Hemodialysis Vascular Access Dysfunction: Molecular Mechanisms and Treatment

The rodent models of arteriovenous fistula

Arteriovenous fistulas (AVFs) have long been used as dialysis access in patients with end-stage renal disease; however, their maturation and long-term patency still fall short of clinical needs. Rodent models are irreplaceable to facilitate the study of mechanisms and provide reliable insights into clinical problems. The ideal rodent AVF model recapitulates the major features and pathology of human disease as closely as possible, and pre-induction of the uremic milieu is an important addition to AVF failure studies. Herein, we review different surgical methods used so far to create AVF in rodents, including surgical suturing, needle puncture, and the cuff technique. We also summarize commonly used evaluations after AVF placement. The aim was to provide recent advances and ideas for better selection and induction of rodent AVF models. At the same time, further improvements in the models and a deeper understanding of AVF failure mechanisms are expected.

Treatment of intragraft stenosis in hemodialysis grafts with Supera stents: A retrospective study

PURPOSE

To report the patency rates after implantation of an interwoven nitinol stent to salvage failing arteriovenous grafts (AVGs) caused by intragraft stenoses.

METHODS

Between May 2018 and May 2020, 21 Supera stents were placed in 20 patients (18 women; mean age: 79.9 years) who had a failing AVG due to repeat intragraft stenoses. Recurrent AVG dysfunction with same intragraft stenosis within 3 months after first time angioplasty was a criterion for stenting. Those with concurrent treatment for other lesions were excluded.

RESULTS

The technical success rate was 100%. Intragraft stenoses were treated at a median of 19.7 (interquartile range: 6-36) months after graft creation. Access circuit primary patency rates after stent placement were 84% and 35% at 6 and 12 months, respectively. Access circuit secondary patency rates were 100% at 6 and 12 months and 89% at 18 months. Only one patient presented with graft failure due to proximal drainage vein occlusion. The target lesion patency rates were 100% at 6 months and 75% at 12 months. The rate of reintervention for intragraft lesion was 0.15 procedures per year. Stent distortion did not occur under regular cannulation.

CONCLUSION

The interwoven nitinol stent is a promising treatment for failing AVGs with recurrent intragraft stenoses. The 1-year access circuit primary, secondary, and target lesion patency rates were acceptable, with a low reintervention rate. Stent fracture does not occur in areas of needle puncture.

Association of Permanent Vascular Access Dysfunction with Subsequent Risk of Cardiovascular Disease: A Population-Based Cohort Study

A functional permanent vascular access (VA) is required to perform a successful hemodialysis procedure. Hemodialysis VA dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population. Cardiovascular disease (CVD) is the leading cause of death in patients receiving chronic hemodialysis. Information about CVD associated with hemodialysis VA dysfunction is unclear. We analyzed the association between dialysis VA dysfunction and the risk of developing CVD in hemodialysis patients. This nationwide population-based cohort study was conducted using data from the National Health Insurance Research Database in Taiwan. One million subjects were sampled from 23 million beneficiaries and data was collected from 2000 to 2013. Patients with end-stage renal disease who had received permanent VA construction and hemodialysis and were aged at least 20 years old from 2000 to 2007 were included in the study population. The primary outcome was CVD, as defined by ICD-9-CM codes 410–414 and 430–437. A total of 197 individuals with permanent VA dysfunction were selected as the test group, and 100 individuals with non-permanent VA dysfunction were selected as the control group. Compared with the control group, the adjusted hazard ratio of CVD for the VA dysfunction group was 3.05 (95% CI: 1.14–8.20). A Kaplan–Meier analysis revealed that the cumulative incidence of CVD was higher in the permanent VA dysfunction group than in the comparison group. Permanent VA dysfunction is significantly associated with an increased risk of subsequent CVD.

Drug Coated Balloons for Dysfunctional Haemodialysis Venous Access: A Patient Level Meta-Analysis of Randomised Controlled Trials

OBJECTIVE

To perform an individual patient data level meta-analysis of randomised controlled trials comparing drug coated balloon angioplasty (DCB) against conventional percutaneous transluminal angioplasty (PTA) in the treatment of dysfunctional haemodialysis venous access.

METHODS

A search was conducted from inception to 13 November 2020. Kaplan-Meier curves comparing DCB with PTA by target lesion primary patency (TLPP) and access circuit primary patency (ACPP) were graphically reconstructed to retrieve patient level data. One stage meta-analyses with Cox models with random effects shared frailties were conducted to determine hazard ratios (HRs). Dynamic restricted mean survival times (RMST) were conducted in view of violation of the proportional hazards assumption. Conventional two stage meta-analyses and network meta-analyses under random effects Frequentist models were conducted to determine overall and comparative outcomes of paclitaxel concentrations used. Where outliers were consistently detected through outlier and influence analyses, sensitivity analyses excluding those studies were conducted.

RESULTS

Among 10 RCTs (1 207 patients), HRs across all models favoured DCB (one stage shared frailty HR 0.62, 95% CI 0.53 - 0.73, p < .001; two stage random effects HR 0.60, 95% CI 0.42 - 0.86, p = .018, I² = 65%) for TLPP. Evidence of time varying effects (p = .005) was found. TLPP RMST was + 3.54 months (25.0%) longer in DCB treated patients compared with PTA (p = .001) at three years. TLPP at six months, one year, and two years was 75.3% vs. 58.1%, 51.1% vs. 37.1%, and 31.4% vs. 26.0% for DCB and PTA, respectively. The P-Scores within the Frequentist network meta-analysis suggest that higher concentrations of paclitaxel were associated with better TLPP and ACPP. Among six RCTs (854 patients), the one stage model favoured DCB (shared frailty HR 0.72, 95% CI 0.60 - 0.87, p < .001) for ACPP. Conversely, the two stage random effects model demonstrated no significant difference (HR 0.76, 95% CI 0.35 - 1.67, p = .41, I² = 81%). Sensitivity analysis excluding outliers significantly favoured DCB (HR 0.61, 95% CI 0.41 - 0.91, p = .027, I² = 62%).

CONCLUSION

Overall evidence suggests that DCB is favoured over PTA in TLPP and ACPP.

Comparison of functional patency rates between paclitaxel-eluting versus plain balloon angioplasty in hemodialysis patients with central venous stenosis: An intra-individual comparison study

Central venous stenosis (CVS) is usually a late-diagnosed clinical entity that is common in hemodialysis patients. It causes various problems ranging from hemodialysis difficulty to loss of the arterio-venous (A-V) fistula. In the present study, we aimed to determine the effect of drug eluting balloon while excluding the influence of other variable factors by evaluating the same individuals with plain and paclitaxel-eluting balloons. This research was a prospective study of 18 symptomatic hemodialysis patients (age 50.9 ± 14.0 years, range 32-72 years; 11 male, 7 female) with CVS who underwent treatment by plain balloon angioplasty (PBA) and paclitaxel-eluting balloon angioplasty (PEBA) in our hospital from January 2016 to June 2017. First, third and sixth month central vein patency rates were compared. The median patency rates of central veins were 109.0 (range: 10-324) days after PBA and 238.5 (range: 157-501) days after PEBA (p < 0.001). There was no statistically significant difference between PBA and PEBA angioplasty in one-month patency (p ˃ 0.05). By contrast, a statistically significant difference was found between 3- and 6-month patency rates (p = 0.031 and p ˂ 0.001, respectively). Kaplan-Meier analysis revealed that the primary cumulative patency rate of PEBA was significantly longer than that of PBA (p ˂ 0.001). In this prospective study, PEBA patency is superior to PBA patency in the treatment of CVS in dialysis patients.

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.

Efficacy of Primary Stent-Graft Placement in the Treatment of Vascular Access Graft Outflow Tract Stenosis

PURPOSE

The aim of this study is to present our personal experience using covered nitinol stent-graft in the treatment of outflow tract stenosis of arteriovenous grafts (AVGs) for hemodialysis access.

MATERIALS AND METHODS

Between May 2015 and October 2017, we retrospectively evaluated 36 (24 males, 12 females; mean age: 65.6 years) patients with AVGs on hemodialysis who underwent percutaneous angioplasty followed by endovascular stent-graft deployment for the treatment of stenosis of the venous outflow of the AVG. Indication for treatment included early restenosis (<3 months after previous percutaneous transluminal angioplasty [PTA]), long stenosis (stenoses >50% extending for a length >5 cm), and recoil of the stenosis after PTA performed with a noncompliant high-pressure balloon. Of 36 patients, 27 (75%) required surgical thrombectomy prior to endovascular procedure. Technical success, clinical success, primary and secondary patency, and safety were evaluated.

RESULTS

Technical success was 100%, and clinical success was 94.4%. Primary patency was 94.4%, 72.2%, 63%, 45.9%, and 45.9% at 1, 3, 6, 12, and 18 months (average: 215 days, range: 9-653 days); secondary patency was 94.4% and 86.1% at 1 and 3 months; 80.4% at 6, 12, and 18 months; and 53.6% at 24 months (average: 276.8 days, range: 9-744 days). No deaths were registered.

CONCLUSIONS

In selected cases, the use of stent-graft represents an effective and safe solution for the treatment of stenotic complications of the venous outflow of AVGs, even in the setting of access thrombosis.

Near-Infrared Fluorescence Imaging of Matrix Metalloproteinase 2 Activity as a Biomarker of Vascular Remodeling in Hemodialysis Access

PURPOSE

To establish the capability of near-infrared fluorescence (NIRF) imaging for the detection of matrix metalloproteinase 2 (MMP-2) activity as a biomarker of vascular remodeling (VR) in arteriovenous fistulae (AVFs) in vivo.

MATERIALS AND METHODS

AVFs were created in the right groins of Wistar rats (n = 10), and sham procedures were performed in the contralateral groins. Fistulography via a left common carotid artery approach confirmed stenosis (> 50%) in a subset of animals (n = 5) 4 weeks after AVF creation. After administration of MMP-2-activated NIRF probe, near-infrared imaging was performed in vivo and ex vivo of both the AVF and the sham-treated vessels to measure radiant efficiency of MMP-2-activated NIRF signal over background. Histologic analyses of AVF and sham-treated vessels were performed to measure VR defined as inward growth of the vessel caused by intimal thickening.

RESULTS

AVFs demonstrated a significantly higher percentage increase in radiant efficiency over background compared with sham vessels (45.5 ± 56% vs 16.1 ± 17.8%; P = .008). VR in AVFs was associated with increased thickness of neointima staining positively for MMP-2 (161.8 ± 45.5 μm vs 73.2 ± 36.7 μm; P = .01). A significant correlation was observed between MMP-2 activity as measured by relative increase in radiant efficiency for AVFs and thickness of neointima staining positively for MMP-2 (P = .039).

CONCLUSIONS

NIRF imaging can detect increased MMP activity in remodeled AVFs compared with contralateral sham vessels. MMP-2-activated NIRF signal correlates with the severity of intimal thickening. These findings suggest NIRF imaging of MMP-2 may be used as a biomarker of the vascular remodeling underlying stenosis.

Randomized pilot study to compare metal needles versus plastic cannulae in the development of complications in hemodialysis access

BACKGROUND

Hemodialysis requires needle insertions every treatment. Needle injury (mechanical or hemodynamic) may cause complications (aneurysms/stenosis) that compromise dialysis delivery requiring interventions. Metal needles have a sharp slanted "V"-shaped cutting tip; plastic cannulae have a dull round tip and four side holes. Preliminary observations demonstrated a difference in intradialytic blood flow images and mean Doppler velocities at cannulation sites between the two devices. Complications from mechanical and hemodynamic trauma requiring interventions were compared in each group.

MATERIALS AND METHODS

In all, 33 patients (13 females and 17 new accesses) were randomized to metal group (n = 17) and plastic group (n = 16). Mechanical trauma was minimized by having five nurses performing ultrasound-guided cannulations. Complications were identified by the clinician and addressed by the interventionalists, both blinded to study participation. Patients were followed for up to 12 months.

RESULTS

Baseline characteristics were not significant. Procedures to treat complications along cannulation segments increased from 0.41 to 1.29 per patient (metal group) and decreased from 1.25 to 0.69 per patient (plastic group; p = 0.004). The relative risks of having an intervention (relative risk = 1.5, 95% confidence interval = 0.88-2.67) and having an infiltration during hemodialysis (relative risk = 2.26, 95% confidence interval = 1.03-4.97) were higher for metal needles. Time to first intervention trended in favor of plastic cannula (p = 0.069). Cost of supplies for these interventions was approximately CAD$20,000 lower for the plastic group.

CONCLUSION

Decreased burden of illness related to cannulation (less infiltrations during hemodialysis) and Qb were associated with plastic cannulae. Decreased procedure costs were suggested during the study period in the plastic group.

Usefulness of paclitaxel-releasing high-pressure balloon associated with cutting balloon angioplasty for treatment of outflow stenoses of failing hemodialysis arteriovenous shunts

AIM

To evaluate the technical and clinical success, primary patency (PP) and complications of angioplasty performed with paclitaxel-coated balloon (PCBs) associated with cutting balloon and for the treatment of the outflow stenoses of failing hemodialysis arteriovenous shunt.

MATERIAL AND METHODS

From September 2014 to September 2015, 50 patients with 66 stenoses were registered. Vascular accesses were autogenous (n = 20) and prosthetic (n = 30). Stenosis were documented during follow-up with routine echo-color Doppler, clinical evaluation and in the remaining incidentally during fistulography. Angioplasty was performed with cutting balloon and afterward with PCB. The mean follow-up time was 8 months (range 6-15 months). Technical success, clinical success, primary patency and complications were registered.

RESULTS

Technical success was 100 %. Clinical success was 94.7 %. Primary patency rate was 87.7 %; in five patients, a significant re-stenosis (≥50 %) was registered. A residual asymptomatic stenosis (<30 %) was registered in four cases (7 %). No major complications were registered.

CONCLUSIONS

A short-term patency benefit may be obtained including PCB in angioplasty treatment of failing hemodialysis arteriovenous shunts.

Impact of Needles in Vascular Access for Hemodialysis

This article reviews pragmatic aspects of cannulation practice and types of cannulation devices, as well as their impact in vascular access for hemodialysis. Hemodialysis treatment requires successful insertion of two needles for each dialysis treatment. The first needle is the arterial needle; it removes blood with toxin accumulation from the patient and delivers it to the dialysis machine. The second needle, called the venous needle, returns the purified blood from the dialyzer to the patient. Mechanical and hemodynamic trauma related to needle insertions will be discussed.

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.

Postintervention Patency Rates and Predictors of Patency after Percutaneous Interventions on Intragraft Stenoses within Failing Prosthetic Arteriovenous Grafts

PURPOSE

To determine postintervention patency rates after endovascular interventions on intragraft stenosis within failing prosthetic arteriovenous (AV) grafts, as well as predictors of patency.

MATERIALS AND METHODS

Retrospective review of percutaneous interventions on prosthetic AV grafts presenting with first-time intragraft stenoses over a 7-year period revealed 183 patients (81 male; mean age, 59.7 y). "Intragraft" was defined as 2 cm or more from the arterial or venous anastomosis. Procedural imaging was retrospectively reviewed. Patency rates were estimated by Kaplan-Meier test. Predictors of patency were calculated by Cox proportional-hazards model.

RESULTS

Two-hundred twenty-nine intragraft stenoses were identified in 183 grafts. Intragraft stenoses were treated at a median of 20.7 months (interquartile range, 12.0-33.9 mo) after graft creation. Graft thrombosis was present in 62%. The anatomic success rate of angioplasty was 85%. Fifteen percent required stent or stent-graft deployment because of inadequate response to angioplasty. A concurrent nonintragraft stenosis within the access circuit was identified in 76% of grafts. At 3, 6, and 12 months, postintervention primary patency rates were 56%, 40%, and 23%, respectively. Secondary patency rates were 84%, 77%, and 67%, respectively. The lesion-specific patency rates were 89, 75%, and 63%, respectively. Graft thrombosis (hazard ratio [HR], 1.43; P = .048) and concurrent nonintragraft lesion (HR, 1.51; P = .047) were independent negative predictors of primary patency. Graft thrombosis (HR, 1.81; P = .029) was a negative predictor of lesion patency, and stent or stent-graft deployment (HR, 0.42; P = .045) was a positive predictor of lesion patency.

CONCLUSIONS

Endovascular interventions on intragraft stenoses resulted in primary, secondary, and lesion-specific patency rates of 40%, 77%, and 75%, respectively, at 6 months. Stent or stent-graft deployment may prolong lesion patency.

Evaluation of Percutaneous Transluminal Angioplasty Screening using Color Doppler Ultrasonography

Purpose

Well-functioning vascular access is important in hemodialysis patients. The aim of this study was to assess stenosis using color Doppler ultrasonography as well as to investigate a possible association between the need for percutaneous transluminal angioplasty and hemodynamic parameters.

Methods

A prospective study of the medical records of color Doppler ultrasonography routine examinations of 372 patients was conducted at a dialysis satellite clinic in Japan. Data were analyzed using logistic regression analysis and the receiver operating characteristic curve. The cutoff point for hemodynamic parameters was determined to explore the predictors of percutaneous transluminal angioplasty.

Results

Logistic regression analysis showed that brachial artery flow volume, brachial artery resistance index and puncture point flow volume divided by the quantity of dialysis blood flow rate were independently associated with percutaneous transluminal angioplasty. Brachial artery resistance index over 0.61, brachial artery blood flow volume under 665 mL/min and puncture point flow volume divided by dialysis blood flow rates under 1.25 were predictive values of the need for percutaneous transluminal angioplasty.

Conclusions

These parameters could be used as markers for assessing percutaneous transluminal angioplasty risk in hemodialysis patients.

Vein graft adaptation and fistula maturation in the arterial environment

Veins are exposed to the arterial environment during two common surgical procedures, creation of vein grafts and arteriovenous fistulae (AVF). In both cases, veins adapt to the arterial environment that is characterized by different hemodynamic conditions and increased oxygen tension compared with the venous environment. Successful venous adaptation to the arterial environment is critical for long-term success of the vein graft or AVF and, in both cases, is generally characterized by venous dilation and wall thickening. However, AVF are exposed to a high flow, high shear stress, low-pressure arterial environment and adapt mainly via outward dilation with less intimal thickening. Vein grafts are exposed to a moderate flow, moderate shear stress, high-pressure arterial environment and adapt mainly via increased wall thickening with less outward dilation. We review the data that describe these differences, as well as the underlying molecular mechanisms that mediate these processes. Despite extensive research, there are few differences in the molecular pathways that regulate cell proliferation and migration or matrix synthesis, secretion, or degradation currently identified between vein graft adaptation and AVF maturation that account for the different types of venous adaptation to arterial environments.

Blood monocyte count may be a predictor of vascular access failure in hemodialysis patients

It has been reported that an increase in the counts of white blood cells (WBC) and their subpopulations is an independent predictor of atherosclerotic events and mortality. On the other hand, vascular access (VA) stenosis is caused by a progressive development of neointimal hyperplasia. We examined the relationship between VA failure and counts of peripheral WBC and their subpopulations in hemodialysis (HD) patients. The study population consisted of 82 patients undergoing regular HD. Twenty-two patients, who were unstable, were excluded from the study. After one year, we examined the relationship between VA failure and the counts of peripheral WBC and their subpopulations. In the follow-up period, 21 patients had complicated VA failure. The counts of WBC, neutrophils, lymphocytes, eosinophils, and basophils did not show a significant difference, but a monocyte count of ≥ 400/μL was shown to indicate a high probability of VA failure. Logistic regression analysis revealed that monocyte count was an independent risk factor of VA failure. The peripheral blood monocyte count may be a predictor of VA failure in HD patients.