Medial fibrosis, vascular calcification, intimal hyperplasia, and arteriovenous fistula maturation

Cathepsin G promotes arteriovenous fistula maturation by positively regulating the MMP2/MMP9 pathway

BACKGROUND

Arteriovenous fistula (AVF) is currently the preferred vascular access for hemodialysis patients. However, the low maturation rate of AVF severely affects its use in patients. A more comprehensive understanding and study of the mechanisms of AVF maturation is urgently needed.

METHODS AND RESULTS

In this study, we downloaded the publicly available datasets (GSE119296 and GSE220796) from the Gene Expression Omnibus (GEO) and merged them for subsequent analysis. We screened 84 differentially expressed genes (DEGs) and performed the functional enrichment analysis. Next, we integrated the results obtained from the degree algorithm provided by the Cytohubba plug-in, Molecular complex detection (MCODE) plug-in, weighted gene correlation network analysis (WGCNA), and Least absolute shrinkage and selection operator (LASSO) logistic regression. This integration allowed us to identify CTSG as a hub gene associated with AVF maturation. Through the literature search and Pearson's correlation analysis, the genes matrix metalloproteinase 2 (MMP2) and MMP9 were identified as potential downstream effectors of CTSG. We then collected three immature clinical AVF vein samples and three mature samples and validated the expression of CTSG using immunohistochemistry (IHC) and double-immunofluorescence staining. The IHC results demonstrated a significant decrease in CTSG expression levels in the immature AVF vein samples compared to the mature samples. The results of double-immunofluorescence staining revealed that CTSG was expressed in both the intima and media of AVF veins. Moreover, the expression of CTSG in vascular smooth muscle cells (VSMCs) was significantly higher in the mature samples compared to the immature samples. The results of Masson's trichrome and collagen I IHC staining demonstrated a higher extent of collagen deposition in the media of immature AVF veins compared to the mature. By constructing an in vitro CTSG overexpression model in VSMCs, we found that CTSG upregulated the expression of MMP2 and MMP9 while downregulating the expression of collagen I and collagen III. Furthermore, CTSG was found to inhibit VSMC migration.

CONCLUSIONS

CTSG may promote AVF maturation by stimulating the secretion of MMP2 and MMP9 from VSMCs and reducing the extent of medial fibrosis in AVF veins by inhibiting the secretion of collagen I and collagen III.

Redefining vascular repair: revealing cellular responses on PEUU-gelatin electrospun vascular grafts for endothelialization and immune responses on in vitro models

Tissue-engineered vascular grafts (TEVGs) poised for regenerative applications are central to effective vascular repair, with their efficacy being significantly influenced by scaffold architecture and the strategic distribution of bioactive molecules either embedded within the scaffold or elicited from responsive tissues. Despite substantial advancements over recent decades, a thorough understanding of the critical cellular dynamics for clinical success remains to be fully elucidated. Graft failure, often ascribed to thrombogenesis, intimal hyperplasia, or calcification, is predominantly linked to improperly modulated inflammatory reactions. The orchestrated behavior of repopulating cells is crucial for both initial endothelialization and the subsequent differentiation of vascular wall stem cells into functional phenotypes. This necessitates the TEVG to provide an optimal milieu wherein immune cells can promote early angiogenesis and cell recruitment, all while averting persistent inflammation. In this study, we present an innovative TEVG designed to enhance cellular responses by integrating a physicochemical gradient through a multilayered structure utilizing synthetic (poly (ester urethane urea), PEUU) and natural polymers (Gelatin B), thereby modulating inflammatory reactions. The luminal surface is functionalized with a four-arm polyethylene glycol (P4A) to mitigate thrombogenesis, while the incorporation of adhesive peptides (RGD/SV) fosters the adhesion and maturation of functional endothelial cells. The resultant multilayered TEVG, with a diameter of 3.0 cm and a length of 11 cm, exhibits differential porosity along its layers and mechanical properties commensurate with those of native porcine carotid arteries. Analyses indicate high biocompatibility and low thrombogenicity while enabling luminal endothelialization and functional phenotypic behavior, thus limiting inflammation in in-vitro models. The vascular wall demonstrated low immunogenicity with an initial acute inflammatory phase, transitioning towards a pro-regenerative M2 macrophage-predominant phase. These findings underscore the potential of the designed TEVG in inducing favorable immunomodulatory and pro-regenerative environments, thus holding promise for future clinical applications in vascular tissue engineering.

Slowly moving the needle away from Fistula First

OBJECTIVE

In 2019, the management of end-stage kidney disease (ESKD) shifted away from "Fistula First" (FF) to "ESKD Life-Plan: Patient Life-Plan First then Access Needs." Indeed, some patients exhibit such excessive comorbidity that even relatively minor vascular surgery may be complicated. The purpose of this study was to retrospectively assess complications and mortality (and delineate operative futility) in patients undergoing arteriovenous fistula (AVF) creation in the FF era.

METHODS

Consecutive AVFs created in a single institution before 2021 were retrospectively reviewed. Operative futility was defined as never-accessed fistula, no initiation of dialysis, failure of access maturation (despite secondary intervention), hemodialysis access-induced distal ischemia requiring ligation, early loss of secondary patency, and/or patient mortality within the first 6 postoperative months.

RESULTS

A total of 401 AVFs were created including radial-cephalic (44%), brachial-cephalic (41%), and brachial-basilic (15%) constructions. Patients exhibited a mean age of 69 ± 15 years; 63% were male, and most (74%) were already being hemodialyzed at the time of fistula creation. Forty-five patients (11%) suffered a cardiac event, and five patients died (1%) within 90 days of their access surgery. Perioperative cardiac events were significantly more common after age 80 (19% vs 8%; P = .004); age >80 years was an independent predictor of major 90-day complications (odds ratio [OR], 1.88; 95% confidence interval [CI], 1.04-3.39; P = .036) and the sole independent predictor of major morbidity defined as cardiopulmonary complications, stroke, or death within the first year (OR, 2.01; 95% CI, 1.24-3.25; P = .004). Operative futility was encountered in 52% of the cohort (n = 208 patients): 40% (n = 160) of primary AVFs failed to mature despite assistance, 19% (n = 77) had lost secondary patency by 6 months, 13% of patients (n = 53) were never started on dialysis after access creation, 4% (n = 16) were dead by 6 months, 2% of AVFs (n = 10) matured but were never accessed, and 2% (n = 9) required ligation for hemodialysis access-induced distal ischemia. Not surprisingly, the sole independent protector against operative futility was that catheter-based dialysis had been established prior to AVF creation (OR, 0.36; 95% CI, 0.22-0.59; P < .01).

CONCLUSIONS

Approximately 50% of primary AVF operations performed in the aggressive FF era were deemed futile. Octogenarians were particularly prone to futility and complications during this era. A paradigm shift, from FF to an "ESKD Life-Plan" will, hopefully, more thoughtfully match vascular access strategies to individual patient needs.

Small Arteriovenous Anastomosis in Fistula Creation: Establishing a Functional Vascular Access while Minimizing Steal Syndrome

BACKGROUND

The size selection of the arteriovenous (AV) anastomosis in dialysis access creation requires a careful balance: the diameter must be large enough to accommodate sufficient flow for hemodialysis but small enough to minimize the complication of steal syndrome. Steal syndrome affects up to 10% of patients after creation of dialysis access with sometimes devastating consequences. Conventional teaching recommends a 7-10 mm anastomosis. We sought to assess the efficacy of using a smaller (5-6 mm) anastomosis in new arteriovenous fistula (AVF) creation.

METHODS

We conducted a comparative retrospective analysis of patients who underwent fistula creation with a small versus regular size anastomosis at any upper extremity anatomic site between March 2019 and October 2020 at our institution. Anatomic sites included radiocephalic, brachiocephalic, and brachiobasilic. All AV anastomoses were measured intraoperatively to be 5-6 mm in diameter for the small size groups and 8-10 mm for the regular size group. Endpoints included steal syndrome, functional patency, primary patency, and secondary patency.

RESULTS

Out of 110 patients who underwent an AVF creation, 59.1% received a 5-6 mm anastomosis with a median follow-up time of 10 ± 6 months. Patients' demographics and comorbidities were relatively similar between the 2 groups except for a higher rate of hyperlipidemia (55.4% vs. 28.9%, P = 0.008) in the small size group. Patients in the small size group were more likely to undergo a radiocephalic fistula (40% vs. 4.5%, P < 0.001) and to have a smaller mean vein diameter on preoperative duplex ultrasound (3.2±1 mm vs. 3.9±1 mm, P = 0.0016) when compared to their regular size counterparts. During follow-up, none of the patients in the small group developed steal syndrome (0% vs. 9%, P = 0.015). At 1 year, patients in the regular size group achieved higher rates of primary patency (67.9% vs. 46.9%, P = 0.02); however, no difference was seen in 1-year primary-assisted patency (84.9% vs. 73.6%, P = 0.3), secondary patency (89.6% vs. 79.5%, P = 0.3), or functional patency (87.7% vs. 82.2%, P = 0.64) between the small and regular size groups, respectively.

CONCLUSIONS

The use of a 5-6 mm anastomosis in the creation of new AVFs of the upper extremities appears to be a technically safe option for dialysis access. Our experience suggests that smaller anastomosis still creates enough flow to maintain a functional AV access while minimizing the incidence of steal syndrome. Additionally, even with smaller vein sizes preoperative, adequate dialysis access can be created via a small sized anastomosis, including distal arm access. Larger studies with longer follow-up are needed to evaluate long-term outcomes of small anastomosis fistulas.

Luminal pressure gradient and risk of arteriovenous fistula nonmaturation

While arteriovenous fistula (AVF) nonmaturation is a major issue of hemodialysis care, an effective treatment to improve AVF maturation remains lacking. AVF introduces pulsatile arterial blood flow into its venous limb and produces high luminal pressure gradient, which may have adverse effect on vascular remodeling. As such, the aim of the present study is to investigate effect of luminal pressure gradient on AVF nonmaturation. This single-center, prospective observational study includes patients receiving autologous AVF creation. Participants received early postoperative ultrasound 5-7 days after surgery to collect parameters including diameters, flow rates, and volume at inflow and outflow sites. Luminal pressure gradient was estimated by using modified Bernoulli equation. The outcome was spontaneous AVF maturation within 8 weeks after surgery without intervention. Thirty patients were included, of which the mean age was 66.9 years and 70% were male. At the end of study, 13 (43.3%) patients had spontaneous AVF maturation. All demographic and laboratory characteristics were similar between patients with mature and nonmature AVF. Regarding ultrasonographic parameters, nonmature AVF showed significantly higher inflow/outflow diameter ratio, inflow velocity, and luminal pressure gradient. While these 3 parameters were significantly correlated, multivariate logistic regression showed their significant association with AVF nonmaturation. Receiver operating characteristic curve exhibited their high predictive value for AVF nonmaturation. Our findings showed that higher inflow/outflow ratio, inflow velocity, and AVF luminal pressure gradient in early postoperative ultrasound predicted risk of AVF nonmaturation. Reducing inflow/outflow diameter ratio or inflow rate may be an approach to improve AVF maturation. The predictive value of this early assessment might have impact on the clinical practice of AVF care.

Localized Perivascular Therapeutic Approaches to Inhibit Venous Neointimal Hyperplasia in Arteriovenous Fistula Access for Hemodialysis Use

An arteriovenous fistula (AVF) is the preferred vascular access for chronic hemodialysis, but high failure rates restrict its use. Optimizing patients' perioperative status and the surgical technique, among other methods for preventing primary AVF failure, continue to fall short in lowering failure rates in clinical practice. One of the predominant causes of AVF failure is neointimal hyperplasia (NIH), a process that results from the synergistic effects of inflammation, hypoxia, and hemodynamic shear stress on vascular tissue. Although several systemic therapies have aimed at suppressing NIH, none has shown a clear benefit towards this goal. Localized therapeutic approaches may improve rates of AVF maturation by providing direct structural and functional support to the maturating fistula, as well as by delivering higher doses of pharmacologic agents while avoiding the adverse effects associated with systemic administration of therapeutic agents. Novel materials-such as polymeric scaffolds and nanoparticles-have enabled the development of different perivascular therapies, such as supportive mechanical devices, targeted drug delivery, and cell-based therapeutics. In this review, we summarize various perivascular therapeutic approaches, available data on their effectiveness, and the outlook for localized therapies targeting NIH in the setting of AVF for hemodialysis use. Highlights: Most systemic therapies do not improve AVF patency outcomes; therefore, localized therapeutic approaches may be beneficial. Locally delivered drugs and medical devices may improve AVF patency outcomes by providing biological and mechanical support. Cell-based therapies have shown promise in suppressing NIH by delivering a more extensive array of bioactive substances in response to the biochemical changes in the AVF microenvironment.

Early Failure of Arteriovenous Fistula (AVF): The Effect of Diabetes and Hypertension in a Cross-Sectional Study

Background: Identification and control of clinical predictors of arteriovenous (AVF) failure can improve the long-term outcome of hemodialysis patients. The effects of these factors on the outcome of AVF are not still clear. So, we aimed this study to compare the effect of hypertension and diabetes on early failure of AVF. Methods: In this retrospective study, we evaluated 400 patients with ESRD referred to our clinic for the creation of the first AVF from July 14, 2001, through August 7, 2018. One month after AVF creation, the patients were referred to the clinic for patency control. Demographic characteristics, previous history of diabetes and hypertension, and laboratory data of all patients were recorded preoperatively. Data were entered to SPSS v.24 and Study data were analyzed with chi-square and independent student t-test. Then, early failure of AVF and its relationship with a history of diabetes and hypertension were assessed. Results: There was no statistically significant relationship between the history of diabetes and early AVF failure risk in ESRD patients (OR, 0.78; 95% CI, 0.25 to 2.43). Furthermore, the history of hypertension was significantly lower in the early failure of AVF group (OR, -2.82; 95% CI, -1.42 to -5.59). Although, this effect faded when using regression analysis (OR, -2.67; 95% CI, -0.97 to -7.36). There was a higher Body mass index in the non-early failure group (p = 0.041). There was no significant difference in age (p = 0.512), gender (p = 0.091), history of smoking (p = 0.605), treatment with insulin (p = 0.683), oral antidiabetic agents (p = 0.734), duration of diabetes (p = 0.384), and duration of hypertension (p = 0.093). Conclusion: We reported that the history of diabetes was not higher in the early failure group, while there was a lower risk of AVF failure in patients with a previous history of hypertension.

Outcomes of Arteriovenous Fistula Creation in Patients Undergoing Hemodialysis: An Indian Experience

Introduction

Creating an arteriovenous fistula (AVF) to provide a patent and long-term vascular access (VA) for hemodialysis (HD) still remains a challenge. A methodical approach to choosing the appropriate HD access in accordance with patients’ end-stage kidney disease (ESKD) life plan will help them achieve their goals safely. This study summarizes the impact of various factors on the AVF outcomes in an Indian population as well as the necessary considerations before choosing the site of AVF creation.

Materials and methods

This study involved a single-center, retrospective evaluation of all patients who had undergone arteriovenous (AV) access creation for maintenance HD from October 2018 to August 2019 at a center in India.

Results

In our study of 216 cases, the average age at presentation was 43.9 years and the difference in age between the successful and unsuccessful group was not significant. The successful outcomes in males were significantly higher than those in females (p=0.005). The mean venous diameter in the successful group was significantly larger than that in the unsuccessful group. The distal arterial and vein diameter was higher in both males and females of the laborer group compared to the clerical group; however, the outcomes were comparable. The overall complication rate was 22.22%. We had primary patency rates of 83% at the end of one year with a primary failure rate of 8.80%.

Conclusion

Vein diameter was the most important predictive factor for a successful outcome in our study. Factors like age and life expectancy, gender, comorbidities, occupation, and type of anastomosis may not be individually predictive of outcomes but need to be considered before choosing the appropriate site of access creation according to the life plan of the patient. This will reduce morbidity associated with an additional procedure and facilitate the initiation of HD as early as possible. Occupation can be considered as a surrogate for preoperative forearm exercises with the increased caliber of vessels found in people performing heavy/manual labor favoring a more distal AVF creation.

Effect of cilostazol on arteriovenous fistula in hemodialysis patients

BACKGROUND

The maturation and patency of permanent vascular access are critical in patients requiring hemodialysis. Although numerus trials have been attempted to achieve permanently patent vascular access, little have been noticeable. Cilostazol, a phosphodiesterase-3 inhibitor, has been shown to be effective in peripheral arterial disease including vascular injury-induced intimal hyperplasia. We therefore aimed to determine the effect of cilostazol on the patency and maturation of permanent vascular access.

METHODS

This single-center, retrospective study included 194 patients who underwent arteriovenous fistula surgery to compare vascular complications between the cilostazol (n=107) and control (n=87) groups.

RESULTS

The rate of vascular complications was lower in the cilostazol group than in the control group (36.4% vs. 51.7%; p=0.033), including maturation failure (2.8% vs. 11.5%; p=0.016). The rate of reoperation due to vascular injury after hemodialysis initiation following fistula maturation was also significantly lower in the cilostazol group than in the control group (7.5% vs. 28.7%; p<0.001). However, there were no significant differences in the requirement for percutaneous transluminal angioplasty (PTA), rate of PTA, and the interval from arteriovenous fistula surgery to PTA between the cilostazol and control groups.

CONCLUSION

Cilostazol might be beneficial for the maturation of permanent vascular access in patients requiring hemodialysis.

New Frontiers in Vascular Access Practice: From Standardized to Patient-tailored Care and Shared Decision Making

Vascular access planning is critical in the management of patients with advanced kidney disease who elect for hemodialysis for RRT. Policies put in place more than two decades ago attempted to standardize vascular access care around the model of optimal, namely arteriovenous fistula, and least preferred, namely central venous catheter, type of access. This homogenized approach to vascular access care emerged ineffective in the increasingly heterogeneous and complex dialysis population. The most recent vascular access guidelines acknowledge the limitations of standardized care and encourage tailoring vascular access care on the basis of patient and disease characteristics. In this article, we discuss available literature in support of patient-tailored access care on the basis of differences in vascular access outcomes by biologic and social factors-age, sex, and race. Further, we draw attention to the overlooked dimension of patient-reported preferences and shared decision making in the practice of vascular access planning. We discuss milestones to overcome as requisite steps to implement effective shared decision making in vascular access care. Finally, we take into consideration local practice cofactors as major players in vascular access fate. We conclude that a personalized approach to hemodialysis vascular access will require dynamic care specifically relevant to the individual on the basis of biologic factors, fluctuating clinical needs, values, and preferences.

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.

Morphological Lesion Types Are Associated with Primary and Secondary Patency Rates after High-Pressure Balloon Angioplasty for Dysfunctional Arteriovenous Fistulas

BACKGROUND

Neointimal hyperplasia (NIH) is believed to be the main reason for arteriovenous fistula (AVF) dysfunction, but other mechanisms are also recognized to be involved in the pathophysiological process. This study investigated whether different morphological types of AVF lesions are associated with the patency rate after percutaneous transluminal angioplasty (PTA).

METHODS

This retrospective study included 120 patients who underwent PTA for autogenous AVF dysfunction. All the cases were evaluated under Doppler ultrasound (DU) before intervention and divided into 3 types: Type I (NIH type), Type II (non-NIH type), and Type III (mixed type). Prognostic and clinical data were analyzed by Kaplan-Meier analysis and the Cox proportional hazards model.

RESULTS

There was no statistical difference in baseline variables among groups, except for lumen diameter. The primary patency rates in Type I, Type II, and Type III groups were 78.4, 93.2, and 83.2% at 6 months and 59.5, 84.7, and 75.5% at 1 year, respectively. The secondary patency rates in Type I, Type II, and Type III groups were 94.4, 97.1, and 100% at 6 months and 90.5, 97.1, and 94.7% at 1 year, respectively. The Kaplan-Meier curve showed that the primary and secondary patency rates of Type I group were lower than those of Type II group. Multivariable Cox regression analysis demonstrated that postoperative primary patency was correlated with end-to-end anastomosis (hazard ratio [HR] = 2.997, p = 0.008, 95% confidence interval [CI]: 1.328-6.764) and Type I lesion (HR = 5.395, p = 0.004, 95% CI: 1.730-16.824).

CONCLUSIONS

NIH-dominant lesions of AVF evaluated by DU preoperatively were a risk factor for poor primary and secondary patency rate after PTA in hemodialysis patients.

Ultrasound evaluation of access complications: Thrombosis, aneurysms, pseudoaneurysms and infections

Arteriovenous fistula (AVF) complications are classified based on fistula outcomes. This review aims to update colour Doppler (CD) and pulse wave Doppler (PWD) roles in managing early and late complications of the native and prosthetic AVF. Vascular access (VA) failure occurs because inflow or outflow stenosis activates Wirchow's triad inducing thrombosis. Therefore, the diagnosis of the tributary artery and outgoing vein stenosis will be the first topic considered. Post-implantation complications occur from the inability to achieve AVF maturation and dialysis suitability due to inflow/outflow stenosis. Late stenosis is usually a sequence of early defects repaired to maintain patency. Less frequently, in the mature AVF or graft, complications are acquired 'de novo'. They derive either from incorrect management of vascular access (haematoma, pseudoaneurysm, prosthesis infection) or wall pathologies (aneurysm, myxoid valve degeneration, kinking, coiling, abnormal dilation from defects of elastic structures). High-resolution transducers (10-20 MHz) allow the characterization of the wall damage, haemodynamic dysfunctions, early and late complications even if phlebography remains the gold standard for the diagnosis for its sensitivity and specificity.

Effect of cilostazol on arteriovenous fistula in hemodialysis patients

BACKGROUND

The maturation and patency of permanent vascular access are critical in patients requiring hemodialysis. Although numerus trials have been attempted to achieve permanently patent vascular access, little have been noticeable. Cilostazol, a phosphodiesterase-3 inhibitor, has been shown to be effective in peripheral arterial disease including vascular injury-induced intimal hyperplasia. We therefore aimed to determine the effect of cilostazol on the patency and maturation of permanent vascular access.

METHODS

This single-center, retrospective study included 194 patients who underwent arteriovenous fistula surgery to compare vascular complications between the cilostazol (n=107) and control (n=87) groups.

RESULTS

The rate of vascular complications was lower in the cilostazol group than in the control group (36.4% vs. 51.7%; p=0.033), including maturation failure (2.8% vs. 11.5%; p=0.016). The rate of reoperation due to vascular injury after hemodialysis initiation following fistula maturation was also significantly lower in the cilostazol group than in the control group (7.5% vs. 28.7%; p<0.001). However, there were no significant differences in the requirement for percutaneous transluminal angioplasty (PTA), rate of PTA, and the interval from arteriovenous fistula surgery to PTA between the cilostazol and control groups.

CONCLUSION

Cilostazol might be beneficial for the maturation of permanent vascular access in patients requiring hemodialysis.

Arteriovenous fistulas for hemodialysis: Brief review and current problems

The number of people worldwide living with end-stage renal disease is increasing. Arteriovenous fistulas are the preferred method of vascular access in patients who will require hemodialysis. As the number of patients with arteriovenous fistulas grows, the role of physicians who intervene who maintain and salvage these fistulas will grow in importance. This review aims to familiarize practitioners with the rationale for arteriovenous fistula creation, the detection of fistula dysfunction, and the state of the art on fistula maintenance and preservation. Current controversies are briefly reviewed.

Balloon-assisted maturation of autogenous arteriovenous fistulae: A randomized controlled prospective study

BACKGROUND

Current guidelines recommend referral of patient with renal failure for access creation 6 months before planned dialysis. There is a growing cohort of patients that require long-term hemodialysis without adequate preparation. Temporary dialysis catheters and rapid access arteriovenous grafts (AVG) are far from being an ideal solution in this scenario. In an effort to expedite maturation of autogenous arteriovenous fistulae (AVF), balloon-assisted maturation (BAM) was advised by some authors. This technique still lacks the support of high-level evidence studies. We investigated the ability of intra-operative BAM to induce early functional maturation of AVFs.

METHODS

This is a prospective randomized controlled study conducted in a tertiary referral center, with a catchment area of more than 15 million population. Cases were divided into two groups; Group (A), where BAM technique was performed, while in the control group (B), the standard technique was used (NO BAM) for creation of AVFs.

RESULTS

Between June 2017 and May 2019, 300 cases were recruited from a total of 648 primary AVF creation instances. Patients' age ranged from 19 to 89 (mean 51.17 ±SD 15.5) years. Group A (BAM) included 52.3% (n = 157) AVFs, while Group B included 47.7% (n = 143) AVFs. The average maturation time was 3.7 weeks (SD ± 1.3, 95% CI 3.55-3.95) and 5.91 weeks (SD ± 2.2, 95% CI 5.55-6.26) for both groups, respectively (p = 0.0001). 78.3% of the AVFs that underwent BAM showed early maturation within 2-4 weeks vs 32.2% only in the NO BAM group (p = 0.002). Successful functional maturation was higher among cases of the BAM group (93%), compared to the NO BAM group (77%) (p = 0.001). Complication rates were 9.6% and 4.9% in the two groups, respectively (p = 0.042).

CONCLUSION

BAM can play a pivotal role in helping the dialysis society meet the goals of the Fistula First Initiative, keeping in mind that this comes with an increased risk of complications. BAM should be considered only when unplanned early access to long-term dialysis is required.

Reliability of preoperative venous mapping ultrasonography in predicting for autogenous arteriovenous fistula maturation

BACKGROUND

Autogenous arteriovenous fistula creation is the preferred route for vascular access for hemodialysis. Although preoperative venous mapping ultrasonography has been advocated as an operative planning adjunct and recently incorporated into the Society for Vascular Surgery clinical guidelines, controversy remains regarding its usefulness for predicting access success. The purpose of the present retrospective clinical study was to test the hypothesis that vein size measured on routine preoperative venous mapping is a poor predictor of primary fistula maturation.

METHODS

Consecutive upper extremity autogenous arteriovenous fistulas created by three dedicated vascular surgeons were retrospectively reviewed. The demographic characteristics, preoperative venous mapping, functional maturation, and patency were analyzed. The clinically relevant variables were tested for predictive significance using a logistic regression model.

RESULTS

A total of 199 upper extremity autogenous arteriovenous fistulas had been created during a 5-year period. Patients were aged 70 ± 16 years (range, 20-96 years), and 62% were men. Most had already been undergoing dialysis before fistula creation (83%), usually via a tunneled central venous catheter (62%). Radial-cephalic, brachial-cephalic, and brachial-basilic arteriovenous fistulas had been created in 82 patients (41%), 76 patients (38%), and 10 patients (5%), respectively. Fistula maturation, defined as a palpable thrill and/or successful cannulation of the fistula with the ability to deliver a flow rate of 400 mL/min, was achieved in 67% of the patients. A higher body mass index was associated with nonmaturation on both univariate and multivariate analyses (success, 28.6 ± 7.7 kg/m²; vs failed, 31.6 ± 9.4 kg/m²; P = .029; odds ratio [OR], 1.06; 95% confidence interval [CI], 1.02-1.10; P < .01). On univariate analysis, the maximum target vein diameter assessed by preoperative venous mapping was slightly larger in the group achieving successful maturation (2.9 ± 1.1 mm vs 2.6 ± 0.9 mm; P = .014). However, neither the maximum target vein diameter nor a target vein size >3 mm was significantly predictive of maturation on multivariate analysis (maximum vein diameter: OR, 0.65; 95% CI, 0.35-1.22; P = .176; vein size >3 mm: OR, 0.91; 95% CI, 0.32-2.60; P = .857). After a median follow-up of 15 months (interquartile range, 26 months), the primary functional patency, primary-assisted patency, and secondary patency rates were 39.1% ± 0.6%, 94.5% ± 0.6%, and 97.9% ± 0.5%. No association of vein diameter with long-term patency was found.

CONCLUSIONS

Despite the national fistula-first initiatives, most patients still undergo access via catheter at the initiation of hemodialysis. The use of routine preoperative venous mapping does not predict successful primary maturation. Also, no clinically useful predictor of fistula maturation was identified in the present study.

Pre-operative Patient Specific Flow Predictions to Improve Haemodialysis Arteriovenous Fistula Maturation (Shunt Simulation Study): A Randomised Controlled Trial

OBJECTIVE

An arteriovenous fistula (AVF) needs to mature before it becomes suitable to cannulate for haemodialysis treatment. Maturation importantly depends on the post-operative flow increase. Unfortunately, 20-40% of AVFs fail to mature (FTM). A patient specific computational model that predicts immediate post-operative flow was developed, and it was hypothesised that providing information from this model for planning of fistula creation might reduce FTM rates.

METHODS

A multicentre, randomised controlled trial in nine Dutch hospitals was conducted in which patients with renal failure who were referred for AVF creation, were recruited. Patients were randomly assigned (1:1) to the control or computer simulation group. Both groups underwent a work up, with physical and duplex ultrasonography (DUS) examination. In the simulation group the data from the DUS examination were used for model simulations, and based on the immediate post-operative flow prediction, the ideal AVF configuration was recommended. The primary endpoint was AVF maturation defined as an AVF flow ≥500 mL/min and a vein inner diameter of ≥4 mm six weeks post-operatively. The secondary endpoint was model performance (i.e. comparisons between measured and predicted flows, and (multivariable) regression analysis for maturation probability with accompanying area under the receiver operator characteristic curve [AUC]).

RESULTS

A total of 236 patients were randomly assigned (116 in the control and 120 in the simulation group), of whom 205 (100 and 105 respectively) were analysed for the primary endpoint. There was no difference in FTM rates between the groups (29% and 32% respectively). Immediate post-operative flow prediction had an OR of 1.15 (1.06-1.26; p < .001) per 100 mL/min for maturation, and the accompanying AUC was 0.67 (0.59-0.75).

CONCLUSION

Providing pre-operative patient specific flow simulations during surgical planning does not result in improved maturation rates. Further study is needed to improve the predictive power of these simulations in order to render the computational model an adjunct to surgical planning.

Paclitaxel drug-coated balloon angioplasty for the treatment of failing arteriovenous fistulas: a single-center experience

Objectives: To report our experience of angioplasty with Lutonix (Bard Peripheral Vascular, Inc., Tempe, AZ) drug-coated balloon (DCB) for the treatment of failing arteriovenous fistulas (AVF).Materials and methods: Retrospective, single-center analysis consisting of 14 patients treated with Lutonix paclitaxel DCBs in the period from July 2015 through April 2017. We analyzed technical success, clinical success, primary patency of the target lesion, primary patency of the dialysis circuit, and the rate of complications. Regular follow-up of AVF patency was realized by clinical examination and duplex ultrasonography. The Kaplan-Meier survival method was applied to determine the cumulative primary patency of the target lesion and the dialysis circuit.Results: Technical success was 100% and clinical success 92.9%. There were no major or minor complications. Cumulative target lesion primary patency after DCB was 69.2% at 6 months and 31.6% at 12 months. Cumulative vascular circuit primary patency was 61.5% at 6 months and 31.6% at 12 months.Conclusion: Compared to results reported in literature with plain old balloon angioplasty (POBA), Lutonix paclitaxel DCB angioplasty proved a short-term patency benefit in treatment of dialysis AVF stenosis.

Lactic acid-mediated endothelial to mesenchymal transition through TGF-β1 contributes to in-stent stenosis in poly-L-lactic acid stent

Currently, bioresorbable stents made with biodegradable materials are attracting more and more attentions in cardiovascular tissue engineering. Especially, poly-L-lactic acid (PLLA) stent has been regarded as the most promising one due to excellent biodegradability until serious in-stent restenosis at late stage was reported. This imply that the PLLA stent has side effect in cell function, and it is rarely reported the effect of degradation product of PLLA on endothelial function. Here we reported that lactic acid (LA) not acidic pH induced endothelial-to-mesenchymal transition (EndMT) leading to vascular fibrosis which may contribute to in-stent stenosis after PLLA stent implantation. Furthermore, we found TGF-β1 signaling was involved in boosting EndMT by LA. These results demonstrate a mechanism of in-stent stenosis induced by PLLA and indicate its utility for the future design of polymeric vascular scaffolds.

Prediction model for successful radiocephalic arteriovenous fistula creation in patients with diabetic nephropathy

Arteriovenous fistula (AVF) is the most appropriate vascular access for all chronic kidney disease patients for hemodialysis. However, patients with diabetic nephropathy are at increased risk for primary failure after AVF creation, mainly due to atherosclerosis and calcification of blood vessels. We conducted this study to find out the risk factors for primary failure of radiocephalic AVF in end-stage renal disease (ESRD) patients due to diabetic nephropathy and develop a risk predicting model. This study was conducted at a tertiary care teaching hospital of South India. Patients with ESRD due to diabetic nephropathy whom underwent left radiocephalic AVF at wrist were enrolled. Risk factors for primary failure were analyzed by univariate and multivariate logistic regression models. Sixty-six patients were included in the study. Thirty-one patients had a primary failure. Independent risk factors for primary failure were palpable vessel wall of the radial artery (P = 0.003, odds ratio [OR] = 15.317), smaller radial artery diameter (P = 0.001, OR = 16.526), radial artery peak systolic velocity (PSV) <45 cm/s (P = 0.005, OR = 8.494), and linear radial artery calcification (P = 0.006, OR = 7.942). The risk predicting model obtained by adding the score given for each risk factors (vessel wall not palpable = 0, palpable = 1, no linear calcification in digital X-ray = 0, linear calcification = 1, PSV ≥45 cm/s = 0, <45 cm/s = 1 and 2.5 - radial artery diameter in mm) had an area under receiver-operating characteristic curve of 0.886. Cutoff score of 1.5 had sensitivity of 83.9% and specificity of 80.0% for primary failure. Risk predicting model for primary failure based on condition of the vessel wall on palpation, radial artery diameter, flow velocity, and calcification may be helpful for suitable patient selection.

Transcriptomics of Human Arteriovenous Fistula Failure: Genes Associated With Nonmaturation

RATIONALE & OBJECTIVE

Improving arteriovenous fistula (AVF) outcomes requires better understanding of the biology underlying maturation or failure. Our current knowledge of maturation relies on extrapolation from other vascular pathologies, which does not incorporate unique aspects of AVF remodeling. This study compares the RNA expression of pre-access (native) veins and AVFs with distinct maturation outcomes.

STUDY DESIGN

Case-control study.

SETTING & PARTICIPANTS

64 patients undergoing 2-stage AVF surgeries at a single center. 19 native veins and 19 AVF samples were analyzed using RNA sequencing (RNA-seq). 58 native veins were studied using real-time polymerase chain reaction; 45, using immunohistochemistry; and 19, using Western blot analysis.

PREDICTOR

RNA expression in native veins and AVFs.

OUTCOME

Anatomic nonmaturation, defined as an AVF that never achieved an internal diameter ≥ 6mm.

ANALYTICAL APPROACH

Pre-access native veins and AVF samples were obtained from patients undergoing 2-stage AVF creation. Veins that subsequently matured or failed after access creation were analyzed using RNA-seq to search for genes associated with maturation failure. Genes associated with nonmaturation were confirmed using real-time polymerase chain reaction, immunohistochemistry, and Western blot analysis. In addition, the association between pre-access gene expression and postoperative morphology was evaluated. RNA-seq was also performed on AVFs to search for transcriptional differences between AVFs that matured and those that failed at the time of transposition.

RESULTS

Pro-inflammatory genes (CSF3R, FPR1, S100A8, S100A9, and VNN2) were upregulated in pre-access veins that failed (false discovery rate < 0.05), and their expression colocalized to smooth muscle cells. Expression of S100A8 and S100A9 correlated with postoperative intimal hyperplasia and the product of medial fibrosis and intimal hyperplasia (r=0.32-0.38; P < 0.05). AVFs that matured or failed were transcriptionally similar at the time of transposition.

LIMITATIONS

Small sample size, analysis of only upper-arm veins and transposed fistulas.

CONCLUSIONS

Increased expression of proinflammatory genes in pre-access veins appears to be associated with greater risk for AVF nonmaturation.

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.

Vascular Access for Hemodialysis Patients: New Data Should Guide Decision Making

This commentary critically examines key assumptions and recommendations in the 2006 Kidney Disease Outcomes Quality Initiative vascular access guidelines, and argues that several are not relevant to the contemporary United States hemodialysis population. First, the guidelines prefer arteriovenous fistulas (AVFs) over arteriovenous grafts (AVGs), on the basis of their superior secondary survival and lower frequency of interventions and infections. However, intent-to-treat analyses that incorporate the higher primary failure of AVFs, demonstrate equivalent secondary survival of both access types. Moreover, the lower rate of AVF versus AVG infections is counterbalanced by the higher rate of catheter-related bloodstream infections before AVF maturation. In addition, AVFs with assisted maturation (interventions before successful AVF use), which account for about 50% of new AVFs, are associated with inferior secondary patency compared with AVGs without intervention before successful use. Second, the guidelines posit lower access management costs for AVFs than AVGs. However, in patients who undergo AVF or AVG placement after starting dialysis with a central venous catheter (CVC), the overall cost of access management is actually higher in patients receiving an AVF. Third, the guidelines prefer forearm over upper arm AVFs. However, published data demonstrate superior maturation of upper arm versus forearm AVFs, likely explaining the progressive increase in upper arm AVFs in the United States. Fourth, AVFs are thought to fail primarily because of aggressive juxta-anastomotic stenosis. However, recent evidence suggests that many AVFs mature despite neointimal hyperplasia, and that suboptimal arterial vasodilation may be an equally important contributor to AVF nonmaturation. Finally, CVC use is believed to result in excess mortality in patients on hemodialysis. However, recent data suggest that CVC use is simply a surrogate marker of sicker patients who are more likely to die, rather than being a mediator of mortality.

Abnormalities of vascular histology and collagen fiber configuration in patients with advanced chronic kidney disease

INTRODUCTION:

Several histologic features have been identified in the upper-extremity arteries and veins of patients with advanced chronic kidney disease, which may affect arteriovenous fistula maturation. However, it is unclear whether these chronic kidney disease vascular features are abnormal.

METHODS:

We obtained upper-extremity arterial and venous specimens from 125 advanced chronic kidney disease patients undergoing arteriovenous fistula creation and from 15 control subjects. We quantified medial fibrosis, micro-calcification, and intimal hyperplasia with appropriate histology stains. We characterized medial collagen fiber configuration in second-harmonic-generation microscopy images for the fiber anisotropy index and the dominant fiber direction.

RESULTS:

The advanced chronic kidney disease patients were significantly younger than control subjects (53 ± 14 years vs 76 ± 11 years, p < 0.001). After controlling for age, the chronic kidney disease patients had greater arterial medial fibrosis (69% ± 14% vs 51% ± 10%, p < 0.001) and greater arterial micro-calcification (3.03% ± 5.17% vs 0.01% ± 0.03%, p = 0.02), but less arterial intimal thickness (30 ± 25 µm vs 63 ± 25 µm, p < 0.001), as compared to control subjects. The anisotropy index of medial collagen fibers was lower in both arteries (0.24 ± 0.10 vs 0.44 ± 0.04, p < 0.001) and veins (0.28 ± 0.09 vs 0.53 ± 0.10, p < 0.001) in chronic kidney disease patients, indicating that orientation of the fibers was more disordered. The dominant direction of medial collagen fibers in chronic kidney disease patients was greater in the arteries (49.3° ± 23.6° vs 4.0° ± 2.0°, p < 0.001) and the veins (30.0° ± 19.6° vs 3.9° ± 2.1°, p < 0.001), indicating that the fibers in general were aligned more perpendicular to the lumen.

CONCLUSION:

Advanced chronic kidney disease is associated with several abnormalities in vascular histology and collagen fiber configuration. Future research is needed to investigate whether these abnormalities affect the maturation outcomes of arteriovenous fistulas.

Microcalcification in the arterial wall and its relationship to the ultrasound criteria of maturation of the arteriovenous fistula

INTRODUCTION:

A functioning and reliable arteriovenous fistula is a lifeline for individuals suffering from chronic kidney disease. The success and failure to arteriovenous fistula maturation have been frequently related to patient and surgeon factors.

METHOD:

In total, 138 participants with stage IV and V chronic kidney disease were included in this prospective observational study. Preoperative vascular mapping using ultrasound was performed to evaluate the condition and size of the vessels to fulfil the inclusion criteria. Intraoperatively, the vessel size was measured prior to anastomosis under magnified view. A specimen from the arterial wall of 5 mm in diameter was obtained from the arterotomy for histopathology assessment. Arteriovenous maturation was assessed at 6 weeks with the guidance of the ultrasound criteria of rule of sixes.

RESULTS:

From the total of 138 participants, 110 participants (79.7%) had matured arteriovenous fistula in 6 weeks. The mean size of the artery measured intraoperatively was 3.82 ± 1.33 mm and the vein was 4.05 ± 1.20 mm. Microcalcification in the arterial media which was hypothesised to be the cause of the arteriovenous fistula failure was insignificant, with a p value of 0.115. Despite having atherosclerosis in the artery, 83.3% of the arteriovenous fistula matured.

CONCLUSION:

Microcalcification and atherosclerosis are frequently seen in the arteries of chronic kidney disease patients, but they do not explain arteriovenous fistula non-maturation.

Association of Preexisting Arterial Intimal Hyperplasia with Arteriovenous Fistula Outcomes

BACKGROUND AND OBJECTIVES

Preoperative arterial function is associated with arteriovenous fistula (AVF) development. Because arterial pathology may correlate with its function, preexisting arterial intimal hyperplasia may be associated with AVF development.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Vascular specimens obtained from 125 patients (with minimal 2 mm arterial diameter and 2.5 mm venous diameter) undergoing AVF creation were quantified for arterial intimal hyperplasia, arterial medial fibrosis, arterial microcalcification, and venous intimal hyperplasia. A 6-week postoperative ultrasound quantified AVF diameter, blood flow, and stenosis. Clinical AVF maturation was assessed using a predefined protocol. In a prospective cohort study design, we investigated the association of preexisting arterial intimal hyperplasia with the postoperative AVF diameter, blood flow, stenosis, and clinical maturation failure, after controlling for baseline demographics, comorbidities, and preoperative vein diameter. Additional analyses evaluated whether other vascular pathologies interacted with arterial intimal hyperplasia in affecting AVF outcomes.

RESULTS

The median intimal thickness of the native artery was 22.0 μm (interquartile range, 14.8-37.1 μm). The median postoperative AVF diameter was 4.8 (interquartile range, 3.7-6.8) mm, blood flow was 796 (interquartile range, 413-1036) ml/min, and stenosis was present in 37 out of 98 patients with ultrasound data (38%). AVF nonmaturation occurred in 37 out of 125 patients (30%). Preexisting arterial intimal thickness was not significantly associated with AVF blood flow (-12 ml/min; 95% confidence interval [95% CI], -55 to 30 ml/min), diameter (-0.04 mm; 95% CI, -0.21 to 0.14 mm), stenosis (odds ratio, 0.93; 95% CI, 0.75 to 1.14), or clinical maturation failure (odds ratio, 1.07; 95% CI, 0.90 to 1.28), all per 10 μm increase. There was no significant interaction of preexisting arterial intimal thickness and postoperative AVF outcomes with arterial medial fibrosis, arterial microcalcification, or venous intimal hyperplasia.

CONCLUSIONS

Preexisting arterial intimal hyperplasia is not associated with the 6-week AVF blood flow, diameter or stenosis, or clinical maturation when the preoperative arterial diameter is ≥2 mm.

Fibrotic Venous Remodeling and Nonmaturation of Arteriovenous Fistulas

The frequency of primary failure in arteriovenous fistulas (AVFs) remains unacceptably high. This lack of improvement is due in part to a poor understanding of the pathobiology underlying AVF nonmaturation. This observational study quantified the progression of three vascular features, medial fibrosis, intimal hyperplasia (IH), and collagen fiber organization, during early AVF remodeling and evaluated the associations thereof with AVF nonmaturation. We obtained venous samples from patients undergoing two-stage upper-arm AVF surgeries at a single center, including intraoperative veins at the first-stage access creation surgery and AVFs at the second-stage transposition procedure. Paired venous samples from both stages were used to evaluate change in these vascular features after anastomosis. Anatomic nonmaturation (AVF diameter never ≥6 mm) occurred in 39 of 161 (24%) patients. Neither preexisting fibrosis nor IH predicted AVF outcomes. Postoperative medial fibrosis associated with nonmaturation (odds ratio [OR], 1.55; 95% confidence interval [95% CI], 1.05 to 2.30; P=0.03, per 10% absolute increase in fibrosis), whereas postoperative IH only associated with failure in those individuals with medial fibrosis over the population's median value (OR, 2.63; 95% CI, 1.07 to 6.46; P=0.04, per increase of 1 in the intima/media ratio). Analysis of postoperative medial collagen organization revealed that circumferential alignment of fibers around the lumen associated with AVF nonmaturation (OR, 1.38; 95% CI, 1.03 to 1.84; P=0.03, per 10° increase in angle). This study demonstrates that excessive fibrotic remodeling of the vein after AVF creation is an important risk factor for nonmaturation and that high medial fibrosis determines the stenotic potential of IH.

Reduced Expression of Glutathione S-Transferase 4 Promotes Vascular Neointimal Hyperplasia in CKD

Neointima formation is the leading cause of arteriovenous fistula (AVF) failure. We have shown that CKD accelerates this process by transforming the vascular smooth muscle cells (SMCs) lining the AVF from a contractile to the synthetic phenotype. However, the underlying mechanisms affecting this transformation are not clear. Previous studies have shown that the α-class glutathione transferase isozymes have an important role in regulating 4-hydroxynonenal (4-HNE)-mediated proliferative signaling of cells. Here, using both the loss- and gain-of-function approaches, we investigated the role of glutathione S-transferase α4 (GSTA4) in modulating cellular 4-HNE levels for the transformation and proliferation of SMCs. Compared with non-CKD controls, mice with CKD had downregulated expression of GSTA4 at the mRNA and protein levels, with concomitant increase in 4-HNE in arteries and veins. This effect was associated with upregulated phosphorylation of MAPK signaling pathway proteins in proliferating SMCs. Overexpressing GSTA4 blocked 4-HNE-induced SMC proliferation. Additionally, inhibitors of MAPK signaling inhibited the 4-HNE-induced responses. Compared with wild-type mice, mice lacking GSTA4 exhibited increased CKD-induced neointima formation in AVF. Transient expression of an activated form of GSTA4, achieved using a combined Tet-On/Cre induction system in mice, lowered levels of 4-HNE and reduced the proliferation of SMCs. Together, these results demonstrate the critical role of GSTA4 in blocking CKD-induced neointima formation and AVF failure.

Intimal Hyperplasia, Stenosis, and Arteriovenous Fistula Maturation Failure in the Hemodialysis Fistula Maturation Study

Intimal hyperplasia and stenosis are often cited as causes of arteriovenous fistula maturation failure, but definitive evidence is lacking. We examined the associations among preexisting venous intimal hyperplasia, fistula venous stenosis after creation, and clinical maturation failure. The Hemodialysis Fistula Maturation Study prospectively observed 602 men and women through arteriovenous fistula creation surgery and their postoperative course. A segment of the vein used to create the fistula was collected intraoperatively for histomorphometric examination. On ultrasounds performed 1 day and 2 and 6 weeks after fistula creation, we assessed fistula venous stenosis using pre-specified criteria on the basis of ratios of luminal diameters and peak blood flow velocities at certain locations along the vessel. We determined fistula clinical maturation using criteria for usability during dialysis. Preexisting venous intimal hyperplasia, expressed per 10% increase in a hyperplasia index (range of 0%-100%), modestly associated with lower fistula blood flow rate (relative change, -2.5%; 95% confidence interval [95% CI], -4.6% to -0.4%; P=0.02) at 6 weeks but did not significantly associate with stenosis (odds ratio [OR], 1.07; 95% CI, 1.00 to 1.16; P=0.07) at 6 weeks or failure to mature clinically without procedural assistance (OR, 1.07; 95% CI, 0.99 to 1.15; P=0.07). Fistula venous stenosis at 6 weeks associated with maturation failure (OR, 1.98; 95% CI, 1.25 to 3.12; P=0.004) after controlling for case mix factors, dialysis status, and fistula location. These findings suggest that postoperative fistula venous stenosis associates with fistula maturation failure. Preoperative venous hyperplasia may associate with maturation failure but if so, only modestly.

Pre-existing arterial pathologic changes affecting arteriovenous fistula patency and cardiovascular mortality in hemodialysis patients

The radiocephalic arteriovenous fistula (AVF) provides optimal vascular access for hemodialysis; it has a higher long-term patency rate and fewer complications than other vascular access methods. However, the AVF has a high primary failure rate. The presence of small-diameter vessels at anastomosis sites is an important risk factor for AVF failure. However, in a recent study, despite selecting an adequate artery and vein for creating an AVF by routine preoperative vascular mapping, AVF maturation and primary failure occurred. Thus, pre-existing arteriosclerosis at AVF anastomosis sites likely contributes to AVF failure. In this review, we discuss the relationship between pathologic changes and AVF patency in hemodialysis patients. Because arteriosclerosis of the major arteries such as the coronary and carotid arteries is associated with cardiovascular mortality, we also review the impact of arteriosclerosis of upper arm arteries at AVF anastomosis sites on cardiovascular mortality in hemodialysis patients.

Upper Extremity Medial Arterial Calcification and Peripheral Artery Disease in Asymptomatic Patients With Chronic Kidney Disease in Predialysis Stage

Two types of peripheral artery disease (PAD) in asymptomatic patients with chronic kidney disease (CKD) can be detected by the use of duplex Doppler: medial arterial calcification (MAC) and occlusive PAD. The aim of this pilot study is to evaluate different types of subclinical PAD in upper extremities of patients with CKD. The prevalence of upper extremity MAC and occlusive PAD was investigated in 41 asymptomatic patients with CKD and 18 controls with normal kidney function, using duplex Doppler ultrasound, according to the vascular laboratory protocol. A mild-to-severe MAC was significantly more prevalent in patients with CKD compared to the control group ( P = .015), mostly in radial arteries (RAs; P = .002 and P = .016, respectively). The prevalence of occlusive PAD was not significantly different between the 2 groups ( P = .381). Patients in the CKD group were younger, nonsmokers, and more often had hypertension ( P = .038, P = .038, and P = .034, respectively). A duplex ultrasound screening for upper extremity subclinical PAD in patients with CKD in a predialysis stage may identify patients with mild-to-severe MAC which is important in surgery of hemodialysis access.

The Effect of Arterial Curvature on Blood Flow in Arterio-Venous Fistulae: Realistic Geometries and Pulsatile Flow

Arterio-Venous Fistulae (AVF) are regarded as the "gold standard" method of vascular access for patients with End-Stage Renal Disease (ESRD) who require haemodialysis. However, up to 60% of AVF do not mature, and hence fail, as a result of Intimal Hyperplasia (IH). Unphysiological flow and oxygen transport patterns, associated with the unnatural and often complex geometries of AVF, are believed to be implicated in the development of IH. Previous studies have investigated the effect of arterial curvature on blood flow in AVF using idealized planar AVF configurations and non-pulsatile inflow conditions. The present study takes an important step forwards by extending this work to more realistic non-planar brachiocephalic AVF configurations with pulsatile inflow conditions. Results show that forming an AVF by connecting a vein onto the outer curvature of an arterial bend does not, necessarily, suppress unsteady flow in the artery. This finding is converse to results from a previous more idealized study. However, results also show that forming an AVF by connecting a vein onto the inner curvature of an arterial bend can suppress exposure to regions of low wall shear stress and hypoxia in the artery. This finding is in agreement with results from a previous more idealized study. Finally, results show that forming an AVF by connecting a vein onto the inner curvature of an arterial bend can significantly reduce exposure to high WSS in the vein. The results are important, as they demonstrate that in realistic scenarios arterial curvature can be leveraged to reduce exposure to excessively low/high levels of WSS and regions of hypoxia in AVF. This may in turn reduce rates of IH and hence AVF failure.

Histopathology of Veins Obtained at Hemodialysis Arteriovenous Fistula Creation Surgery

Stenosis from venous neointimal hyperplasia is common in native arteriovenous fistulas (AVFs). However, the preexisting histologic characteristics of veins at fistula creation, and associations thereof with baseline patient factors, have not been well characterized. In this study, we conducted histologic analysis of a segment of the vein used for anastomosis creation, obtained during AVF creation from 554 of the 602 participants in the multicenter Hemodialysis Fistula Maturation Cohort Study. We quantified intimal and medial areas and lengths of the internal and external elastic lamina by morphometry and assessed venous wall cells by immunohistochemistry, extracellular matrix with Movat stain, and calcium deposition by alizarin red stain. We also studied a representative subset of veins for markers of monocyte/macrophage content, cell proliferation, apoptosis, and neoangiogenesis. Neointima occupied >20% of the lumen in 57% of fully circumferential vein samples, and neointimal hyperplasia associated positively with age and inversely with black race. The neointima was usually irregularly thickened, sometimes concentric, and contained α-smooth muscle actin-expressing cells of smooth muscle or myofibroblast origin. Proteoglycans admixed with lesser amounts of collagen constituted the predominant matrix in the neointima. In 82% of vein samples, the media of vessel walls contained large aggregates of collagen. A minority of veins expressed markers of inflammation, cell proliferation, cell death, calcification, or neoangiogenesis. In conclusion, we observed preexisting abnormalities, including neointimal hyperplasia and prominent accumulation of extracellular matrix, in veins used for AVF creation from a substantial proportion of this cohort.

Maintaining Patency of Vascular Access for Haemodialysis

All types of vascular access, a necessity for haemodialysis, are prone to thrombosis and if untreated this results in failure. Thrombosis results from the combination of impaired blood flow, endothelial and vessel wall injury and a propensity towards pro-coagulative states, either intrinsic or aggravated by dialysis or dehydration. The treatment of access thrombosis relies on removal of the clot (thrombectomy) and treatment of the underlying problem. In most cases this is stenosis secondary to neointimal hyperplasia which can occur early (failure to mature) or later. Pharmacological approaches have largely been shown to be ineffective at prevention of thrombosis. The mainstay of preventing access failure may be in surveillance and detecting stenosis prior to occlusion although the optimal protocol to achieve this remains undefined. Management of thrombosed access is via either surgical and radiological approaches. Multiple techniques and devices are available for thrombectomy and the choice is usually based on local expertise and availability rather than evidence as few trials have been performed to allow robust comparisons. This paper outlines the basis of access thrombosis and discusses the currently available techniques for treatment.

Administration of a High-Dose Erythropoietin-Stimulating Agent in Hemodialysis Patients is Associated with Late Arteriovenous Fistula Failure

PURPOSE

Investigating the risk of vascular access failure is critical for maintenance hemodialysis (MHD) patients. Erythropoietin stimulating agents (ESA) typically used for anemia of chronic kidney disease (CKD) may also stimulate neointimal hyperplasia, which is the most important factor in late arteriovenous fistula (AVF) failure. The aim of this study was to investigate whether ESA treatment is associated with late AVF failure.

MATERIALS AND METHODS

The late AVF failure group comprised 51 patients who underwent percutaneous intervention or surgery for fistula revision after successful use for at least three months. There were 51 controls whose AVF had been patent for at least 24 months.

RESULTS

The mean time from the first cannulation to late loss of AVF patency was 8.4±4.2 months. The average weekly dose of ESA was significantly higher in patients with AVF failure (4782.2±2360.5 IU/mL/wk vs. 7161.8±2775.2 IU/mL/wk, p<0.001). The only independent predictor of late AVF failure in multivariate analysis was high average ESA dose (odds ratio=1.015, 95% confidence interval=1.002-1.028, p=0.022).

CONCLUSION

Patients with late AVF patency loss exhibit an association with a higher dose of ESA, although causality is unproven. Further study to elucidate potential mechanisms is warranted.

The Significance of Inflow Artery and Tourniquet Derived Cephalic Vein Diameters on Predicting Successful Use and Patency of Arteriovenous Fistulas for Haemodialysis

OBJECTIVE

To investigate the significance of inflow artery and cephalic vein diameters on predicting patency of radiocephalic and brachiocephalic arteriovenous fistulas (AVFs).

DESIGN

Single centre study with retrospective analysis of prospectively collected data between November 2010 and July 2015.

METHODS

A detailed history and physical examination was undertaken, including age, gender, history and duration of haemodialysis, cause of chronic kidney disease, and the presence of comorbidities/risk factors. Pre-operative arterial and venous upper extremity mapping was performed and inner vessel diameter was recorded, using a tourniquet for the veins. Outcome measures included AVF use (functionality), primary, primary assisted, secondary, and functional secondary patency.

RESULTS

One hundred and thirty five AVFs (57 and 78 radiocephalic and brachiocephalic AVFs, respectively) were constructed and followed up for 5 years. A cephalic vein diameter <4.3 mm (lower three quartiles) was the single independent predictor of inferior secondary and also functional secondary patency of radiocephalic AVFs (p = .02, HR 11.2, 95% CI 1.44-90.9). A brachial artery diameter ≤4.1 mm (lowest quartile) was an independent predictor of AVF functionality (57% vs. 83% for larger arteries, p = .017), and inferior primary, primary assisted, secondary, and functional secondary patency of brachiocephalic AVFs (primary assisted patency 21.9% vs. 55.9% at 3 years, p = .001/log-rank test, HR 3.1, p = .002/Cox regression). The presence of lower extremity PAD or use of dual antithrombotics was also independently associated with an inferior secondary patency. The number of risk factors (brachial artery diameter ≤4.1 mm, PAD, and use of dual antithrombotics) demonstrated risk stratification capabilities for functional secondary patency.

CONCLUSIONS

Among patients undergoing radiocephalic AVFs, a tourniquet derived cephalic vein diameter <4.3 mm was the single independent predictor of inferior secondary and functional secondary patency. Among patients undergoing brachiocephalic AVFs, all patency rates were inferior in the presence of a brachial artery diameter ≤4.1 mm and secondary patency was inferior in the presence of multiple risk factors.

Cilostazol May Improve Maturation Rates and Durability of Vascular Access for Hemodialysis

Cilostazol is effective in controlling pathophysiological pathways similar or identical to those involved in nonmaturation and failure of the arteriovenous access. This case–control study examined whether cilostazol would improve maturation rates and durability of vascular access for hemodialysis. The treatment group included 33 patients who received cilostazol for ≥30 days prior to creation of a dialysis access and continued with cilostazol therapy for ≥60 days after surgery. The matched (gender, age, race, diabetes, and the year of surgery) control group included 116 patients who underwent the same procedure but did not receive cilostazol prior to and at least 3 months after surgery. Primary outcomes were maturation and, for those that matured, time of functioning access, defined as the time from the first use to irreparable failure of the access. Secondary outcomes were time to maturation, complications, and time to first complication. Study group patients were 3.8 times more likely to experience fistula maturation compared to the controls (88% vs 66%, RR = 3.8, 95% confidence interval: 1.3-11.6, P = .016). Fewer patients in the study group had complications (76% vs 92%, P = .025), and the time from construction of the fistula to the first complication was longer (345.6 ± 441 days vs 198.3 ± 185.0 days, P = .025). Time to maturation was similar in both groups (119.3 ± 62.9 days vs 100.2 ± 61.7 days, P = .2). However, once matured, time to failure was significantly longer in the treatment group (903.7 ± 543.6 vs 381.6 ± 317.2 days, P = .001). Multivariate analysis confirmed that the likelihood of maturation was significantly higher in the treatment group patients. These results suggest that dialysis access patients may benefit from preoperative and postoperative cilostazol therapy. If confirmed by a randomized trial, this treatment will have a major beneficial impact on patients dependent on a well-functioning access for their hemodialysis.

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.

Very low protein diets supplemented with keto-analogues in ESRD predialysis patients and its effect on vascular stiffness and AVF Maturation

Background

Native arteriovenous fistula (AVF) is the most appropriate type of vascular access for chronic dialysis. Its patency rates depend on vascular wall characteristics. Ketoacid analogues of essential amino acids (KA/EAA) are prescribed in end-stage renal disease (ESRD) pre-dialysis patients to lower toxic metabolic products generation and improve nutritional status. We hypothesized that very-low protein diet (VLPD) supplemented with KA/EAA may influence arterial wall stiffness and affect AVF maturation rates and duration in pre-dialysis ESRD patients.

Methods

In a prospective, cohort, 3 years study we enrolled 67 consecutive non-diabetic early referral ESRD patients that underwent AVF creation in our hospital. Patients were divided in two groups based on their regimen 12 months prior to surgery: a VLPD supplemented with KA/EAA study group versus a low protein diet non-KA/EAA-supplemented control group. For each patient we performed serum analysis for the parameters of bone mineral disease, inflammation and nutritional status, one pulse wave velocity (PWV) measurement and one Doppler ultrasound (US) determination prior the surgery, followed by consequent Doppler US assessments at 4, 6, 8 and 12 weeks after it. Rates and duration of mature AVF achievement were noted. We used logistic regression to analyze the association between AVF maturation and KA/EAA administration, by comparing rates and durations between groups, unadjusted and adjusted for systolic blood pressure, C-reactive protein, PWV, phosphorus values. All parameters in the logistic model were transformed in binary variables. A p-value < α = 0.05 was considered significant; data were processed using SPSS 16 software and Excel.

Results

In the study group (n = 28, aged 57 ± 12.35, 13 females) we registered better serum phosphate (p = 0.022) and C-reactive protein control (p = 0.021), lower PWV (p = 0.007) and a higher percent of AVF creation success (33.3 % versus 17.8 %, p < 0.05). AVF maturation duration was lower in study group (5.91 versus 7.15 weeks, p < 0.001).

Conclusions

VLPD supplemented with KA/EAA appear to improve the native AVF primary outcome, decreasing the initial vascular stiffness, possible by preserving vascular wall quality in CKD patients through a better serum phosphate levels control and the limitation of inflammatory response.

Preoperative Vascular Medial Fibrosis and Arteriovenous Fistula Development

BACKGROUND AND OBJECTIVES

Arteriovenous fistula maturation requires an increase in the diameter and blood flow of the feeding artery and the draining vein after its creation. The structural properties of the native vessels may affect the magnitude of these changes. We hypothesized that an increase in the collagen content of the vascular media (medial fibrosis) preoperatively would impair vascular dilation and thereby, limit the postoperative increase in arteriovenous fistula diameter and blood flow and clinical arteriovenous fistula maturation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We enrolled 125 patients undergoing arteriovenous fistula creation between October of 2008 and April of 2012 and followed them prospectively. Any consenting subject was eligible. Arterial and venous specimens were sampled during arteriovenous fistula surgery. Masson's trichrome-stained samples were used to quantify medial fibrosis. Arteriovenous fistula diameter and blood flow were quantified using 6-week postoperative ultrasound. Clinical arteriovenous fistula maturation was assessed using a predefined protocol. The association of preexisting vascular medial fibrosis with arteriovenous fistula outcomes was evaluated after controlling for baseline demographics, comorbidities, and the preoperative venous diameter.

RESULTS

The mean medial fibrosis was 69%±14% in the arteries and 63%±12% in the veins. Arterial medial fibrosis was associated with greater increases in arteriovenous fistula diameter (Δdiameter =0.58 mm; 95% confidence interval [95% CI], 0.27 to 0.89 mm; P<0.001) and arteriovenous fistula blood flow (Δblood flow =85 ml/min; 95% CI, 19 to 150 ml/min; P=0.01) and a lower risk of clinical arteriovenous fistula nonmaturation (odds ratio, 0.71; 95% CI, 0.51 to 0.99; P=0.04), all per 10% absolute difference in medial fibrosis. In contrast, venous medial fibrosis was not associated with the postoperative arteriovenous fistula diameter, blood flow, or clinical maturation.

CONCLUSIONS

Preoperative arterial medial fibrosis was associated with greater arteriovenous fistula diameter and blood flow and a lower risk of clinical arteriovenous fistula nonmaturation. This unexpected observation suggests that medial fibrosis promotes arteriovenous fistula development by yet undefined mechanisms or alternatively, that a third factor promotes both medial fibrosis and arteriovenous fistula maturation.

New Insights into Dialysis Vascular Access: Impact of Preexisting Arterial and Venous Pathology on AVF and AVG Outcomes

Despite significant improvements in preoperative patient evaluation and surgical planning, vascular access failure in patients on hemodialysis remains a frequent and often unforeseeable complication. Our inability to prevent this complication is, in part, because of an incomplete understanding of how preexisting venous and arterial conditions influence the function of newly created arteriovenous fistulas and grafts. This article reviews the relationship between three preexisting vascular pathologies associated with CKD (intimal hyperplasia, vascular calcification, and medial fibrosis) and hemodialysis access outcomes. The published literature indicates that the pathogenesis of vascular access failure is multifactorial and not determined by any of these pathologies individually. Keeping this observation in mind should help focus our research on the true causes responsible for vascular access failure and the much needed therapies to prevent it.

New Insights into Dialysis Vascular Access: What Is the Optimal Vascular Access Type and Timing of Access Creation in CKD and Dialysis Patients?

Optimal vascular access planning begins when the patient is in the predialysis stages of CKD. The choice of optimal vascular access for an individual patient and determining timing of access creation are dependent on a multitude of factors that can vary widely with each patient, including demographics, comorbidities, anatomy, and personal preferences. It is important to consider every patient's ESRD life plan (hence, their overall dialysis access life plan for every vascular access creation or placement). Optimal access type and timing of access creation are also influenced by factors external to the patient, such as surgeon experience and processes of care. In this review, we will discuss the key determinants in optimal access type and timing of access creation for upper extremity arteriovenous fistulas and grafts.

Arterial Disease and Vascular Access in Diabetic Patients

Purpose

There are conflicting reports on the effects of diabetes on the outcomes of hemodialysis access procedures. While some found no negative effects, others reported deleterious effects of diabetes on vascular access outcomes. Why is there concern about diabetes and related vascular problems on vascular access procedures? What are the differences of diabetic patients and their vasculature from that of nondiabetics? Do they have an effect on hemodialysis vascular access outcomes? We will try to find answers to these questions in light of the available evidence.

Methods

Recent literature on arterial disease in diabetes and end-stage renal disease (ESRD), and the effects on vascular access outcomes were searched in order to find answers to above questions.

Results

There are conflicting and controversial reports on the effects of preexisting vascular problems due to diabetes and chronic kidney disease (CKD) on the outcomes of hemodialysis access procedures. Diabetic vasculature, especially in patients with ESRD, has some specific problems, the most important of which seem to be the calcification and stiffening of the arteries.

Conclusions

Although some authors report inferior outcomes of vascular access procedures in diabetic patients, there is evidence that most of the problems encountered can be dealt with by careful patient selection, surgical skill, and experience.

Systematic Review of Drug Eluting Balloon Angioplasty for Arteriovenous Haemodialysis access Stenosis

Background

Native or prosthetic arteriovenous (AV) fistulas are preferred for permanent haemodialysis (HD) access. These are marked with circuit steno-occlusive disease leading to dysfunction or even failure. Late failure rates have been reported as high as 50%. Standard angioplasty balloons are an established percutaneous intervention for HD access stenosis. Reported restenosis rates remain high and practice guidelines recommend a wide 6-month primary patency (PP) of at least 50% for any intervention. Neointimal hyperplasia is one of the main causes for access circuit stenosis. Drug eluting balloon (DeB) angioplasty has been proposed as an alternative intervention to reduce restenosis by local drug delivery and possible inhibition of this process.

Purpose

To systematically assess the reported efficacy and safety of DeB angioplasty in percutaneous management of prosthetic and autologous HD access stenosis.

Methods

Protocol for the review was developed following the PRISMA-P 2015 statement. An electronic database (Medline, EMBASE, Clinical Trials.gov and Cochrane CENTRAL) search was conducted to identify articles reporting on the use of DeB intervention in HD AV access. Backward and forward citation search as well as grey literature search was performed. The MOOSE statement and PRISMA 2009 statement were followed for the reporting of results. Data from the included studies comparing DeBs with non-DeBs were pooled using a random effects metaanalysis model and reported separately on randomised and non-randomised studies.

Results

Six studies reported on 254 interventions in 162 participants (mean 27 ± 10 SD). The pooled mean and median duration of follow-up was 12 and 13 months (range 6-24 months). These comprised two randomised control trials (RCTs) and four cohort studies. Participant's mean age was 64 ± 5 years and 61% were male. Target lesions (TLs) ranged from under 2 mm to 5.9 mm and 51 were reported as de novo stenosis. Device failure described as wasting of the DeB was reported in two studies (55% and 92.8%). At 6 months TL PP was reported between 70% to 97% for DeBs in the RCTs and cohort studies, and 0% to 26% for non-DeBs. TLs treated with DeBs were associated with a higher primary patency at 6 months as compared to non-DeB balloons (RCTs: odds ratio [OR] 0.25, 95% CI 0.08 to 0.77 and I2 = 19%, cohort studies: OR 0.10, 95% CI 0.03 to 0.31 and an I2 = 20%). No procedure-related major or minor complications were reported.

Conclusions

Current literature reports DeBs as being safe and may convey some benefit in terms of improved rate of restenosis when used to treat AV access disease. However, this body of evidence is small and clinically heterogeneous. A large multicentre RCT may help to clarify the role of DeBs in the percutaneous treatment of AV HD access stenosis.

Aortic Arch Calcification Predicts Patency Loss of Arteriovenous Fistula in End-Stage Renal Disease Patients

Aortic arch calcification (AAC) is recognized as an important cardiovascular risk factor in patients with end-stage renal disease (ESRD). The aim of the study was to evaluate the impact of AAC grade on patency rates of arteriovenous fistula (AVF) in this specific population. The data of 286 ESRD patients who had an initial AVF placed were reviewed. The extent of AAC identified on chest radiography was divided into four grades (0–3). The association between AAC grade, other clinical factors, and primary patency of AVF was then analyzed by Cox proportional hazard analysis. The multivariate analysis demonstrated that the presence of AAC grade 2 (hazard ratio (95% confidence interval): 1.80 (1.15–2.84); p = 0.011) and grade 3 (3.03 (1.88–4.91); p < 0.001), and higher level of intact-parathyroid hormone (p = 0.047) were associated with primary patency loss of AVF. In subgroup analysis, which included AVF created by a surgeon assisted with preoperative vascular mapping, only AAC grade 3 (2.41 (1.45–4.00); p = 0.001), and higher intact-parathyroid hormone (p = 0.025) level were correlated with AVF patency loss. In conclusion, higher AAC grade and intact-parathyroid hormone level predicted primary patency loss of AVF in an ESRD population.