonstrates a 40% patency at 2 years for these grafts. Several adjuvant techniques have been developed to improve patency rates, two of which are a remote distal arteriovenous fistula and the creation of a distal vein cuff. This study summarizes our experience with these two techniques. Between 1987 and 1998, 107 bypass graftings were performed to the below-knee popliteal or tibial vessels with the use of polytetrafluoroethylene. One group (48 bypass grafts) had polytetrafluoroethylene with adjuvant distal arteriovenous fistula (DAVF), and a second group (59 bypass grafts) was reconstructed with a distal vein cuff (DVC). The type of bypass grafting that was performed was based on surgeon experience and preference. Indications and demographics were similar in the two groups. All patients underwent the operation for limb-threatening ischemia, including gangrene (DAVF, 23%; DVC, 9%), ulceration (DAVF, 27%; DVC, 51%), and rest pain (DAVF, 50%; DVC, 40%). The primary patency rate was 48% and 38% at 3 years for DAVF and DVC, respectively. Secondary patency was 48% and 47% at 3 years, with limb salvage rates of 76% and 92% for DAVF and DVC, respectively (P <.05). Attempted thrombectomy without continuation of patency was undertaken in two patients with a failed DAVF. Attempts at restoration after thrombosis were made in eight patients with failed DVCs. Five patients underwent thrombectomy, of which four procedures were successful. Three patients had thrombolytic therapy, and two of these remained patent. Adjuvant techniques, including DAVF and DVC, produce acceptable long-term patency and limb salvage rates in bypass grafts performed to the below-knee popliteal and tibial vessels. This study suggests that DVCs may offer improved limb salvage rates and a greater opportunity for revision when bypass graft failure occurs.

Human Endothelial Cell Cultures from Progenitor Cells Obtained by Leukapheresis

Although improved prosthetic graft patency with endothelial cell (EC) seeding has been shown in animal models, the clinical application of this technique requires a convenient source of ECs. We have evaluated EC cultures derived from the mononuclear cell (MNC) fraction obtained during large-volume leukapheresis and compared this with cultures grown from peripheral blood cells obtained by phlebotomy. Leukapheresis was performed in healthy adult volunteers (n = 7) using software designed to increase the percentage of MNCs harvested. Blood (40-293 mL) was drawn from a peripheral vein in healthy adult volunteers (n = 13), and the MNCs were obtained by differential centrifugation using a Lymphoprep gradient. Significantly more MNCs were obtained by leukapheresis than by phlebotomy. Each leukapheresis procedure yielded 12.5 to 23 mL, which contained 2.29 +/- 0.35 x 10(9) MNCs, compared with 2.16 +/- 0.50 x 10(8) MNCs, for each phlebotomy (P < 0.001). EC colonies developed in significantly more cultures from leukapheresis-derived MNCs (6 of 7) than phlebotomy-derived MNCs (4 of 13; P = 0.008). Leukapheresis-derived cells developed EC morphology at 15.5 +/- 2 days compared with 21 +/- 3.4 days for cells obtained by phlebotomy (P = not significant). EC were identified by positive factor VIII and vascular endothelial growth factor receptor immunostaining. Leukapheresis significantly increases the number of progenitor cells available for differentiation into EC compared with phlebotomy and avoids the need for any surgical procedure to harvest a peripheral vein as a direct source of ECs.

Clinical autologous in vitro endothelialization of infrainguinal ePTFE grafts in 100 patients: A 9-year experience

Clinical in vitro endothelialization was assessed for its ability to improve the long-term patency of prosthetic femoropopliteal bypass grafts. Between June 1989 and May 1998, 100 patients received 113 in vitro endothelialized expanded polytetrafluoroethylene grafts (ePTFE). Bilateral implantations were performed in 13 patients. In phase 1 of the study, 24 patients received 27 endothelialized grafts and 16 patients received 17 untreated grafts. In phase 2, endothelialization was offered to all patients who did not have a suitable saphenous vein available. Phase 2 began in June 1993 and included 76 patients who received 86 endotheliazed ePTFE grafts. In all, 100 patients had autologous endothelial cells harvested from 4- to 5-cm segments of a subcutaneous vein. In phase 1, the external jugular vein was used. In phase 2, the cephalic vein was used. These cells were grown to first-passage mass cultures and were lined confluently onto 6-mm ePTFE grafts, pre-coated with fibrin glue. Patency assessment for Kaplan-Meier survivorship analysis was determined by using duplex sonography and angiography. In phase 1, the Kaplan-Meier method revealed a primary 9-year patency rate for 65% for the endothelialized group, versus 16% for the control group (log-rank test, P = .002; Wilcoxon test, P = .003). In phase 2, the 5-year primary patency rate for all in vitro endothelialized infrainguinal reconstructions was 68% (66% for above-the-knee grafts and 76% for below-the-knee grafts). Nine years of clinical in vitro endothelialization provided strong evidence that autologous endothelial cell lining improves the patency of small-diameter vascular grafts and that a cell culture-dependent procedure can be used in a clinical routine.

Clinical autologous in vitro endothelialization of infrainguinal ePTFE grafts in 100 patients: A 9-year experience

Background: Clinical in vitro endothelialization was assessed for its ability to improve the long-term patency of prosthetic femoropopliteal bypass grafts. Methods: Between June 1989 and May 1998, 100 patients received 113 in vitro endothelialized expanded polytetrafluoroethylene grafts (ePTFE). Bilateral implantations were performed in 13 patients. In phase 1 of the study, 24 patients received 27 endothelialized grafts and 16 patients received 17 untreated grafts. In phase 2, endothelialization was offered to all patients who did not have a suitable saphenous vein available. Phase 2 began in June 1993 and included 76 patients who received 86 endotheliazed ePTFE grafts. In all, 100 patients had autologous endothelial cells harvested from 4- to 5-cm segments of a subcutaneous vein. In phase 1, the external jugular vein was used. In phase 2, the cephalic vein was used. These cells were grown to first-passage mass cultures and were lined confluently onto 6-mm ePTFE grafts, pre-coated with fibrin glue. Patency assessment for Kaplan-Meier survivorship analysis was determined by using duplex sonography and angiography. Results: In phase 1, the Kaplan-Meier method revealed a primary 9-year patency rate for 65% for the endothelialized group, versus 16% for the control group (log-rank test, P = .002; Wilcoxon test, P = .003). In phase 2, the 5-year primary patency rate for all in vitro endothelialized infrainguinal reconstructions was 68% (66% for above-the-knee grafts and 76% for below-the-knee grafts). Conclusions: .Nine years of clinical in vitro endothelialization provided strong evidence that autologous endothelial cell lining improves the patency of small-diameter vascular grafts and that a cell culture–dependent procedure can be used in a clinical routine.(Surgery 1999;126:847-55.)

In Vivo Assessment of a Novel Dacron Surface with Covalently Bound Recombinant Hirudin

Prosthetic arterial graft surfaces are relatively thrombogenic and fail to heal with a cellular neointima. The goal of this study was to characterize the in vivo antithrombin properties of a novel Dacron surface with covalently linked recombinant hirudin (rHir) implanted in a canine thoracic aorta with high flow and shear rates. rHir was bound to a knitted Dacron patch using crosslinker-modified bovine serum albumin (BSA) as a basecoat protein. BSA was first reacted with the heterobifunctional crosslinker, sulfo-SMCC. This BSA–SMCC complex was then bound to the carboxylic acid groups of hydrolyzed Dacron patches using the carbodiimide crosslinker, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. Iodinated, Traut’s-modified rHir ( 125I-rHir-SH) was then reacted with the Dacron–BSA–SMCC surface, thereby covalently binding 125I-rHir. Graft segments were washed and sonicated to remove any nonspecifically bound 125I-rHir. Dacron–BSA–SMCC–S- 125I-rHir patches ( n = 5) and control Dacron-BSA patches ( n = 5) were implanted in series in the thoracic aortas of canines. These patches were exposed to nonheparinized, arterial blood flow for 2 hours. Patches were explanted and assessed for 125I-rHir loss. Antithrombin activity of explanted 1-cm 2 patch segments was evaluated using a chromogenic assay with 1, 5, 10, 15 units of added thrombin. Light microscopy was performed to qualitatively examine the pseudointima. Two animals were excluded from the study owing to excessive bleeding through the knitted 125I-rHir patch. Comparison of preoperative and postoperative 125I-rHir γ counts revealed an overall decrease of 20 ± 5.4% over the period studied. Explanted 125I-rHir patch segments were able to inhibit 1, 5, and 7 NIHU of thrombin, demonstrating retained antithrombin activity. Gross and microscopic examination of the control and test Dacron surfaces showed marked differences. Dacron surfaces with covalently bound 125I-rHir had no gross thrombus and a thin pseudointima of platelets and plasma proteins. In contrast, the control patches had a thick pseudointima composed of fibrin-rich thrombus. rHir, covalently bound to Dacron patches, maintains its biologic activity as well as prevents thrombus formation on the graft surface. This novel antithrombin coating, by modifying the blood/graft interface, may improve both short- and long-term patency in small-diameter prosthetic arterial grafts and has applications with respect to other implantable or indwelling biomaterials.

Vascular surgical society of great britain and ireland: duplex surveillance does not enhance infrainguinal prosthetic bypass graft patency

BACKGROUND: All patients discharged from this unit with a patent infrainguinal polytetrafluoroethylene (PTFE) bypass are entered into a graft surveillance programme. Previous internal audit had suggested that duplex surveillance was not worthwhile in this patient group. The aim of this study was to compare the fate of infrainguinal PTFE grafts before and after stopping duplex surveillance. METHODS: Between January 1986 and December 1994, 220 grafts (141 above-knee popliteal, 69 below-knee popliteal, ten tibial) were entered into the duplex surveillance programme. Between January 1995 and June 1996, 56 further grafts (29 above-knee popliteal, 21 below-knee popliteal, six tibial) were followed prospectively without duplex scans. RESULTS: During the first study interval, an 'abnormal' scan was reported in 66 of 220 grafts. For clinical reasons (no further reconstruction feasible), no intervention was undertaken in 56 patients. Of these, 34 grafts occluded and 17 amputations were performed. An intervention to maintain patency was performed in ten patients. In 154 patients with 'normal' scans, 53 grafts occluded and 21 amputations were performed. During the second study interval, 20 grafts occluded and 12 amputations were performed. In six patients, an attempt was made to re-establish patency and this was successful in two. Kaplan-Meier 36-month primary and secondary patency rates were 48 and 51 per cent respectively for the group that underwent duplex surveillance, and 58 and 60 per cent for the group that was followed without duplex imaging. CONCLUSION: Prospective duplex surveillance of infrainguinal PTFE bypass grafts does not enhance graft patency and cannot be justified.

Hemodialysis access: Influence of the human immunodeficiency virus on patency and infection rates

Purpose: The complication rate for patients who are dialysis dependent and infected with the human immunodeficiency virus (HIV) and the role of viral indicators (CD 4 counts) as predictors of these complications are poorly characterized. To determine the influence of HIV status and viral activity on graft patency and infection rates, we retrospectively reviewed our results. Methods: Between June 1993 and March 1997, the charts of 104 patients (HIV+, n = 42; HIV–, n = 62) who required 112 hemodialysis access grafts were reviewed. Of the 112 procedures, 55 (48%) were autologous arteriovenous fistulae (AVF) procedures (HIV+, n = 23; HIV–, n = 32) and 57 (52%) were prosthetic expanded polytetrafluoroethylene grafting procedures (HIV+, n = 27; HIV–, n = 30). Transcutaneous catheter procedures were excluded from the study. The autologous AVF procedures consisted of direct and transposed AVFs. Patency rates were determined by means of life-table analysis. Infection rates and CD 4 counts were compared with the χ 2 test and the Fisher exact test. Significance was accepted at a P value of .05 or less. Results: The cumulative 12-month and 24-month patency rates for prosthetic grafts in patients who were HIV+ were 49% and 21%, respectively, versus 77% and 45% for patients who were HIV–. The differences in the prosthetic graft patency rates between these two groups were significant ( P ≤ .05). The cumulative 12-month and 24-month patency rates for autologous AVF procedures did not differ significantly. The AVF procedure patency rates were 72% and 51%, respectively, in patients who were HIV+ versus 54% and 50% for patients who were HIV–. The prosthetic graft infection rate for patients who were HIV+ and HIV– were 30% and 7%, respectively ( P = .04). However, the infection rates in autologous AVF procedures did not differ between the groups (9% vs 0%; P > .05). The mean CD 4+ cell counts were 174: CD 4+ counts that were less than 200 did not correlate with or predict the development of infection ( P > .05). Conclusion: Our data showed that prosthetic graft infection rates were increased and patency rates were decreased in patients who were HIV+ as compared with patients who were HIV– and HIV+ with autologous AVFs. There were no differences in patency rates or infection rates in patients who had undergone autologous access procedures. Long-term graft patency rates were not affected by HIV status, and CD 4+ lymphocyte counts were not predictive of infection development. Because the prosthetic graft infection rates exceeded those rates of autologous access procedures, we recommend the vigorous use of autologous AVFs in all patients who are HIV+, regardless of CD 4+ count. (J Vasc Surg 1999;29:608-16.)

Vein patching reduces neointimal thickening associated with prosthetic graft implantation

Purpose: Modified anastomotic techniques utilizing autogenous vein-cuffs or patches have been devised with the hope of improving prosthetic graft patency. The mechanisms of the presumed improvement in patched anastomoses have never been elucidated and remain speculative. We characterized the healing response of the Taylor vein patch in prosthetic arteriovenous fistulae in a canine model of intimal hyperplasia. Methods: Six adult dogs underwent placement of bilateral (6 patched, 6 control) 4-mm diameter expanded polytetrafluoroethylene loop femoral artery-vein fistulae. Serial duplex ultrasound examinations confirmed graft patency until explant at 6 weeks. Differential light microscopy with computerized image analysis was performed on serial 5-μm sections. Intimal thickness through the venous anastomosis and outflow veins of Taylor patch and control (nonpatched) grafts were compared. Cell type-specific immunocytochemical antibody stains for smooth muscle cells (α SMC actin) and endothelial cells (von Willebrand factor) were performed. Results: Eleven of 12 grafts remained patent for 6 weeks, 1 control graft thrombosed. Mean duplex-derived peak systolic velocities of patched (96 cm/sec) and control (108 cm/sec) grafts were similar. Microscopy revealed more intimal pannus anastomotic suture line ingrowth in controls (mean thickness = 178 μm) than Taylor patched grafts (mean 147 μm, p = 0.0002). Significantly less intimal thickening was present in the outflow vein of patched (mean thickness = 90 μm) versus control grafts (mean 195 μm, P <0.0001). The intima maintained a single cell layer of vWF + endothelial cells, while the majority of the cells comprising the lesion expressed α SMC actin. Conclusion: Perianastomotic pannus is primarily composed of intimal smooth muscle cells. Neointimal thickening is significantly reduced in prosthetic arteriovenous fistulae created with the Taylor vein patch in a canine model. Reduction in perianastomotic intimal thickening may explain the reported clinical improvement in prosthetic bypass graft patency when modified with vein patch techniques.

Patency of Infrainguinal Polytetrafluoroethylene Bypass Grafts with Distal Interposition Vein Cuffs

Polytetrafluoroethylene (PTFE) prosthetic bypasses in the lower extremity have poor patency rates, particularly in limb salvage cases. Patency and limb salvage rates of PTFE bypasses supplemented by distal interposition vein cuffs were assessed in patients requiring revascularization for critical limb ischemia, in the absence of a suitable autologous saphenous vein. Between October 1993 and April 1996, 163 patients underwent 185 infrainguinal bypasses. Forty-three limbs in 42 patients (12 women, 30 men; mean age 67 years) did not have a suitable autologous saphenous vein (24%) and had femoropopliteal (20) and infrapopliteal (23) bypasses performed. Patients were examined prospectively at 3-month intervals during the first year and at 6-month intervals thereafter to determine graft patency and limb salvage. Postoperative anticoagulation with warfarin was used in 26 patients. Indications for operation included limb salvage in 41 extremities (21 rest pain/ulceration or gangrene, 20 rest pain alone), and disabling claudication in two. Patients were followed clinically for 2–30 months (mean 10 months). Cumulative 2-year life-table patencies for all grafts, femoropopliteal and infrapopliteal bypasses were 64%, 75% and 62%, respectively. Previous primary patencies at the authors' institution for PTFE bypasses without vein cuffs were 35%, 46% and 12% for the same categories. Cumulative life-table limb salvage for all PTFE/vein cuff bypasses in the present series was 76% compared with 37% in previous PTFE bypasses without vein cuffs. Adjunctive use of distal interposition vein cuffs improves prosthetic graft patency, while producing satisfactory limb salvage. Postoperative anticoagulation did not influence graft patency. PTFE/vein cuff for lower-extremity revascularization shows good 2-year patency and is an acceptable alternate conduit in patients with critical limb ischemia when autologous saphenous vein is absent.

Patency of infrainguinal polytetrafluoroethylene bypass grafts with distal interposition vein cuffs

Polytetrafluoroethylene (PTFE) prosthetic bypasses in the lower extremity have poor patency rates, particularly in limb salvage cases. Patency and limb salvage rates of PTFE bypasses supplemented by distal interposition vein cuffs were assessed in patients requiring revascularization for critical limb ischemia, in the absence of a suitable autologous saphenous vein. Between October 1993 and April 1996, 163 patients underwent 185 infrainguinal bypasses. Forty-three limbs in 42 patients (12 women, 30 men; mean age 67 years) did not have a suitable autologous saphenous vein (24%) and had femoropopliteal (20) and infrapopliteal (23) bypasses performed. Patients were examined prospectively at 3-month intervals during the first year and at 6-month intervals thereafter to determine graft patency and limb salvage. Postoperative anticoagulation with warfarin was used in 26 patients. Indications for operation included limb salvage in 41 extremities (21 rest pain/ulceration or gangrene, 20 rest pain alone), and disabling claudication in two. Patients were followed clinically for 2–30 months (mean 10 months). Cumulative 2-year life-table patencies for all grafts, femoropopliteal and infrapopliteal bypasses were 64%, 75% and 62%, respectively. Previous primary patencies at the authors' institution for PTFE bypasses without vein cuffs were 35%, 46% and 12% for the same categories. Cumulative life-table limb salvage for all PTFE/vein cuff bypasses in the present series was 76% compared with 37% in previous PTFE bypasses without vein cuffs. Adjunctive use of distal interposition vein cuffs improves prosthetic graft patency, while producing satisfactory limb salvage. Postoperative anticoagulation did not influence graft patency. PTFE/vein cuff for lower-extremity revascularization shows good 2-year patency and is an acceptable alternate conduit in patients with critical limb ischemia when autologous saphenous vein is absent.