Intermediate Outcome and Risk Factor Assessment of Bovine Vascular Heterografts used as AV-Fistulas for Hemodialysis Access

Polytetrafluoroethylene and Bovine Mesenterial Vein Grafts for Hemodialysis Access: A Comparative Study

Purpose

This study aimed to evaluate the safety and patency rate of bovine mesenterial vein grafts (BMVG) for vascular access (VA) in hemodialysis patients (HDP), compared to expanded polytetrafluorethylene (ePTFE grafts) over a mid- to long-term period.

Methods

Patency and complication rate of 23 consecutive HDP with BMVG for VA were compared to a control group consisting of 23 similar HDP with ePTFE grafts. In both groups, the graft was placed preferably in a forearm loop configuration. The same surgeon performed all procedures. All patients were followed over a period of 4 yrs.

Results

Graft placement was successful in all patients. Patency rates did not differ significantly in both groups. However, there were less severe complications in the BMVG group.

Conclusion

The BMVG is a viable alternative for HD access in patients where autologous construction is not possible, and should be given priority in patients with a failed ePTFE graft or high risk for infection.

Operative and perioperative management of infected arteriovenous grafts

Vascular graft infections are a particularly troublesome complication for dialysis patients, many of whom are in an already immunocompromised state. The objective of this review is to detail the risk factors, etiology, diagnosis, perioperative and operative management of vascular graft infections.

Long-Term Results of Biological Grafts for Haemodialysis Vascular Access

The quest for suitable conduits for dialysis access has continued since the first patients were dialysed. Whilst synthetic grafts made from expanded polytetrafluoroethylene (ePTFE) have been the main definitive option after autologous arteriovenous fistulas they have a number of drawbacks, which has led to the use and development of biological grafts such as autografts, homografts or xenografts. Technology continues to improve and currently biosynthetic options are available which may combine the benefits of a readily available product without the drawbacks of PTFE. The history and evidence of biological options for haemodialysis access are discussed.

Engineering of biomimetic nanofibrous matrices for drug delivery and tissue engineering

Biomimetic nanofibers have emerged as promising candidates for drug delivery and tissue engineering applications. In this paper, recent advances on the fabrication and application of biomimetic nanofibers as drug carriers and scaffolding materials are reviewed. First, we delineate the three popular nanofiber fabrication techniques including electrospinning, phase separation and molecular self-assembly, covering the principal materials used for different techniques and surface functionalization strategies for nanofibers. Furthermore, we focus our interest on the nanofiber-based delivery strategies and underlying kinetics for growth factors and other bioactive molecules, following which we summarize the recent advances in the development of these nanofibrous matrices for bone, vascular and neural tissue engineering applications. Finally, research challenges and future trends in the related areas are discussed.

Results of a seven-year, single-centre experience of the long-term outcomes of bovine ureter grafts used as novel conduits for haemodialysis fistulas

PURPOSE

To report the long-term outcomes of bovine ureter grafts as novel conduits for haemodialysis fistulas.

MATERIALS AND METHODS

Thirty-five patients underwent placement of a total of 40 SynerGraft 100 (SG100; CryoLife Europa(®), Guildford, UK) bovine ureter grafts between April 2002 and February 2009. Prospective data were collected on all patients, including active surveillance with blood flow studies and 6-monthly duplex ultrasound studies. Main outcome measures were primary and secondary patency rates.

RESULTS

Mean follow-up time was 97 weeks (range 4-270). Thirteen patients died from unrelated causes during the study period; 12 of these patients had a functioning graft at the time of death. Five patients underwent transplantation, and all had a functioning graft at transplantation. Twelve patients had a functioning graft at the end of the study period. One hundred and ten stenoses were detected, and 97 venoplasty procedures were performed. Of the stenoses, 41.8% were located at the venous anastomosis, 12.7% within the graft, 17.3% in the outflow veins, and 28.1% in central veins. No arterial stenoses were detected. Primary patency rates were 53% at 6 months and 14% at 1 year. Secondary patency rates were 81% at 6 months, 75% at 1 year, and 56% at 2 years.

CONCLUSIONS

Active surveillance and intervention was able to achieve satisfactory long-term secondary patency for these novel conduits compared with those made of PTFE seen in other studies [1].

The use of three-dimensional nanostructures to instruct cells to produce extracellular matrix for regenerative medicine strategies

Synthetic polymers or naturally-derived extracellular matrix (ECM) proteins have been used to create tissue engineering scaffolds; however, the need for surface modification in order to achieve polymer biocompatibility and the lack of biomechanical strength of constructs built using proteins alone remain major limitations. To overcome these obstacles, we developed novel hybrid constructs composed of both strong biosynthetic materials and natural human ECM proteins. Taking advantage of the ability of cells to produce their own ECM, human foreskin fibroblasts were grown on silicon-based nanostructures exhibiting various surface topographies that significantly enhanced ECM protein production. After 4 weeks, cell-derived sheets were harvested and histology, immunochemistry, biochemistry and multiphoton imaging revealed the presence of collagens, tropoelastin, fibronectin and glycosaminoglycans. Following decellularization, purified sheet-derived ECM proteins were mixed with poly(epsilon-caprolactone) to create fibrous scaffolds using electrospinning. These hybrid scaffolds exhibited excellent biomechanical properties with fiber and pore sizes that allowed attachment and migration of adipose tissue-derived stem cells. Our study represents an innovative approach to generate strong, non-cytotoxic scaffolds that could have broad applications in tissue regeneration strategies.

Randomized clinical trial comparing decellularized bovine ureter with expanded polytetrafluoroethylene for vascular access

BACKGROUND

The SynerGraft model 100 (SG 100) is a decellularized bovine uereter graft developed to improve on prosthetic conduits for vascular access. Its clinical performance was compared with polytetrafluoroethylene (ePTFE) in a prospective, pilot randomized study.

METHODS

Patients requiring haemodialysis with no native vein options were included. Between June 2004 and June 2007, 29 patients received SG 100 and 27 ePTFE grafts. Forty-five patients had undergone previous access surgery. All grafts were between the brachial artery and the axillary vein.

RESULTS

Clinical details were similar between the groups; overall mean(s.d.) follow-up was 469(398) days. After 1 year, there were no significant differences in primary patency (28 per cent for SG 100 versus 48 per cent for ePTFE; P = 0.290), assisted primary patency (52 versus 64 per cent; P = 0.430) or secondary patency (57 versus 68 per cent; P = 0.370). Freedom from infection at 1 year was 96 per cent for SG 100 and 91 per cent for ePTFE (P = 0.410). Fifty-seven further procedures (18 endovascular and 39 surgical) were needed to maintain patency in 50 grafts (23 SG 100 and 27 ePTFE).

CONCLUSION

Both grafts were adequate conduits for haemodialysis and were amenable to repair. Anticipated advantages for SG 100 were not seen in either patency or stability.

Neointimal hyperplasia associated with synthetic hemodialysis grafts

Stenosis is a major cause of failure of hemodialysis vascular grafts and is primarily caused by neointimal hyperplasia (NH) at the anastomoses. The objective of this article is to provide a scientific review of the biology underlying this disorder and a critical review of the state-of-the-art investigational preventive strategies in order to stimulate further research in this exciting area. The histology of the NH shows myofibroblasts (that are probably derived from adventitial fibroblasts), extracellular matrices, pro-inflammatory cells including foreign-body giant cells, a variety of growth factors and cytokines, and neovasculature. The contributing factors of the pathogenesis of NH include surgical trauma, bioincompatibility of the synthetic graft, and the various mechanical stresses that result from luminal hypertension and compliance mismatch between the vessel wall and graft. These mechanical stimuli are focal in nature and may have a significant influence on the preferential localization of the NH. Novel mechanical graft designs and local drug delivery strategies show promise in animal models in preventing graft NH development. Successful prevention of graft stenosis would provide a superior alternative to the native fistula as hemodialysis vascular access.

Incomplete cellular depopulation may explain the high failure rate of bovine ureteric grafts

BACKGROUND

The aim was to assess the results of a decellularized bovine ureter graft (SynerGraft) for complex venous access.

METHODS

Bovine ureter conduits were implanted in patients with a failed fistula or access graft in whom native vessels were unsuitable as conduits. Graft histories were obtained from all patients who had undergone this procedure at one institution. Failed grafts were explanted and subjected to histological examination. A sample of fresh bovine ureter was immunostained for galactose (alpha1 --> 3) galactose (alpha-Gal).

RESULTS

Nine patients with a median age of 46 (range 25-70) years underwent complex venous access surgery between August 2004 and November 2006 using a SynerGraft. Graft types included loop superficial femoral artery to stump of long saphenous vein (four patients), loop brachial artery to vein (two), brachial artery to axillary vein (two) and left axillary artery to innominate vein (one). Three grafts developed aneurysmal dilatation and two thrombosed. Histological assessment of the explanted bovine ureters revealed acute and chronic transmural inflammation. Immunostaining of fresh bovine ureter suggested residual cells and the xenoantigen alpha-Gal.

CONCLUSION

Graft failure with aneurysmal dilatation and thrombosis in complex arteriovenous conduits using bovine ureter may be due to residual xenoantigens.

Diagnostic imaging of and radiologic intervention for bovine ureter grafts used as a novel conduit for hemodialysis fistulas

OBJECTIVE

The objectives of our study were to review the appearances on diagnostic imaging and amenability to imaging-guided intervention of a novel bovine ureter graft (Syner-Graft 100 [SG 100]) for use as a conduit for hemodialysis fistulas.

CONCLUSION

The SG 100 shows initial promise as a conduit for hemodialysis fistulas in patients with difficult vascular access. The SG 100 has characteristic appearances on diagnostic imaging and is prone to similar pathologic processes that affect autogenous venous and synthetic grafts. These grafts are readily amenable to imaging-guided percutaneous intervention, which plays a major role in prolonging graft function.

Grafts and graft materials as vascular substitutes for haemodialysis access construction

Apart from long-term central venous catheterisation, the insertion of an arteriovenous graft (AVG) remains the only option to allow continued haemodialysis when the patient's superficial veins have been exhausted. Although, expanded PTFE has become the graft of choice for haemodialysis access throughout the world, many other organic or semi-organic materials are currently available for AVG construction. These are less prone to steal syndrome, easier to handle, more resistant to infection and may have similar, if not better, long term patencies.

Depopulated bovine ureteric xenograft for complex haemodialysis vascular access

OBJECTIVES

To assess performance of a de-cellularised bovine ureter vascular graft for haemodialysis in patients for whom conventional access was not possible.

METHODS

The Syner Graft Vascular Graft Model 100 (SGVG 100) is a bovine ureter modified by a tissue-engineering depopulation technology and uniquely it is not chemically cross-linked. SGVG 100 was implanted in patients with a failed fistula or vascular access grafts. Graft patency was the primary outcome; secondary outcomes included adverse events and associated treatments.

RESULTS

25 SGVG 100 were implanted in 23 patients; mean age was 59+/-14 years. Mean follow-up was 370 days. The mean time to occlusion (19 events) was 215+/-141 days with patency re-established in 14 of 18 surgical interventions. Thirty angioplasties were performed on 14 SGVG 100 for luminal/anastomotic stenosis. Two grafts demonstrated areas of dilation; however, both grafts continue to be usable at last reported follow-up (930 and 602 days) with no further changes in graft size. Primary patency, assisted primary patency, secondary patency, and freedom from infection were 29, 45, 81, and 95% at 1 year, respectively.

CONCLUSIONS

This report demonstrates SGVG 100 is a stable vascular access conduit, providing a suitable graft alternative when autologous vein is not available.

Midterm Results with the Use of Polycarbonate Urethane Heterografts for Dialysis Access

Dialysis access surgery is currently one of the most common vascular operations as the dialysis patient population increases. Although autogenous arteriovenous fistulae stand as the preferred method of access due to excellent patency and lower complication rates, grafts may provide alternative approaches when an autogenous fistula is impractical usually due to depleted veins. We aimed in this study to assess early and midterm outcome with the use of Expedial heterografts (LeMaitre Vascular Ltd., Wrexham, UK) for angioaccess between October 2000 and December 2004. Patients were prospectively followed for pre- and peri-operative course with 1st, 6th and 12th month outpatient controls for patency and complication rates. A total of 34 heterografts were implanted in 30 patients (22 males and 8 females; median age 60.6 years, range 32 - 70). The mean followup for 30 patients were 16.3 +/- 6.1 (range 4 - 30) months. 28 grafts (82.4%) were placed in forearm position. Primary and secondary patencies were found as 81% and 94%, respectively (p = 0.15), with the median censored primary and secondary patencies of 27 +/- 1.7 months (95% CI, 23.38 to 30.67) and 30.42 +/- 1.1 months (95% CI, 28.30 to 32.54), respectively. Only presence of diabetes was found as a significant risk factor in the regression model (p = 0.01). We suggest that the polycarbonate urethane heterografts with acceptable patency/complication rates and shorter maturation times for dialysis access serve an alternative for these patients.