Arteriovenous Fistula Construction with the VasQ™ External Support Device: A Pilot Study

Comparative effectiveness of arteriovenous fistulas created with a nitinol extravascular support in patients with advanced kidney disease

BACKGROUND

Use of a nitinol extravascular support implanted during AVF (arteriovenous fistula) creation has been gaining traction due to its potential to improve functional success and reduce interventions; however, comparative effectiveness data with traditional unsupported AVFs are lacking. The objective of this study was to compare outcomes of AVFs created with a vascular support device versus traditional unsupported AVFs in patients with advanced kidney disease.

METHODS

This was a comparative effectiveness retrospective observational cohort study conducted using data from the prospective, multi-center, single-arm VasQ US Pivotal trial (extravascular support AVF group) matched with an unsupported AVF control group developed using Medicare claims data from the same surgeons that participated in the trial. Eligible control participants were Medicare fee-for-service beneficiaries who underwent AVF creation (2017-2019). Endpoints included 6-month primary patency (primary endpoint), intervention rate, and functional success. Propensity score methods using inverse probability treatment weighting were used to examine the association between supported device use and outcomes.

RESULTS

A total of 782 unsupported AVF patients were compared to the 144 supported AVF patients from the Pivotal study. Compared with unsupported AVFs, primary patency at 180 days was superior for supported AVFs (66% vs 36% for control; OR, 3.27; 95% CI, 2.15-5.17; p < 0.0001). Intervention rate for supported AVFs (0.97 per patient-year; 95% CI, 0.71-1.28) was nearly half of unsupported AVFs (1.91 per patient-year; 1.58-2.07; p < 0.0001). Functional success for supported AVF patients was significantly greater than unsupported AVFs at 90 days (43.4% vs 26.7%, respectively; p = 0.005) and 180 days (72.5% vs 53.7%, respectively; p = 0.004).

CONCLUSIONS

AVFs created with extravascular support maintained higher primary patency, improved functional success, and had less reinterventions than unsupported AVFs. More patients may begin using their AVF for dialysis sooner with a lower risk of requiring a maturation procedure if created with extravascular support.

Efficacy and safety of implantable vascular support in the treatment of arteriovenous fistula: A single-arm meta-analyses

BACKGROUND AND OBJECTIVES

VasQ (Laminate Medical Technologies, Israel) is an external support device for autologous arteriovenous fistula (AVF) designed to improve anastomotic blood flow and reduce neointimal hyperplasia. However, different studies have shown that the efficacy of the VasQ device in improving AVF is inconsistent. The purpose of this study was to conduct a meta-analysis to further evaluate the efficacy and safety of the VasQ device.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Two reviewers independently searched studies published in PubMed, EMBASE, Cochrane, Web of Science, CNKI, and Wan Fang databases from inception to 2023. The Cochrane Systematic Evaluation Bias Risk Tool Version 1 was used to assess the risk of RCTS bias. The ROBINS-I tool was used to assess the risk of bias in non-randomized studies. A Single-arm meta-analysis was performed, and a random effects model was used for all analyses.

RESULTS

We identified six trials involving 146 patients and conducted a meta-analysis. The results showed that after 6 months of VasQ device treatment, the primary patency rate of AVF was [76.4% (95%CI: 0.608-0.920), p < 0.01] while the secondary patency rate was [76.5% (95%CI: 0.572-0.958), p < 0.01]. The maturity rate of AVF 1 month after surgery was [88.5% (95%CI: 0.818-0.952), p = 0.46]. The incidence of anastomotic stenosis was [8.9% (95%CI: 0.015-0.163), p = 0.23], and the incidence of anastomotic venous thrombosis was [10% (95%CI: 0.035-0.179), p = 0.38].

CONCLUSIONS

Meta-analysis data of this study show that the VasQ device has a good effect in improving the patency rate of AVF and does not increase the occurrence of adverse events. However, due to the limitation of the number and quality of included studies, more high-quality studies are needed to confirm this in the future.

International survey of radiocephalic arteriovenous fistula: ISRAF survey

AIMS

The objective of this survey was to encompass the full scope of international practice, entailing all technical, non-technical, preoperative stratification and functional maturation (FM) of RCAVF.

METHODS

The survey contained n = 19 questionnaires with n = 46 variables completed by n = 85 providers from n = 21 nations across n = 5 continents. The numerical values were subjected to mean with standard error whereas the nominal data to a non-parametric (Kruskal-Wallis & Spearman correlation test) and analysis of variance (ANOVA). The test of homogeneity, & probability was reported 95% confidence intervals (CI) alongside error plots. Furthermore, a decision and higher attribute tree model was constructed based on current survey for higher FM in RCAVF.

RESULTS

FM is independently associated with volume of surgeon per year (procedures performed) (p < 0.01) [High Volume: 73% (95% CI, 68-77%) versus Average volume: 63% (95% CI, 59-66%) vs Low volume: 56% (95% CI, 51-61%)]. FM increased by 8% with every 20 more procedures per group of surgeons on end point of FM. Amongst continents: Australia, America, Asia and South America demonstrated higher FM to Africa & Europe (p < 0.05). UK possessed a lower FM 58% (95% CI, 48-68%) in comparison to the world & Europe respectively [65% (95% CI, 61-70%) vs 61% (95% CI, 58--65%)]. There was a positive causal link between angle of anastomosis at 30-76° (p < 0.01), longitudinal & S-shaped incision & arteriotomy length of 3 & 4 mm to higher FM (p < 0.05).

CONCLUSION

FM in RCAVF is independently & incrementally associated with the volume of surgeon per year. There is a diverse inclusion, exclusion and technical approach in RCAVF creation. This survey advocates the importance of international collaboration and/or registry in assimilation, consolidate and development of consensus.

Safety and efficacy of an innovative external support device for de novo arterio-venous fistula creation: a French bicentric experience

BACKGROUND

The aim of this study was to evaluate the safety and efficacy of VasQTM, a permanent extravascular nitinol vascular support device, implanted around the anastomosis of de novo arteriovenous fistulas (AVF), in consecutive patients.

METHODS

This was a French prospective bicentric study. All patients with an indication for creation of a distal or proximal end to side AVF performed by supervised trainee were eligible. Follow-up was performed clinically and by Duplex scan at 6 weeks and 6 months post fistula creation. Primary endpoint was functional maturation at 6 weeks defined as successful use for dialysis via 2-needle cannulation in dialysis patients or a flow rate of ≥600 mL/min and a target vein diameter ≥6 mm for pre-dialysis patients. Overall functional success for dialysis patients was assessed as well.

RESULTS

Between March and November 2022, 21 patients received the VasQTM device and were followed for an average of 165 days. Median age was 61. Eleven patients (52%) were on dialysis at the time of implantation. AVFs were created with distal radial (N.=8), proximal radial (N.=5), brachial cephalic (N.=4) or brachial basilic (N.=4) arteries with 100% technical success . Functional maturation at 6-weeks was achieved in 81% (17/21). Functional success was 80% (12/15) with unassisted functional success of 67% (10/15) at 6 months for patients requiring dialysis at that time point. Two reoperations were performed within the device, one thrombectomy and one angioplasty, both were successful. Freedom from access-related interventions occurred in 71% (15/21) of the study population at 6-months.

CONCLUSIONS

This study demonstrates that the VasQTM AVFs achieved high rates of maturation at 6-weeks, without the need to modify standards of care. VasQTM can successfully assist in achieving excellent results at the introduction of the device to a new center.

Risk Factor Analysis in Vascular Access Complications for Hemodialysis Patients

Background: Chronic kidney disease (CKD) and renal failure remain critical global health challenges, with vascular access complications posing significant obstacles in hemodialysis management. Methods: This study investigates the early and late complications associated with vascular access procedures in a cohort of 1334 patients from Timiș County Emergency Clinical Hospital. Patients were categorized into early complications, occurring within 30 days postoperatively, and late complications, developing beyond this period. Demographic data, comorbidities, and lifestyle factors, including age, gender, body mass index (BMI), smoking status, hypertension, diabetes, and cardiovascular disease (CVD), were recorded and analyzed. Early complications included thrombosis, hemorrhage, edema, and non-maturation, while late complications involved thrombosis, aneurysmal dilation, venous hypertension, and infections. Results: Hemorrhage (32.3%) and thrombosis (30.8%) were the most prevalent early complications, influenced significantly by diabetes and hypertension. Non-maturation showed a strong association with diabetes and cardiovascular disease (odds ratio: 1.70). For late complications, thrombosis was most frequent, with hypertensive patients exhibiting increased risk (relative risk: 1.18). BMI was a significant factor in both early and late complications. Risk analysis using odds ratios and relative risks revealed distinct patterns of complication risks based on comorbidities and smoking status. Logistic regression modeling for thrombosis demonstrated moderate predictive accuracy (AUC: 0.64). Conclusions: These findings suggest that clinical interventions, such as stricter perioperative glycemic and blood pressure control, and personalized surgical strategies for patients with high BMI or comorbidities, could significantly reduce the incidence of vascular access complications and improve outcomes in this high-risk population.

Bismuth-infused perivascular wrap facilitates delivery of mesenchymal stem cells and attenuation of neointimal hyperplasia in rat arteriovenous fistulas

BACKGROUND

Mesenchymal stem cells (MSCs) have emerged as novel therapies for supporting arteriovenous fistula (AVF) maturation, and bioresorbable polymeric scaffolds have enabled sustained MSC delivery into maturing AVFs. However, the radiolucency of biopolymeric wraps prevents in vivo monitoring of their integrity and location, hindering long-term preclinical investigations.

METHODS

We infused bismuth nanoparticles (BiNPs) into polycaprolactone (PCL) to fabricate an electrospun perivascular wrap capable of MSC delivery and conducive to longitudinal monitoring using conventional imaging. We tested the wraps' effects on the attenuation of markers of neointimal hyperplasia (i.e., endothelial dysfunction, hypoxia, and inflammation), the leading cause of AVF failure, in rats with induced chronic kidney disease (n = 3 per time point) for the following groups: control (no wrap), PCL wrap, PCL with MSCs, PCL-Bi (BiNP-infused wrap), and PCL-Bi with MSCs.

RESULTS

Physicochemical characterization and in vitro biocompatibility tests revealed that BiNP infusion did not alter the wrap's non-cytotoxicity toward vascular cells, hemocompatibility, and capacity for MSC loading but facilitated long-term monitoring via micro-computed tomography. After 8 weeks, all treatment groups demonstrated significant improvement in wall-to-lumen ratio on ultrasonography (P < 0.001), neointima-to-lumen ratio on histomorphometry (P < 0.001), and attenuation of neointimal hypoxia on immunohistochemistry (P < 0.05). Compared to non-MSC wraps, MSC-loaded wraps not only attenuated endothelial dysfunction and neointimal inflammation but also reduced hypoxia and inflammation across all vascular layers.

CONCLUSION

These results demonstrate that MSC delivery through a radiopaque polymeric wrap could enhance AVF patency outcomes through the inhibition of multiple pathways inducing AVF failure.

Controlled Delivery of Rosuvastatin or Rapamycin through Electrospun Bismuth Nanoparticle-Infused Perivascular Wraps Promotes Arteriovenous Fistula Maturation

In the context of arteriovenous fistula (AVF) failure, local delivery enables the release of higher concentrations of drugs that can suppress neointimal hyperplasia (NIH) while reducing systemic adverse effects. However, the radiolucency of polymeric delivery systems hinders long-term in vivo surveillance of safety and efficacy. We hypothesize that using a radiopaque perivascular wrap to deliver anti-NIH drugs could enhance AVF maturation. Through electrospinning, we fabricated multifunctional perivascular polycaprolactone (PCL) wraps loaded with bismuth nanoparticles (BiNPs) for enhanced radiologic visibility and drugs that can attenuate NIH─rosuvastatin (Rosu) and rapamycin (Rapa). The following groups were tested on the AVFs of a total of 24 Sprague-Dawley rats with induced chronic kidney disease: control (i.e., without wrap), PCL-Bi (i.e., wrap with BiNPs), PCL-Bi-Rosu, and PCL-Bi-Rapa. We found that BiNPs significantly improved the wraps' radiopacity without affecting biocompatibility. The drug release profiles of Rosu (hydrophilic drug) and Rapa (hydrophobic drug) differed significantly. Rosu demonstrated a burst release followed by gradual tapering over 8 weeks, while Rapa demonstrated a gradual release similar to that of the hydrophobic BiNPs. In vivo investigations revealed that both drug-loaded wraps can reduce vascular stenosis on ultrasonography and histomorphometry, as well as reduce [18F]Fluorodeoxyglucose uptake on positron emission tomography. Immunohistochemical studies revealed that PCL-Bi-Rosu primarily attenuated endothelial dysfunction and hypoxia in the neointimal layer, while PCL-Bi-Rapa modulated hypoxia, inflammation, and cellular proliferation across the whole outflow vein. In summary, the controlled delivery of drugs with different properties and mechanisms of action against NIH through a multifunctional, radiopaque perivascular wrap can improve imaging and histologic parameters of AVF maturation.

External Support of Autologous Internal Jugular Vein Grafts with FRAME Mesh in a Porcine Carotid Artery Model

BACKGROUND

Autologous vein grafts are widely used for bypass procedures in cardiovascular surgery. However, these grafts are susceptible to failure due to vein graft disease. Our study aimed to evaluate the impact of the latest-generation FRAME external support on vein graft remodeling in a preclinical model.

METHODS

We performed autologous internal jugular vein interposition grafting in porcine carotid arteries for one month. Four grafts were supported with a FRAME mesh, while seven unsupported grafts served as controls. The conduits were examined through flowmetry, angiography, macroscopy, and microscopy.

RESULTS

The one-month patency rate of FRAME-supported grafts was 100% (4/4), whereas that of unsupported controls was 43% (3/7, Log-rank p = 0.071). On explant angiography, FRAME grafts exhibited significantly more areas with no or mild stenosis (9/12) compared to control grafts (3/21, p = 0.0009). Blood flow at explantation was higher in the FRAME grafts (145 ± 51 mL/min) than in the controls (46 ± 85 mL/min, p = 0.066). Area and thickness of neo-intimal hyperplasia (NIH) at proximal anastomoses were similar for the FRAME and the control groups: 5.79 ± 1.38 versus 6.94 ± 1.10 mm2, respectively (p = 0.558) and 480 ± 95 vs. 587 ± 52 μm2/μm, respectively (p = 0.401). However, in the midgraft portions, the NIH area and thickness were significantly lower in the FRAME group than in the control group: 3.73 ± 0.64 vs. 6.27 ± 0.64 mm2, respectively (p = 0.022) and 258 ± 49 vs. 518 ± 36 μm2/μm, respectively (p = 0.0002).

CONCLUSIONS

In our porcine model, the external mesh FRAME improved the patency of vein-to-carotid artery grafts and protected them from stenosis, particularly in the mid regions. The midgraft neo-intimal hyperplasia was two-fold thinner in the meshed grafts than in the controls.

Stenosis to stented: decrease in flow disturbances following stent implantation of a diseased arteriovenous fistula

The arteriovenous fistula (AVF) is commonly faced with stenosis at the juxta-anastomotic (JXA) region of the vein. Implantation of a flexible nitinol stent across the stenosed JXA has led to the retention of functioning AVFs leading to the resulting AVF geometry being distinctly altered, thereby affecting the haemodynamic environment within it. In this study, large eddy simulations of the flow field within a patient-specific AVF geometry before and after stent implantation were conducted to detail the change in flow features. Although the diseased AVF had much lower flow rates, adverse flow features, such as recirculation zones and swirling flow at the anastomosis, and jet flow at the stenosis site were present. Larger velocity fluctuations (leading to higher turbulent kinetic energy) stemming from these flow features were apparent in the diseased AVF compared to the stented AVF. The unsteadiness at the stenosis created large regions of wall shear stress (WSS) fluctuations downstream of the stenosis site that were not as apparent in the stented AVF geometry. The larger pressure drop across the diseased vein, compared to the stented vein, was primarily caused by the constriction at the stenosis, potentially causing the lower flow rate. Furthermore, the WSS fluctuations in the diseased AVF could lead to further disease progression downstream of the stenosis. The change in bulk flow unsteadiness, pressure drop, and WSS behaviour confirms that the haemodynamic environment of the diseased AVF has substantially improved following the flexible stent implantation.

Implanted blood vessel external support device for the treatment of distal hypoperfusion ischemic syndrome in arteriovenous fistulas and high-frame-rate Vector Flow quality assessment

INTRODUCTION

Distal hypoperfusion ischemic syndrome (DHIS) is a complication occurring after arteriovenous fistula (AVF) creation. Different surgical alternatives haves been proposed in case of severe DHIS. Aim of the present paper is to present a new technique for DHIS treatment.

MATERIAL AND METHODS

Between the 1st of January 2021 and the 31st December 2021 all the patients referred to our center for DHIS grade 2-4 were treated with a new surgical technique. It consists of AVF remodeling using an external nitinol support (VasQ®) to reduce the risk of outflow vein enlargement and DHIS recurrence. To better appreciate the hemodynamic effects of the surgery, a new ultrasound technique called high-frame-rate Vector Flow (HiFR-VF) was used.

RESULTS

Seven patients (M:F 1:3; mean age 43 ± 12 years, range 29-65) were included in this study. Central line was never necessary, and technical success was 100% at 12 months. The comparison with historical data demonstrated lower recurrence of symptoms in comparison to simple artery-to-vein redo (p 0.50). The HiFR-VF showed flow with limited turbulent characteristics at the anastomosis site.

DISCUSSION AND CONCLUSION

The new technique proposed demonstrated to be safe and effective for treatment of DHIS, preventing symptoms recurrence. Ultrasound examination and HiFR-VF can be considered a valuable method to evaluate complex flows at the levels of vascular anastomosis.

Arteriovenous fistula creation with VasQTM device: A feasibility study to reveal hemodynamic implications

BACKGROUND

Arteriovenous fistula (AVF) is the preferred vascular access (VA) for hemodialysis, but it is still affected by high non-maturation and early failure rates due to stenosis development. Increasing evidence suggests that the presence of turbulent-like flow may play a key role, therefore, to stabilize the flow in the venous segment, an external support device (VasQTM) has been designed. The aim of this study was to provide preliminary evidence of VasQTM impact on AVF hemodynamics as compared to AVFs created with conventional surgery.

METHODS

In this pilot single-center prospective randomized study six patients were enrolled, three in the VasQ group and three in the control group. Contrast-free magnetic resonance imaging (MRI) scans were acquired at 3 days, 3 months and 1 year after AVF surgery and were used to generate 3D patient-specific models. Computational fluid dynamic (CFD) simulations were performed using pimpleFoam, imposing patient-specific flow waveforms derived from ultrasound (US) examinations at the inlet of the proximal and distal artery, and a traction-free condition at the venous outflow. Morphologic and hemodynamic changes occurring over time were compared between VasQ and control AVFs.

RESULTS

Our MRI protocol provided high-quality images suitable for reliable segmentation and reconstruction of patient-specific 3D models of AVFs at all three timepoints in four out of six patients. The VasQTM device maintained the angle between the artery and the vein almost unchanged over time, with a more stable flow in the AVFs supported by the device. In contrast, one of the AVFs of the control group evolved to an extreme dilatation of the vein and highly disturbed flow, while the other developed a stenosis in the juxta-anastomotic region.

CONCLUSIONS

This study demonstrated the feasibility of characterizing the morphological and hemodynamic changes occurring over time in AVFs created using the VasQTM device and provided preliminary evidence of the potential hemodynamic benefits of its use.

VasQ U.S. pivotal study demonstrates the safety and effectiveness of an external vascular support for arteriovenous fistula creation

OBJECTIVE

Arteriovenous fistula (AVF) creation is a commonly performed vascular operation that reports 6-month functional success rates as low as 50%. Recently, a nitinol external vascular support device, VasQ, has shown potential in studies outside the United States (U.S.) to improve AVF outcomes when implanted at creation. Here, the pivotal study results of this novel technology in treating patients in the U.S. are described.

METHODS

VasQ was implanted in 144 patients at 16 centers across the U.S. who were referred for creation of a new AVF and consented for enrollment in a 2-year, prospective, multicenter, single-arm, open-label study. Brachiocephalic (n = 129) and radiocephalic (n = 15) AVFs were analyzed. The primary endpoint was primary patency at 6 months compared against a performance goal of 55% derived from a systematic literature search. Safety endpoints included device-related events, ischemic steal, infection, aneurysm, and seroma at up to 6 months. Minimum arterial size was 2.0 mm; target veins were required to measure 2.5 to 6 mm. Key exclusion criteria were patients <18 or >80 years, those with known ipsilateral central venous occlusion, target cannulation zone venous depth greater than 8 mm, and New York Heart Association class 3 or 4.

RESULTS

Patients were 61% male, 53% White, 35% African American, and 14% Hispanic. Mean age was 60 years, and median body mass index was 30.4. Of the patients, 69% were diabetic, 66% were on dialysis at the time of creation, and 70% had a prior access surgery. At 6 months, steal was observed in 2.1%, infection in 0.7%, and no aneurysms or seromas were seen. Primary patency at 6 months was 66% (P < .021 vs performance goal). Physiological maturation was achieved in 92.4% of patients. Successful two-needle cannulation for patients that entered the study on dialysis was achieved in 88% of VasQ AVFs at a median of 56 days. Pre-dialysis patients who initiated dialysis during the study achieved two-needle cannulation in 81.6% VasQ AVFs. Interventions were required at a rate of 1.07 per patient year over the entire study period. Two-year cumulative patency was 76.6% (95% confidence interval, 67.9%-83.4%) with no statistical difference between patients requiring interventions and those that did not. No patency differences were observed between brachiocephalic and radiocephalic AVFs.

CONCLUSIONS

The U.S. pivotal study results demonstrated improved AVF outcomes and an excellent safety profile with VasQ use relative to traditional AVFs. Under the conditions of this trial, VasQ shows great promise in expeditiously and efficiently enhancing AVF functional success.

Bioresorbable Mesenchymal Stem Cell-Loaded Electrospun Polymeric Scaffold Inhibits Neointimal Hyperplasia Following Arteriovenous Fistula Formation in a Rat Model of Chronic Kidney Disease

Bioresorbable perivascular scaffolds loaded with antiproliferative agents have been shown to enhance arteriovenous fistula (AVF) maturation by inhibiting neointimal hyperplasia (NIH). These scaffolds, which can mimic the three-dimensional architecture of the vascular extracellular matrix, also have an untapped potential for the local delivery of cell therapies against NIH. Hence, an electrospun perivascular scaffold from polycaprolactone (PCL) to support mesenchymal stem cell (MSC) attachment and gradual elution at the AVF's outflow vein is fabricated. Chronic kidney disease (CKD) in Sprague-Dawley rats is induced by performing 5/6th nephrectomy, then AVFs for scaffold application are created. The following groups of CKD rats are compared: no perivascular scaffold (i.e., control), PCL alone, and PCL+MSC scaffold. PCL and PCL+MSC significantly improve ultrasonographic (i.e., luminal diameter, wall-to-lumen ratio, and flow rate) and histologic (i.e., neointima-to-lumen ratio, neointima-to-media ratio) parameters compared to control, with PCL+MSC demonstrating further improvement in these parameters compared to PCL alone. Moreover, only PCL+MSC significantly reduces 18 F-fluorodeoxyglucose uptake on positron emission tomography. These findings suggest that adding MSCs promotes greater luminal expansion and potentially reduces the inflammatory process underlying NIH. The results demonstrate the utility of mechanical support loaded with MSCs at the outflow vein immediately after AVF formation to support maturation by minimizing NIH.

Achieving high maturation and cannulation rates of radial-cephalic arteriovenous fistulas with VasQ™ device

BACKGROUND

Hemodialysis is the predominant treatment modality for chronic kidney disease, with arteriovenous fistula (AVF) being considered to be the preferred type of long-term vascular access. Implantation of the external anastomotic VasQ™ support device during AVF creation has been suggested to improve the functional outcomes of AVFs. In the current study, we report the clinical outcomes when using the device with radial-cephalic AVF (RCAVF) creation in a large cohort over 3 years.

METHODS

One hundred fifty RCAVFs were created between June 2018 and August 2021 with implantation of VasQ™. Time to maturation, cannulation characteristics, and assisted (AP) and secondary patency (SP) rates were analyzed.

RESULTS

In this predominantly male (68%), median 64 years old cohort, 150 VasQ™ devices were implanted. Physiological maturation was achieved in 142/150 (95%) and was unassisted in 133/150 (89%). Of those, 129 matured within 1 month and four additional AVFs within 165 days. Eight AVFs achieved maturation following percutaneous transluminal angioplasty, and one required surgical patch angioplasty. The median time from creation to first successful cannulation in dialysis patients was 41 days. AP at 6, 12, 18, 24, and 30 months was 89%, 81%, 78%, 73%, and 73%, and SP was 94%, 87%, 86%, 84%, and 84%, respectively.

CONCLUSIONS

Consistent use of the VasQ™ device in RCAVF creation demonstrates excellent AVF maturation and patency rates with very low frequency of assisted maturation and interventions for maintenance. The VasQ™ device appears a suitable aid in increasing the creation of functional RCAVFs.

Nano-embedded medical devices and delivery systems in interventional radiology

Nanomaterials research has significantly accelerated the development of the field of vascular and interventional radiology. The incorporation of nanoparticles with unique and functional properties into medical devices and delivery systems has paved the way for the creation of novel diagnostic and therapeutic procedures for various clinical disorders. In this review, we discuss the advancements in the field of interventional radiology and the role of nanotechnology in maximizing the benefits and mitigating the disadvantages of interventional radiology theranostic procedures. Several nanomaterials have been studied to improve the efficacy of interventional radiology interventions, reduce the complications associated with medical devices, improve the accuracy and efficiency of drug delivery systems, and develop innovative imaging modalities. Here, we summarize the recent progress in the development of medical devices and delivery systems that link nanotechnology in vascular and interventional radiology. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease.

Intimal Hyperplasia and Arteriovenous Fistula Failure: Looking Beyond Size Differences

The development of venous intimal hyperplasia (IH) has been historically associated with failure of arteriovenous fistulas (AVF) used for hemodialysis. This long-standing assumption, based on histological observations, has been recently challenged by clinical studies indicating that the size of the intima by itself is not enough to explain stenosis or AVF maturation failure. Irrespective of this lack of association, IH is present in most native veins and fistulas, is prominent in many cases, and suggests a role in the vein that may not be reflected by its dimensions. Therefore, the contribution of IH to AVF dysfunction remains controversial. Using only clinical data and avoiding extrapolations from animal models, we critically discuss the biological significance of IH in vein remodeling, vascular access function, and the response of the venous wall to repeated trauma in hemodialysis patients. We address questions and pose new ones such as: What are the factors that contribute to IH in pre-access veins and AVFs? Do cellular phenotypes and composition of the intima influence AVF function? Are there protective roles of the venous intima? This review explores these possibilities, with hopes of rekindling a critical discussion about venous IH that goes beyond thickness and AVF outcomes.

Multicenter European real-world utilization of VasQ anastomotic external support device for arteriovenous fistulae

OBJECTIVE

To evaluate the outcomes of arteriovenous fistulae (AVF), created with VasQ external support device under standard clinical practice across three vascular access clinics.

METHODS

This multinational, retrospective study evaluated prospectively collected clinical outcomes of both forearm and upper arm brachiocephalic AVF (BCAVF) created using the VasQ device. Fifty-one AVF patients were pooled from three different vascular access centers in Germany, Italy, and Spain. Postprocedure outcomes were assessed by flow measurement with ultrasound examination in all centers. Primary failure, usability, patency, and intervention rates during the study period were evaluated.

RESULTS

Fifty-one VasQ devices were implanted during 37 forearm (36 radiocephalic and 1 ulnar-basilic AVF) and 14 BCAVF procedures. The study population comprised mostly males (73%) and Caucasians (82%), with a mean age of 62.5 years (range, 38-84 years) and mean body mass index of 29.2. One patient died owing to access-unrelated reasons, and one patient was lost to follow-up without AVF assessment after its creation. From the remaining 49, 3 patients had a follow-up of less than 4 weeks and were excluded from maturation, primary failure, and dialysis initiation analysis (because those factors could not be evaluated yet), leaving 46 patients in this evaluation. Maturation was achieved in 91% of patients. The primary failure rate was 9%. A primary patency rate of 77% was observed at 6, 12, and 18 months. The secondary patency rate was 91% at 6 months, and 85% at 12 months and 18 months. Both primary patency and secondary patency did not differ statistically when comparing forearm AVF with BCAVF (P > .25). Successful cannulation was achieved in 86% of patients (32/37) requiring dialysis with a median time from creation to cannulation of 46 days. Of those patients, the functional patency rate was 94%. Five patients underwent seven interventions to maintain or restore patency or functionality, with an overall rate of 0.248 interventions per patient-year.

CONCLUSIONS

AVFs created with VasQ external support device demonstrated promising patency and functionality outcomes in multicentric real-world setting across the two most commonly used anatomic locations.

Artery to vein configuration of arteriovenous fistula improves hemodynamics to increase maturation and patency

Arteriovenous fistulae (AVF) are the preferred mode of hemodialysis access, but 60% of conventional [vein-to-artery (V-A)] AVF fail to mature, and only 50% remain patent at 1 year. We previously showed improved maturation and patency in a pilot study of the radial artery deviation and reimplantation (RADAR) technique that uses an artery-to-vein (A-V) configuration. Here, we show that RADAR exhibits higher rates of maturation, as well as increased primary and secondary long-term patencies. RADAR is also protective in female patients, where it is associated with decreased reintervention rates and improved secondary patency. RADAR and conventional geometries were compared further in a rat bilateral carotid artery-internal jugular vein fistula model. There was decreased cell proliferation and neointimal hyperplasia in the A-V configuration in male and female animals, but no difference in hypoxia between the A-V and V-A configurations. Similar trends were seen in uremic male rats. The A-V configuration also associated with increased peak systolic velocity and expression of Kruppel-like factor 2 and phosphorylated endothelial nitric oxide synthase, consistent with improved hemodynamics. Computed tomography and ultrasound-informed computational modeling showed different hemodynamics in the A-V and V-A configurations, and improving the hemodynamics in the V-A configuration was protective against neointimal hyperplasia. These findings collectively demonstrate that RADAR is a durable surgical option for patients requiring radial-cephalic AVF for hemodialysis access.

Initial single-center experience with a new external support device for the creation of the forearm native arteriovenous fistula for hemodialysis

OBJECTIVE

To assess and compare the maturation rate of the native radiocephalic arteriovenous fistula (RC-AVF) created with and without a nitinol external support (VasQ™ Laminate Medical Technologies Ltd, Tel Aviv, Israel).

METHODS

Data of all consecutive patients who underwent the creation of native RC-AVFs at our center between October 2018 and January 2020 was prospectively collected and retrospectively analyzed.Selected patients who had a suitable vein and a radial artery with triphasic flow at preoperative duplex ultrasound exam and were selected for the creation of a radiocephalic fistula were included. Exclusion criteria were: malignant tumors, acute renal failure, previous upper limb revascularization, and septic status. Patency and maturation, vein, and artery diameter and blood flow rate were assessed at the following intervals: post-operatively, 24 h post-operatively, 1 month, 3 months, and 6 months post-operatively.

RESULTS

Forty-nine patients (31 males, mean age 65.7 years old) were included. Patients who received VasQ™ devices were 25 (VasQ group), the other 24 formed the control group. All patients underwent radio-cephalic AVF placement (21 on the wrist, 20 on the forearm, 8 on the proximal forearm). There were no perioperative complications and fatalities. At 1, 3, and 6 months, primary patency rates were 96 ± 4%, 96 ± 4%, 91 ± 6% (VasQ group) versus 87 ± 7%, 87 ± 7%, 80 ± 9% (control group, P 0.17), secondary patency rates were 96 ± 4%, 96 ± 4%, 91 ± 6% (VasQ group) versus 95 ± 4%, 90 ± 7%, 90 ± 7% (control group, P 0.79). A significantly larger vein diameter increase postoperatively (P 0.009) and a greater maturation rate (96% vs 74%, p 0.044) were found in the VasQ group compared to the control group.

CONCLUSIONS

The use of the VasQ™ device was associated with higher maturation rates and larger vein diameters postoperatively. The patency rates were slightly higher but not significantly. Further studies are needed to confirm these findings.

Patency and functionality of radiocephalic arteriovenous fistulas with an external support device (VasQ™): Real-world single-center experience

BACKGROUND

The VasQTM device was designed to improve the outcome of arteriovenous fistulae by optimizing the hemodynamics of the flow in the juxta-anastomotic region of the arteriovenous fistulae through tailored external support. The aim of the study was to evaluate the impact of the VasQ on outcome of radiocephalic arteriovenous fistulae in a real-world setting.

METHODS

This was a single-center, retrospective analysis of patients with either fistula creation before or after dialysis initiation with implantation of the VasQ device during creation of end-to-side radiocephalic arteriovenous fistulae between June 2018 and May 2019. The flow rate and vein diameter were evaluated intraoperatively, at discharge within 48 h postprocedure and at a follow-up of 1, 3, 6, 9, and 12 months.

RESULTS

Thirty-three VasQ devices were implanted during 33 radiocephalic arteriovenous fistula procedures. The study population comprised mostly of men, with an average age of 66 years. Mean intraoperative flow was 428 mL/min (range: 130-945). All patients were discharged with patent arteriovenous fistulae and mean fistula flow of 740 mL/min (range: 230-1300 mL/min). The primary patency was 100% and 79% at 3 and 6 months, respectively. Cumulative/secondary patency was 100% and 90% at 3 and 6 months, respectively.

CONCLUSION

Data presented here suggest that the VasQ device has the potential to provide benefit to the functionality of radiocephalic arteriovenous fistulae.

Hemodynamic impact of VASQ device in vascular access creation

BACKGROUND

Native arteriovenous fistula is the preferred vascular access in term of functionality, efficiency and complication rate. Nevertheless, research continues to seek strategies to reduce the risk of neointimal hyperplasia and hemodynamic modification. The aim of the study was to evaluate the impact on hemodynamic of the VasQ device in arteriovenous fistulae creation.

METHODS

The analysis included patients who underwent to fistula creation with or without implantation of the VasQ device between May and September 2019. The hemodynamic parameters were evaluated pre-operatively and at a follow-up of 1, 3, 6 months. The patency and complication rate were evaluated.

RESULTS

Fifteen VasQ devices were implanted during 30 arteriovenous fistula surgery. The baseline patients features were similar between groups (VasQ treated/control). At baseline, preoperative arterial flow was similar; radial artery diameter at surgical site was 3.4 ± 0.8 mm in treated and 2.8 ± 0.5 mm in the control group. The mean arterial flow at 1 month was 480 ± 210 mL/min in treated and 561 ± 27 mL/min in the control group. At 3 months the mean arterial flow in treated was 645 ± 143 mL/min versus 824 ± 211 mL/min (p = 0.02) in the control group; at 6 months the arterial flow was 714 ± 146 mL/min versus 810 ± 194 mL/min (p = 0.05) in control group. The cardiac output flow at 6 months in the treated group was 4458 ± 928 mL/min versus 5599 ± 1355 mL/min (p = 0.05) in the control group. At 6 months the primary patency was 73% and 80% and the secondary patency 80% and 86% in treated compared to the control group, respectively. No VASQ device complications were recorded.

CONCLUSION

The analysis of these data suggested that using VasQ device could be protective against the hemodynamic modification that occur during arteriovenous fistulae creation.

Implanted blood vessel external support device (VasQ™) for creation of hemodialysis arteriovenous fistula: A single-center experience

INTRODUCTION

the external support device VasQ is intended to promote arteriovenous fistula (AVF) maturation by maintaining the optimal anastomotic angle in order to minimize blood flow disturbances around the anastomotic area. The aim of the study is to assess efficacy and safety of the VasQ device both in brachiocephalic and radiocephalic fistulae.

METHODS

a single institution prospective study was conducted with implantation of the VasQ device during AVF creation. Clinical and Doppler ultrasounds evaluations were performed at day-1, 1, 6, and 12 months for assessment of device-related adverse events, AVF maturation and patency. Moreover, volume flow rate and diameter of outflow vein were measured. A total of 16 patients were enrolled. Ten brachiocephalic and 6 radiocephalic AVFs were created with VasQ. Preoperatively cephalic vein diameter was 3.6 ± 0.9 mm.

RESULTS

our population included 13 male and 3 females patients, 9 end stage kidney disease in conservative therapy, 4 dialysis treated patients, and 3 transplanted patients; mean age was 74.0 ± 8.1 years; no severe device-related adverse events were observed. Primary patency at 1, 6, and 12 months was 100%, 87.5%, and 67.7%, respectively, while secondary patency was 100%, 100%, and 78.3%, respectively. Comparing brachiocephalic to radiocephalic AVFs no significant differences in patency rates were seen. Overall maturation rate was 94% (15/16). Mean vein diameter measured with Doppler ultrasound at postoperative day-1 and at 1, 6, and 12 months was 5.0 ± 1.0, 5.9 ± 0.9, 7.2 ± 1.6, and 7.9 ± 1.4 mm, respectively, with a mean flow rate at the brachial artery of 841 ± 176, 1052 ± 224, 1261 ± 490, and 1348 ± 477 ml/min, respectively.

CONCLUSIONS

in our limited experience VasQ was safe, with high maturation and patency rates. Positive results suggest a potential benefit for VasQ in AVF.

Challenges and novel therapies for vascular access in haemodialysis

Advances in standards of care have extended the life expectancy of patients with kidney failure. However, options for chronic vascular access for haemodialysis - an essential part of kidney replacement therapy - have remained unchanged for decades. The high morbidity and mortality associated with current vascular access complications highlights an unmet clinical need for novel techniques in vascular access and is driving innovation in vascular access care. The development of devices, biological approaches and novel access techniques has led to new approaches to controlling fistula geometry and manipulating the underlying cellular and molecular pathways of the vascular endothelium, and influencing fistula maturation and formation through the use of external mechanical methods. Innovations in arteriovenous graft materials range from small modifications to the graft lumen to the creation of completely novel bioengineered grafts. Steps have even been taken to create new devices for the treatment of patients with central vein stenosis. However, these emerging therapies face difficult hurdles, and truly creative approaches to vascular access need resources that include well-designed clinical trials, frequent interaction with regulators, interventionalist education and sufficient funding. In addition, the heterogeneity of patients with kidney failure suggests it is unlikely that a 'one-size-fits-all' approach for effective vascular access will be feasible in the current environment.

Novel Approaches to Arteriovenous Access Creation, Maturation, Suitability, and Durability for Dialysis

Since the arteriovenous fistula (AVF) was first conceived over 50 years ago, the goal to create a vascular conduit with predictable and reproducible maturation and durability continues to elude caregivers. Recently, however, advances in the understanding of vascular biology and new technologies now provides us with some optimism; we are moving toward a viable solution. A quickly maturing, sustainable, and durable arteriovenous access may soon be attainable. This review will discuss these advances. There are novel approaches to AVF creation and devices to enhance maturation, advances in arteriovenous graft material(s), and devices to safely prolong the use of tunneled dialysis catheters. Although hemodialysis (HD) access remains a complex problem, these innovations may lead the way to optimizing the care and the quality of life of those patients who have no choice but to proceed with HD.

Arteriovenous access in hemodialysis: A multidisciplinary perspective for future solutions

In hemodialysis, vascular access is a key issue. The preferred access is an arteriovenous fistula on the non-dominant lower arm. If the natural vessels are insufficient for such access, the insertion of a synthetic vascular graft between artery and vein is an option to construct an arteriovenous shunt for punctures. In emergency situations and especially in elderly with narrow and atherosclerotic vessels, a cuffed double-lumen catheter is placed in a larger vein for chronic use. The latter option constitutes a greater risk for infections while arteriovenous fistula and arteriovenous shunt can fail due to stenosis, thrombosis, or infections. This review will recapitulate the vast and interdisciplinary scenario that characterizes hemodialysis vascular access creation and function, since adequate access management must be based on knowledge of the state of the art and on future perspectives. We also discuss recent developments to improve arteriovenous fistula creation and patency, the blood compatibility of arteriovenous shunt, needs to avoid infections, and potential development of tissue engineering applications in hemodialysis vascular access. The ultimate goal is to spread more knowledge in a critical area of medicine that is importantly affecting medical costs of renal replacement therapies and patients’ quality of life.

Recent Advances in Arteriovenous Access Creation for Hemodialysis: New Horizons in Dialysis Vascular Access

Recent advances in technology show promise in providing greater vascular access options for hemodialysis patients. This review discusses novel methods for creating an anastomosis for arteriovenous (AV) fistulas and new materials for prosthetic AV grafts. Two technologies for endovascular arteriovenous fistula creation, the Ellipsys and WavelinQ endovascular systems, are discussed. When an AV fistula is not possible, an AV graft or devices to augment the AV fistula may be appropriate. New materials that have been developed that show promise as an alternative to the expanded polytetrafluoroethylene graft are discussed. Such potential conduits include bioengineered vessels and both allogenic or xenogenic biologic grafts. Devices designed to optimize blood flow to reduce maturation failure and improve AV fistula outcomes are explored.

An Implanted Blood Vessel Support Device for Arteriovenous Fistulas: A Randomized Controlled Trial

RATIONALE & OBJECTIVE

Reducing turbulent blood flow through dialysis arteriovenous fistulas (AVFs) and radial stretching of their venous wall may attenuate hyperplasia and stenosis and improve AVF outcomes in hemodialysis patients. The goal of this study was to evaluate the safety and efficacy of the VasQ implant, which intervenes on these mechanisms by physically supporting the surgical arteriovenous anastomosis.

STUDY DESIGN

Prospective, randomized, controlled, multicenter study.

SETTINGS & PARTICIPANTS

40 consecutive patients with kidney failure referred for creation of a brachiocephalic fistula in 4 vascular access centers in the United Kingdom and Israel.

INTERVENTIONS

AVF surgical creation with placement of the VasQ implant (treatment) versus AVF placement without the implant (control).

OUTCOMES

Safety assessed as percentage of severe device-related adverse events was the primary outcome. Secondary outcomes were efficacy assessments including: (1) AVF maturation at 3 months, defined as cephalic vein diameter≥5mm and flow≥500mL/min; (2) functional cumulative patency, defined as successful 2-needle cannulation for two-thirds or more of all dialysis runs for 1 month in study participants receiving dialysis; (3) cephalic vein diameter and blood flow; and (4) primary and cumulative patency at 6 months.

RESULTS

No severe device-related adverse events were observed. There was no significant difference in maturation at 3 months or primary patency at 6 months between treatment and control (85% vs 80% and 80% vs 66%). Significantly larger vein luminal diameters were observed in the treatment group versus controls at 3 and 6 months (8.27±2.2 vs 6.69±1.8mm [P=0.03] and 9.6±2.5 vs 7.56±2.7mm [P=0.03]). Functional patency at 6 months was significantly greater in the treatment group (100% vs 56% [P = 0.01]).

LIMITATIONS

Small sample size, limited power for secondary end points.

CONCLUSIONS

No safety signals were detected for the VasQ external support of brachiocephalic AVFs. Higher functional patency and vein luminal diameters were achieved with the device at 3 and 6 months. VasQ may safely intervene on mechanisms associated with the disturbed hemodynamic profile in the juxta-anastomotic region.

FUNDING

Funded by Laminate Medical Technologies Ltd.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT02112669.

Primary External Stenting of an Autogenous Brachial-Basilic Upper Arm Transposition

High-volume shunt flow after arteriovenous fistula (AVF) creation for hemodialysis can cause high-output heart failure. We used the Frame™ (Vascular Graft Solutions Ltd., Tel Aviv, Israel) external support, a stent, to limit vein dilatation and consecutive high-volume shunt in a 62-old female who underwent brachial-basilic upper arm transposition. After maturation, the shunt was used for dialysis and showed a plateauing flow volume 3 months after the operation. This case illustrates the safety and feasibility of this intervention when performed during AVF formation.

Molecular Targets for Improving Arteriovenous Fistula Maturation and Patency

The increasing prevalence of chronic and end-stage renal disease creates an increased need for reliable vascular access, and although arteriovenous fistulae (AVF) are the preferred mode of hemodialysis access, 60% fail to mature and only 50% remain patent at one year. Fistulae mature by diameter expansion and wall thickening; this outward remodeling of the venous wall in the fistula environment relies on a delicate balance of extracellular matrix (ECM) remodeling, inflammation, growth factor secretion, and cell adhesion molecule upregulation in the venous wall. AVF failure occurs via two distinct mechanisms with early failure secondary to lack of outward remodeling, that is insufficient diameter expansion or wall thickening, whereas late failure occurs with excessive wall thickening due to neointimal hyperplasia (NIH) and insufficient diameter expansion in a previously functional fistula. In recent years, the molecular basis of AVF maturation and failure are becoming understood in order to develop potential therapeutic targets to aide maturation and prevent access loss. Erythropoietin-producing hepatocellular carcinoma (Eph) receptors, along with their ligands, ephrins, determine vascular identity and are critical for vascular remodeling in the embryo. Manipulation of Eph receptor signaling in adults, as well as downstream pathways, is a potential treatment strategy to improve the rates of AVF maturation and patency. This review examines our current understanding of molecular changes occurring following fistula creation, factors predictive of fistula success, and potential areas of intervention to decrease AVF failure.

Factors affecting arteriovenous fistula dysfunction: A narrative review

Vascular access dysfunction is one of the most important causes of morbidity and mortality in haemodialysis patients, contributing to up to one third of hospitalisations and accounting for a significant amount of the health care costs of these patients. In the past decades, significant scientific advances in understanding mechanisms of arteriovenous fistula maturation and failure have contributed to an increase in the amount of research into techniques for creation and strategies for arteriovenous fistula dysfunction prevention and treatment, in order to improve patient care and outcomes. The aim of this review is to describe the pathogenesis of vascular access failure and provide a comprehensive analysis of the associated risk factors and causes of vascular access failure, in order to interpret possible future therapeutic approaches. Arteriovenous fistula failure is a multifactorial process resulting from the combination of upstream and downstream events with consequent venous neo-intimal hyperplasia and/or inadequate outward remodelling. Inflammation appears to be central in the biology of arteriovenous fistula dysfunction but important triggers still need to be revealed. Given the significant association of arteriovenous fistula failure and patient's prognosis, it is therefore imperative to further research in this area in order to improve prevention, surveillance and treatment, and ultimately patient care and outcomes.

Intraoperative pneumatic tourniquet use may improve the clinical outcomes of arteriovenous fistula creations

OBJECTIVES

A major pathology affecting the usability of arteriovenous fistulas for hemodialysis is juxta-anastomosis stenosis. Intraoperative pneumatic tourniquet eliminates the use of vascular clamps, reduces vascular trauma, and may then reduce the juxta-anastomosis stenosis. The aim of this study was to compare the outcomes of arteriovenous fistula creations using the tourniquet-assisted approach versus the clamp-assisted approach.

METHODS

This retrospective study analyzed the outcomes of primary arteriovenous fistulas created by the lead author from 2008 to 2017 and met the specified inclusion criteria applied to both groups.

RESULTS

A total of 575 patients were included. Upon comparing the tourniquet group (n = 411) with the clamp group (n = 164): the primary arteriovenous fistula failure rate was significantly lower (2.4% vs 7.3%, p = 0.01); the percentage of arteriovenous fistula used for hemodialysis without initial interventions was significantly higher (71.5% vs 45.1%, p < 0.001) and with initial interventions was conversely lower (26.0% vs 47.6%, p < 0.001); the primary patency rate of the whole fistula conduits was significantly higher (44.2% vs 23.0% at 1 year, p < 0.001) and so was the cumulative patency rate (97.2% vs 92.6% at 1 year, p < 0.001); and the juxta-anastomosis primary patency rate (free of interventions for the juxta-anastomosis region) was higher (71.0% vs 47.8% at 1 year, p < 0.001). Based on multivariate Cox proportional hazards regression analyses, the effect of tourniquet use on the juxta-anastomosis primary patency remained significant (hazard ratio = 2.24, 95% confidence interval = 1.72-2.93, p < 0.001) when other significant factors (fistula location, gender, and diabetes) were considered.

CONCLUSION

Intraoperative pneumatic tourniquet may significantly improve the clinical outcomes of arteriovenous fistula creations by reducing juxta-anastomosis trauma and subsequent stenosis.

Arteriovenous conduits for hemodialysis: how to better modulate the pathophysiological vascular response to optimize vascular access durability

Vascular access is the lifeline for patients on hemodialysis. Arteriovenous fistulas (AVFs) are the preferred vascular access, but AVF maturation failure remains a significant clinical problem. Currently, there are no effective therapies available to prevent or treat AVF maturation failure. AVF maturation failure frequently results from venous stenosis at the AVF anastomosis, which is secondary to poor outward vascular remodeling and excessive venous intimal hyperplasia that narrows the AVF lumen. Arteriovenous grafts (AVGs) are the next preferred vascular access when an AVF creation is not possible. AVG failure is primarily the result of venous stenosis at the vein-graft anastomosis, which originates from intimal hyperplasia development. Although there has been advancement in our knowledge of the pathophysiology of AVF maturation and AVG failure, this has not translated into effective therapies for these two important clinical problems. Further work will be required to dissect out the mechanisms of AVF maturation failure and AVG failure to develop more specific therapies. This review highlights the major recent advancements in AVF and AVG biology, reviews major clinical trials, and discusses new areas for future research.

Does blood flow restriction training increase the diameter of forearm vessels in chronic kidney disease patients? A randomized clinical trial

INTRODUCTION:

Blood flow restriction training can be used as an alternative to conventional exercise in chronic kidney disease patients with indication of arteriovenous fistula.

OBJECTIVE:

Evaluating the efficacy of blood flow restriction training in the diameter and distensibility change of the cephalic vein and the diameter and flow of the radial artery, muscle strength and forearm circumference in chronic kidney disease patients with arteriovenous fistula pre-creation.

METHODS:

A blind randomized clinical trial consisting of 26 chronic kidney disease patients allocated into a blood flow restriction training group (blood flow restriction; n = 12) and a group without blood flow restriction training (control group; n = 14). Blood flow restriction was performed at 50% of systolic blood pressure and using 40% of handgrip strength as load for the isometric exercises in both groups.

RESULTS:

An increase in the diameter of the cephalic vein in the 2 cm (p = 0.008) and 10 cm segments (p = 0.001) was observed in the control group. The diameter of the radial artery increased in all segments in the blood flow restriction group (2, 10 and 20 cm; p = 0.005, p = 0.021 and p = 0.018, respectively) and in the 10 and 20 cm segments (p = 0.017 and p = 0.026) in the control group. Handgrip strength only increased in the control group (p = 0.003).

CONCLUSION:

Physical training associated with blood flow restriction increased cephalic vein diameters in both groups and was effective in increasing the diameter of the radial artery; however, it did not demonstrate superiority over the exercise group protocol without blood flow restriction.

Biomaterial-Based Approaches to Address Vein Graft and Hemodialysis Access Failures

Veins used as grafts in heart bypass or as access points in hemodialysis exhibit high failure rates, thereby causing significant morbidity and mortality for patients. Interventional or revisional surgeries required to correct these failures have been met with limited success and exorbitant costs, particularly for the US Centers for Medicare & Medicaid Services. Vein stenosis or occlusion leading to failure is primarily the result of neointimal hyperplasia. Systemic therapies have achieved little long-term success, indicating the need for more localized, sustained, biomaterial-based solutions. Numerous studies have demonstrated the ability of external stents to reduce neointimal hyperplasia. However, successful results from animal models have failed to translate to the clinic thus far, and no external stent is currently approved for use in the US to prevent vein graft or hemodialysis access failures. This review discusses current progress in the field, design considerations, and future perspectives for biomaterial-based external stents. More comparative studies iteratively modulating biomaterial and biomaterial-drug approaches are critical in addressing mechanistic knowledge gaps associated with external stent application to the arteriovenous environment. Addressing these gaps will ultimately lead to more viable solutions that prevent vein graft and hemodialysis access failures.

Future research directions to improve fistula maturation and reduce access failure

With the increasing prevalence of end-stage renal disease, there is a growing need for hemodialysis. Arteriovenous fistulae (AVF) are the preferred type of vascular access for hemodialysis, but maturation and failure continue to present significant barriers to successful fistula use. AVF maturation integrates outward remodeling with vessel wall thickening in response to drastic hemodynamic changes in the setting of uremia, systemic inflammation, oxidative stress, and pre-existent vascular pathology. AVF can fail due to both failure to mature adequately to support hemodialysis and development of neointimal hyperplasia that narrows the AVF lumen, typically near the fistula anastomosis. Failure due to neointimal hyperplasia involves vascular cell activation and migration and extracellular matrix remodeling with complex interactions of growth factors, adhesion molecules, inflammatory mediators, and chemokines, all of which result in maladaptive remodeling. Different strategies have been proposed to prevent and treat AVF failure based on current understanding of the modes and pathology of access failure; these approaches range from appropriate patient selection and use of alternative surgical strategies for fistula creation, to the use of novel interventional techniques or drugs to treat failing fistulae. Effective treatments to prevent or treat AVF failure require a multidisciplinary approach involving nephrologists, vascular surgeons, and interventional radiologists, careful patient selection, and the use of tailored systemic or localized interventions to improve patient-specific outcomes. This review provides contemporary information on the underlying mechanisms of AVF maturation and failure and discusses the broad spectrum of options that can be tailored for specific therapy.