Statin therapy is not associated with improved vascular access outcomes

Bioengineering Strategies for Treating Neointimal Hyperplasia in Peripheral Vasculature: Innovations and Challenges

Neointimal hyperplasia, a pathological response to arterial interventions or injury, often leads to restenosis and recurrent narrowing or occlusion, particularly in the peripheral vasculature. Its prevalence and negative impact on the long-term success of vascular interventions have driven extensive research aimed at better understanding the condition and developing effective therapies. This review provides a comprehensive overview of emerging bioengineering strategies for treating neointimal hyperplasia in peripheral vessels. These approaches include novel therapeutics and cell-based technologies designed to promote re-endothelialization, modulate vascular smooth muscle cell (VSMC) phenotype, reduce inflammation, scavenge reactive oxygen species (ROS), and enhance biomechanical compatibility between grafts and native vessels. Furthermore, advanced therapeutic delivery modalities are highlighted for their potential to achieve targeted, localized treatment at injury sites. This review also explores underrepresented therapeutic targets beyond traditional approaches, offering new opportunities for intervention. The multifaceted examination underscores the challenge of neointimal hyperplasia and presents a promising roadmap toward more effective treatments, ultimately aiming to improve patient outcomes after vascular interventions.

Periadventitial biomaterials to improve arteriovenous fistula and graft outcomes

Periadventitial biomaterials have been employed for nearly three decades to promote adaptive venous remodeling following hemodialysis vascular access creation in preclinical models and clinical trials. These systems are predicated on the combination of scaffolds, hydrogels, and/or particles with therapeutics (small molecules, proteins, genes, and cells) to prevent venous stenosis and subsequent maturation failure. Periadventitial biomaterial therapies have evolved from simple drug delivery vehicles for traditional drugs to more thoughtful designs tailored to the pathophysiology of access failure. The emergence of tissue engineering strategies and gene therapies are another exciting new direction. Despite favorable results in experimental and preclinical studies, no periadventitial therapy has been clinically approved to improve vascular access outcomes. After conducting an exhaustive review of the literature, we identify the seminal studies and clinical trials that utilize periadventitial biomaterials and discuss the key features of each biomaterial format and their respective shortcomings as they pertain to access maturation. This review provides a foundation from which clinicians, surgeons, biologists, and engineers can refer to and will hopefully inspire thoughtful, translatable treatments to finally address access failure.

Plasma Interleukin-6 Level Predicts the Risk of Arteriovenous Fistula Dysfunction in Patients Undergoing Maintenance Hemodialysis

Systemic inflammation has been proposed as a relevant factor of vascular remodeling and dysfunction. We aimed to identify circulating inflammatory biomarkers that could predict future arteriovenous fistula (AVF) dysfunction in patients undergoing hemodialysis. A total of 282 hemodialysis patients were enrolled in this prospective multicenter cohort study. Plasma cytokine levels were measured at the time of data collection. The primary outcome was the occurrence of AVF stenosis and/or thrombosis requiring percutaneous transluminal angioplasty or surgery within the first year of enrollment. AVF dysfunction occurred in 38 (13.5%) patients during the study period. Plasma interleukin-6 (IL-6) levels were significantly higher in patients with AVF dysfunction than those without. Diabetes mellitus, low systolic blood pressure, and statin use were also associated with AVF dysfunction. The cumulative event rate of AVF dysfunction was the highest in IL-6 tertile 3 (p = 0.05), and patients in tertile 3 were independently associated with an increased risk of AVF dysfunction after multivariable adjustments (adjusted hazard ratio = 3.06, p = 0.015). In conclusion, circulating IL-6 levels are positively associated with the occurrence of incident AVF dysfunction in hemodialysis patients. Our data suggest that IL-6 may help clinicians identify those at high risk of impending AVF failure.

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.

Arteriovenous Fistula Surveillance Using Tomographic 3D Ultrasound

OBJECTIVE

A well functioning arteriovenous fistula (AVF) is essential for haemodialysis. Despite regular duplex ultrasound (DUS) a significant number of AVFs fail. Tomographic 3D ultrasound (tUS) creates a 3D image of the AVF that can be interpreted by the clinician. DUS, tUS, and fistulograms were compared for the identification and measurement of flow limiting stenosis.

METHODS

Patients with AVF dysfunction on routine Transonic surveillance, defined as (1) > 15% reduction in flow on two consecutive occasions, (2) > 30% reduction in flow on one occasion, (3) flow of < 600 mL/sec, (4) presence of recirculation, underwent DUS. AVF tUS imaging was performed prior to fistulography. All fistulograms were reported by the same consultant radiologist and tUS images by the same vascular scientist blinded to the fistulogram results. Maximum diameter reduction in all stenoses were measured using all three imaging techniques.

RESULTS

In 97 patients with 101 stenoses, the mean (± standard deviation [SD]) severity of stenosis was 63.0 ± 13.9%, 65.0 ± 11.6%, and 64.8 ± 11.7% for the fistulograms, DUS, and tUS respectively. The mean (± SD) time between ultrasound and fistulography imaging was 15.0 ± 14.5 days. Assuming the fistulogram as the "gold standard", Bland-Altman agreement for DUS was -1.9 ± 15.5% (limit of agreement [LOA] -32.2 - 28.4) compared with -1.7 ± 15.4% (LOA -31.9 - 28.4) for tUS. Median (± interquartile range) time to complete the investigation was 09:00 ± 03:19 minutes for DUS and 03:13 ± 01:56 minutes for tUS (p < .001).

CONCLUSION

DUS and tUS were equally accurate at detecting AVF complications but tUS investigation requires less skill and was significantly quicker than DUS.

Statins Protect against Thrombosis of Cannulated Radiocephalic Fistulas in Diabetic Patients

BACKGROUND

Radiocephalic arteriovenous fistula (RCAVF) creation is the preferred first line hemodialysis access procedure. Analysis of diabetic rat arteriovenous fistula model indicates improved vascular function with HMG-CoA-Reductase Inhibitor (statin) use. We predict similar outcomes in diabetic patients undergoing primary RCAVF placement.

METHODS

A Veterans Administration Hospital dialysis access database over a 15-year period was queried identifying all RCAVF placements in diabetic patients. Patients were stratified into statin medication usage or not at RCAVF creation. Outcomes examined include rate of successful cannulation, functional patency duration, interventions per access, and rates of access thrombosis. Thrombosis-free survival of cannulated RCAVFs were compared using Kaplan-Meier method with log-rank analysis followed by univariate, stepwise logistic regression and ROC curve analysis.

RESULTS

Total number of 123 RCAVF cases were performed in 122 diabetic male patients. At the time of RCAVF placement, 92 cases were performed on patients that were taking statin medication and 31 cases were performed on patients that were not taking statin medication. There was no difference in terms of rate of successful cannulation, functional patency duration, and number of interventions per access between the statin and non-statin groups. However, rate of RCAVF thrombosis once accessed was significantly lower in the statin group compared to the non-statin group (P = 0.0005). Kaplan-Meier survival curve for each group were compared using log-rank test to reveal that diabetic patients who were on statin therapy at the time of operation had significantly higher access survival over time against thrombosis once it was cannulated for dialysis treatment compared to those who were not on statin therapy (P = 0.0003). Univariate, stepwise logistic regression model indicated statin use as the only significant factor associated with lack of thrombosis (P = 0.05).

CONCLUSIONS

Statins appear to have protective effects against RCAVF thrombosis as predicted in animal models for diabetic patients undergoing primary RCAVF placements. There were similar functional outcomes in terms of rate of successful cannulation, functional patency duration, and number of interventions per access. These data should encourage further investigation of statins and their role in hemodialysis access.

Vascular access management after percutaneous transluminal angioplasty using a calcium alginate sheet: a randomized controlled trial

BACKGROUND

Management of vascular access (VA) is essential in hemodialysis (HD) patients. However, VA often fails and percutaneous transluminal angioplasty (PTA) is required. Conventional hemostasis at the puncture site is associated with complications. This study aimed to analyze the efficacy and safety of a hemostatic wound dressing made of calcium alginate at the puncture site of VA after PTA and evaluate other factors affecting hemostasis.

METHODS

After PTA for VA, 200 HD patients were randomized to a calcium alginate sheet (CA) group (n = 100) or a no drug-eluting sheet (control) group (n = 100). We recorded time to hemostasis at the puncture site every 5 min, noting any complications.

RESULTS

In the CA group, rates of hemostatic achievement at 5, 10, 15 and >15 min were 57, 25, 8 and 10%, respectively. In the control group, the rates were 39, 28, 14 and 19%, respectively. Rates of hemostatic achievement at 5 min were significantly higher in the CA group (P = 0.01). In logistic regression analysis, factors affecting hemostasis within 5 min were use of the CA sheet [odds ratio (OR) 2.33; 95% confidence interval (CI) 1.26-4.37], platelet count ≤100 000/μL (OR 0.19; 95% CI 0.04-0.69), number of antithrombotic tablets used per day ≥1 tablet (OR 0.50; 95% CI 0.26-0.94) and upper arm VA (OR 0.16; 95% CI 0.03-0.55).

CONCLUSIONS

A CA sheet can safely reduce time to hemostasis at the puncture site after PTA, and should be considered for treating patients with a bleeding tendency.

Atorvastatin Reduces In Vivo Fibrin Deposition and Macrophage Accumulation, and Improves Primary Patency Duration and Maturation of Murine Arteriovenous Fistula

BACKGROUND

Arteriovenous fistulas placed surgically for dialysis vascular access have a high primary failure rate resulting from excessive inward remodeling, medial fibrosis, and thrombosis. No clinically established pharmacologic or perisurgical therapies currently address this unmet need. Statins' induction of multiple anti-inflammatory and antithrombotic effects suggests that these drugs might reduce arteriovenous fistula failure. Yet, the in vivo physiologic and molecular effects of statins on fistula patency and maturation remain poorly understood.

METHODS

We randomized 108 C57Bl/6J mice to receive daily atorvastatin 1.14 mg/kg or PBS (control) starting 7 days before end-to-side carotid artery-jugular vein fistula creation and for up to 42 days after fistula creation. We then assessed longitudinally the effects of statin therapy on primary murine fistula patency and maturation. We concomitantly analyzed the in vivo arteriovenous fistula thrombogenic and inflammatory macrophage response to statin therapy, using the fibrin-targeted, near-infrared fluorescence molecular imaging agent FTP11-CyAm7 and dextranated, macrophage-avid nanoparticles CLIO-VT680.

RESULTS

In vivo molecular-structural imaging demonstrated that atorvastatin significantly reduced fibrin deposition at day 7 and macrophage accumulation at days 7 and 14, findings supported by histopathologic and gene-expression analyses. Structurally, atorvastatin promoted favorable venous limb outward remodeling, preserved arteriovenous fistula blood flow, and prolonged primary arteriovenous fistula patency through day 42 (P<0.05 versus control for all measures).

CONCLUSIONS

These findings provide new in vivo evidence that statins improve experimental arteriovenous fistula patency and maturation, indicating that additional clinical evaluation of statin therapy in patients on dialysis undergoing arteriovenous fistula placement is warranted.

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.

The Effect of Aspirin on Preventing Vascular Access Dysfunction in Incident Hemodialysis Patients: A Prospective Cohort Study in Korean Clinical Research Centers for End-Stage Renal Disease (CRC for ESRD)

Background: Aspirin is often prescribed empirically to improve the patency of hemodialysis (HD) vascular access. Therefore, this study aimed to investigate the impact of aspirin on the survival of vascular access in incident HD patients with arteriovenous fistula (AVF) or arteriovenous graft (AVG). Methods: A prospective cohort of 881 incident HD patients was enrolled between 2009 and 2014. The primary outcome was defined as the first AVF/AVG intervention or salvage procedure, including percutaneous transluminal angioplasty or surgery for vascular access failure. Cox analyses were performed to determine the association between aspirin usage and the occurrence of the primary outcome. Results: The mean age of the patient group was 57.9 ± 13.4, and 63.8% of the patients were male. Aspirin was prescribed in 241 (27.4%) patients, and the median follow-up duration was 30 months. During follow-up, 180 (20.4%) patients experienced the primary outcome event. Univariate analysis showed that age, gender, presence of diabetes mellitus (DM), preexisting peripheral arterial disease, and the type of vascular access used (AVG versus AVF) were significantly associated with the development of the primary outcome. However, aspirin usage from the baseline was not significantly associated with primary outcome events (hazard ratio (HR): 1.16; 95% confidence interval (CI): 0.84–1.60; p = 0.378). Multivariate analysis showed that gender, the presence of DM, and the type of vascular access were still significantly associated with the occurrence of the primary outcome. Moreover, we did not observe the protective effect of taking aspirin on primary vascular access failure, even in subgroup analyses stratified according to gender, the presence of DM, and the type of vascular access. Conclusion: Physicians should carefully consider when they prescribe aspirin for the prevention of primary vascular access failure in Korean incident HD patients. In addition, larger prospective interventional studies are needed to elucidate the effect of aspirin on vascular access failure.

Mineralocorticoid receptor: A hidden culprit for hemodialysis vascular access dysfunction

Hemodialysis vascular access dysfunction is a common and intractable problem in clinical practice with no definitive therapy yet available. As a key mediator of vascular and cardiac maladaptive remodeling, mineralocorticoid receptor (MR) plays a pivotal role in vascular fibrosis and intimal hyperplasia (IH) and is potentiated locally in hemodialysis vascular access following diverse injuries, like barotrauma, cannulation and shear stress. MR-related genomic and non-genomic pathways are responsible for triggering vascular smooth muscle cell activation, proliferation, migration and extracellular matrix overproduction. In endothelial cells, MR signaling diminishes nitric oxide production and its bioavailability, but amplifies reactive oxygen species, leading to an inflammatory state. Moreover, MR favors macrophage polarization towards a pro-inflammatory phenotype. In clinical settings like post-angioplasty or stenting restenosis, the beneficial effect of MR antagonists on vascular fibrosis and IH has been validated. In aggregate, therapeutic targeting of MR may provide a new avenue to prevent hemodialysis vascular access dysfunction.

Antiplatelet agents maintain arteriovenous fistula and graft function in patients receiving hemodialysis: A nationwide case-control study

Background

In this study, we evaluated the effects of various medications on the patency of vascular access (VA) for hemodialysis.

Methods

We analyzed data from the Longitudinal Health Insurance Database of Taiwan. We adopted a case–control study design within a cohort of patients who had received regular hemodialysis between 2002 and 2012; 34,354 patients with first VA failure were identified, and the duration from VA creation date to the first VA failure date was calculated. We then classified these patients into two groups, namely arteriovenous fistula (AVF, n = 25,933) and arteriovenous graft (AVG, n = 8,421). Each group was further divided into two subgroups, namely short-term (<1 year) and long-term (≥1 year) patency.

Results

The risk factors for early VA failure were age ≥65 years, diabetes mellitus, hyperlipidemia, cerebral vascular disease, congestive heart failure, peripheral artery disease, and sepsis. Male sex, hypertension, cancer, and peptic ulcer were associated with early AVF failure. Antiplatelet therapy increased the AVF and AVG patency times with adjusted odds ratios of 0.748 (95% confidence interval [CI]: 0.703–0.796, p < 0.0001) and 0.810 (95% CI: 0.728–0.901, p = 0.0001), respectively. A significant decrease in the VA failure risk was observed with an increase in the cumulative defined daily dose of antiplatelet agents.

Conclusion

This nationwide study demonstrated that some risk factors were associated with early VA failure and that the use of antiplatelet agents prevented the loss of VA patency in a dose–response manner. Thus, antiplatelet drugs should be routinely administered to high-risk patients receiving dialysis.

Statin therapy improved long-term prognosis in patients with major non-cardiac vascular surgeries: a systematic review and meta-analysis

OBJECTIVE

To investigate whether statin intervention will improve the long-term prognosis of patients undergoing major non-cardiac vascular surgeries.

METHODS

Major database searches for clinical trials enrolling patients undergoing major non-cardiac vascular surgeries, including lower limb revascularization, carotid artery surgeries, arteriovenous fistula, and aortic surgeries, were performed. Subgroup analyses, stratified by surgical types or study types, were employed to obtain statistical results regarding survival, patency rates, amputation, and cardiovascular and stroke events. Odds ratio (ORs) and 95% confidence intervals (CIs) were calculated by Review Manager 5.3. Sensitivity analysis, publication bias and meta-regression were conducted by Stata 14.0.

RESULTS

In total, 34 observational studies, 8 prospective cohort studies and 4 randomized controlled clinical trials (RCTs) were enrolled in the present analysis. It was demonstrated that statin usage improved all-cause mortality in lower limb, carotid, aortic and mixed types of vascular surgery subgroups compared with those in which statins were not used. Additionally, the employment of statins efficiently enhanced the primary and secondary patency rates and significantly decreased the amputation rates in the lower limb revascularization subgroup. Furthermore, for other complications, statin intervention decreased cardiovascular events in mixed types of vascular surgeries and stroke incidence in the carotid surgery subgroup. No significant publication bias was observed. The meta-regression results showed that the morbidity of cardiovascular disease or the use of aspirin might affect the overall estimates in several subgroups.

CONCLUSIONS

This meta-analysis demonstrated that statin therapy was associated with improved survival rates and patency rates and with reduced cardiovascular or stroke morbidities in patients who underwent non-cardiac vascular surgeries.

Restoration of Autologous Arteriovenous Fistula by Removal of the Occluded Short Venous Part and Venovenous End-To-End Anastomosis in a Hemodialysis Patient

Standard salvage procedures for occuluded autologous arteriovenous fistula (AVF) in a hemodialysis patient are endovascular and/or surgical therapy. When endovascular therapy and thrombectomy prove unsuccessful, it is most likely that creating a new AVF or arteriovenous graft will be considered. However, if the occuluded venous part is short, we have adopted an operative technique for repair of AVF by removal of the occluded short venous part and venovenous end-to-end anastomosis. To our knowledge, the efficacy and clinical course of restoration of AVF by the technique have not been reported to date. Here, we describe the technique and report the successful treatment of a hemodialysis patient who developed AVF occlusion.

Medical safety in the care of the person with end-stage kidney disease

Much is written about medical safety as it pertains to patients with chronic kidney disease, yet the transition to end-stage kidney disease and processes inherent to the receipt of dialysis present unique safety challenges in this population. Educational efforts in medical safety need to focus on the areas of greatest threat and where intervention can provide the greatest benefit. This study addresses such safety topics in the dialysis population and identifies potential strategies that may aid in harm reduction.

Preoperative management of arteriovenous fistula (AVF) for hemodialysis

Native arteriovenous fistula (AVF) is the favorite access for hemodialysis (HD). The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) recommends its creation in most patients with renal failure. Unfortunately, intensive efforts to promote native AVF in patients with marginal vessels have increased the rate of primary fistula failure. A non-functioning fistula prompts the use of central venous catheter (CVC) that, unlike AVF, has been associated with an increased risk of morbidity and mortality among patients receiving HD. We believe that successful and timely AVF placement relies on the development of a multidisciplinary integrated preoperative program divided into five stages: (i) management of patients with advanced chronic kidney disease (CKD), (ii) management of preoperative risk factors for AVF failure, (iii) planning of native AVF, (iv) assessment of patient eligibility and (v) preoperative vascular mapping. Focusing specifically on native AVF, we review scientific evidence regarding preoperative management of this vascular access in order to favor construction of long-term functioning fistula minimizing development of severe complications.

Impact of Statins on Arteriovenous Fistulas Outcomes: A Meta-Analysis

Statins are effective lipid-lowering drugs with beneficial pleiotropic effects for vascular remodeling processes, statins may have a beneficial effect on the function of arteriovenous fistulas (AVFs) in hemodialysis (HD) patients. Therefore, we performed this systematic review to assess the protective effects of statin therapy in HD patients. The randomized controlled trials (RCTs) or quasi-RCTs and retrospective cohort studies (RCS) of statin therapy for the function of AVFs in HD patients were searched from multiple databases. Relevant studies were screened according to predefined inclusion criteria and then pooled-analyses were performed using RevMan 5.2 software. One RCT and six RCS containing 20 246 HD patients were included in this meta-analysis, of whom 9847 were treated with statins and 10 399 were treated with placebo. Our meta-analysis showed that there was no significant difference between statins and placebo groups, with those who received statin therapy showing similar AVF failure rates compared to control (pooled risk ratio = 0.89; 95% CI, 0.70 to 1.12, P = 0.32), and there was obvious evidence of statistical heterogeneity (P = 0.005; I²  = 68%). In addition, subgroup pooled analyses revealed that statin therapy did not ameliorate AVF failure in participants from the same racial background or similar sample size trials. There was no evidence that statins therapy could reduce the AVFs failure. However, due to methodological limitations and obvious statistical heterogeneity, high-quality, long-term and multicenter trials are required to fully elucidate the clinical value of statins administration for the outcomes of AVFs in HD patients.

Efficacy of statin on vascular access patency in diabetic hemodialysis patients

INTRODUCTION

An effective approach to prevent hemodialysis vascular access dysfunction is still unclear despite previous studies, which have shown conflicting results of several drugs on vascular access outcomes. In this study, we focused on diabetic hemodialysis patients with native arteriovenous fistula and evaluated the impact of statin treatment on vascular access patency.

METHODS

A retrospective cohort study of 268 consecutive patients who newly started hemodialysis due to diabetic nephropathy between January 2011 and December 2013 at Japan Community Health Care Organization Sendai Hospital was performed and the patients were followed for two years. The primary outcome was vascular access dysfunction. Effect of statin treatment was examined using Kaplan Meier analysis and Cox proportional hazard, after adjusting for covariates.

RESULTS

The mean follow-up period was 426.7 days, and 117 (52.2%) patients developed vascular access dysfunction. The two-year patency rate was 55.0% among statin users and 36.1% in non-users. Vascular access survival period was significantly longer among statin users (log-rank test, p = 0.004). In multivariable analysis, statin treatment is significantly associated with better vascular access outcomes, in which the hazard ratio was 0.71 (95% CI, 0.52 to 0.97; p = 0.028) in the unadjusted model and 0.63 (95% CI, 0.45 to 0.88; p = 0.007) after adjustment for covariates.

CONCLUSIONS

Statin treatment could be associated with improved vascular access dysfunction among diabetic hemodialysis patients.

Arteriovenous fistula maturation in patients with permanent access created prior to or after hemodialysis initiation

INTRODUCTION

Multiple factors and comorbidities have been implicated in the ability of arteriovenous fistulas (AVF) to mature, including vessel anatomy, advanced age, and the presence of coronary artery disease or peripheral vascular disease. However, little is known about the role of uremia on AVF primary failure. In this study, we attempt to evaluate the effect of uremia on AVF maturation by comparing AVF outcomes between pre-dialysis chronic kidney disease (CKD) stage five patients and those who had their AVF created after hemodialysis (HD) initiation.

METHODS

We included 612 patients who underwent AVF creation between 2003 and 2015 at the University of Miami Hospital and Jackson Memorial Hospital. Effects of uremia on primary failure were evaluated using univariate statistical comparisons and multivariate logistic regression analyses.

RESULTS

Primary failure occurred in 28.1% and 26.3% of patients with an AVF created prior to or after HD initiation, respectively (p = 0.73). The time of HD initiation was not associated with AVF maturation in multivariate logistic regression analysis (p = 0.57). In addition, pre-operative blood urea nitrogen (p = 0.78), estimated glomerular filtration rate (p = 0.66), and serum creatinine levels (p = 0.14) were not associated with AVF primary failure in pre-dialysis patients.

CONCLUSIONS

Our results show that clearance of uremia with regular HD treatments prior to AVF creation does not improve the frequency of vascular access maturation.

The molecular mechanisms of hemodialysis vascular access failure

The arteriovenous fistula has been used for more than 50 years to provide vascular access for patients undergoing hemodialysis. More than 1.5 million patients worldwide have end stage renal disease and this population will continue to grow. The arteriovenous fistula is the preferred vascular access for patients, but its patency rate at 1 year is only 60%. The majority of arteriovenous fistulas fail because of intimal hyperplasia. In recent years, there have been many studies investigating the molecular mechanisms responsible for intimal hyperplasia and subsequent thrombosis. These studies have identified common pathways including inflammation, uremia, hypoxia, sheer stress, and increased thrombogenicity. These cellular mechanisms lead to increased proliferation, migration, and eventually stenosis. These pathways work synergistically through shared molecular messengers. In this review, we will examine the literature concerning the molecular basis of hemodialysis vascular access malfunction.

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.

Distinct impact of three different statins on arteriovenous fistula outcomes: a retrospective analysis

PURPOSE

Whether statins improve arteriovenous fistula (AVF) outcomes is still a matter of debate. Taking into consideration the existing physicochemical differences between individual drugs, this study evaluates the impact of three different statins (atorvastatin, rosuvastatin and simvastatin) on one-stage and two-stage AVF outcomes.

METHODS

Using a retrospective cohort of 535 patients, we analyzed the effects of each statin on primary failure and primary patency using multivariate logistic regressions and Cox proportional hazard models.

RESULTS

Out of the three statins analyzed, only atorvastatin improved the overall primary failure of AVF (odds ratio [OR] = 0.18, p = 0.005). Comparisons between the two AVF types demonstrated that this effect was due to a prominent reduction in primary failure of one-stage (OR = 0.03; p = 0.005), but not two-stage fistulas (OR = 0.43; p = 0.25). In contrast, primary patency of two-stage (hazards ratio [HR] = 0.51; p = 0.024), but not one-stage fistulas (HR = 0.98; p = 0.95), was improved by all statins as a group, but not by individual drugs.

CONCLUSIONS

Our results suggest that the potential benefit of statins on AVF outcomes is a drug-specific and not a class effect, and that such effect is also influenced by the type of fistula.

Dialysis Arteriovenous Fistula Failure and Angioplasty: Intimal Hyperplasia and Other Causes of Access Failure

The arteriovenous fistula (AVF) is the preferred hemodialysis access type because it has better patency rates and fewer complications than other access types. However, primary failure remains a common problem impeding AVF maturation and adding to patients' morbidity and mortality. Juxta-anastomotic (or inflow) stenosis is the most common reason leading to primary failure, and percutaneous transluminal angioplasty continues to be the gold-standard treatment with excellent success rates. Intimal hyperplasia (IH) has been traditionally blamed as the main pathophysiologic culprit, but new evidence raises doubts regarding the contribution of IH alone to primary failure. We report a 64-year-old man with a 2-stage brachiobasilic AVF that was complicated by failure 4 months after creation. An angiogram showed multiple juxta-anastomotic and midfistula stenotic lesions. Percutaneous transluminal angioplasty was successful in assisting maturation and subsequently cannulating the AVF for hemodialysis treatment. We failed to identify the underlying cause of stenosis because biopsy specimens from fistula tissue obtained at the time of transposition revealed no occlusive IH. This case emphasizes the need for additional research on factors contributing to AVF failure besides IH and highlights the need for more therapeutic options to reduce AVF failure rate.

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.

Heparin-bonded expanded polytetrafluorethylene grafts in hemodialysis access

When options for autologous arteriovenous (AV) fistulas have been fully exhausted, AV grafts continue to play an important role in access creation for hemodialysis, offering long-term hemodialysis access that is a better alternative to central vein catheters. The drawbacks of AV grafts are their poor patency, infection and higher cost. Their main advantages are that they are widely available, are easy to create, and mature early. In the context of the "Fistula First" initiative, many patients with low quality veins suffer from fistula failure and non-maturation resulting in prolonged catheter days that would otherwise be prevented by initial creation of an AV graft. Endeavors to improve graft patency include administration of pharmacological agents, changing graft configuration, altering graft biology, and altering the graft surface. In this review, the current status of heparin-bonded AV grafts for hemodialysis is discussed.

Statins Improve Long Term Patency of Arteriovenous Fistula for Hemodialysis

The protective effects of statins against stenosis for permanent hemodialysis access have been repeatedly demonstrated in animal studies, but remain controversial in human studies. This study aims to evaluate the association between statin use and permanent hemodialysis access patency using a nationwide hemodialysis cohort. A total of 9862 pairs of statin users and non-users, matched by age and gender, were selected for investigation from 75404 new hemodialysis patients during 2000-2008. The effect of statins on permanent hemodialysis access patency was evaluated using Cox proportional hazards models. Compared with non-users, statin users had an overall 18% risk reduction in the composite endpoint in which angioplasty and recreation were combined (adjusted hazard ratio = 0.82 [95%CI, 0.78-0.87]) and 21% in recreation of permanent hemodialysis access (adjusted hazard ratio = 0.79 [95%CI, 0.69-0.80]). Specifically, the protective effect was found for arteriovenous fistula (adjusted hazard ratio = 0.78[95% CI, 0.73-0.82] for composite endpoint and 0.74 [95% CI, 0.69-0.80] for vascular recreation), but not for arteriovenous grafts (adjusted hazard ratio = 1.10 [95% CI, 0.98-1.24] and 0.94 [95% CI, 0.83-1.07]). Statins possess a protective effect for arteriovenous fistula against the recreation of permanent hemodialysis access. The results provide a pharmaco-epidemiologic link between basic research and clinical evidence.

Risk of arteriovenous fistula failure associated with hypnotic use in hemodialysis patients: a nested case-control study

PURPOSE

Hypnotic use might cause altered inflammatory processes, which have been suggested as being related to the mechanisms of arteriovenous fistula (AVF) failure. Therefore, we examined the association between the risk of AVF failure and hypnotic use in patients receiving hemodialysis (HD).

METHODS

A nested case-control study was conducted using data from the National Health Insurance Research Database of Taiwan. From 34 165 HD patients, 3676 patients receiving percutaneous transluminal angioplasty or surgical thrombectomy for AVF failure were matched to 14 704 control patients according to sex, age (±1 year), and the year of initial HD therapy. The risk of AVF failure was estimated based on conditional logistic regression after adjustment for the timing of AVF creation, HD frequency, comorbidities, and prescribed medications. Hypnotic use was measured prior to the date of AVF failure of case patients and the date of pseudo-AVF failure of controls.

RESULTS

Compared with matched controls, case patients were more likely to be exposed to hypnotics 30 days or an average daily defined dose > 0.5 within 90 days before the date of AVF failure, with an adjusted odds ratio of 1.21 (95% confidence interval [CI]: 1.09-1.35, p < 0.001) and 1.36 (95%CI: 1.13-1.63, p = 0.001), respectively. Risk of AVF failure associated with hypnotic use was also observed among HD patients who were male, were younger than 65 years, had hypertension, and did not use statins.

CONCLUSIONS

Hypnotic use among HD patients was associated with an increased risk of AVF failure. Copyright © 2016 John Wiley & Sons, Ltd.

Endothelial cell activation by hemodynamic shear stress derived from arteriovenous fistula for hemodialysis access

Intimal hyperplasia (IH) is the first cause of failure of an arteriovenous fistula (AVF). The aim of the present study was to investigate the effects on endothelial cells (ECs) of shear stress waveforms derived from AVF areas prone to develop IH. We used a cone-and-plate device to obtain real-time control of shear stress acting on EC cultures. We exposed human umbilical vein ECs for 48 h to different shear stimulations calculated in a side-to-end AVF model. Pulsatile unidirectional flow, representative of low-risk stenosis areas, induced alignment of ECs and actin fiber orientation with flow. Shear stress patterns of reciprocating flow, derived from high-risk stenosis areas, did not affect EC shape or cytoskeleton organization, which remained similar to static cultures. We also evaluated flow-induced EC expression of genes known to be involved in cytoskeletal remodeling and expression of cell adhesion molecules. Unidirectional flow induced a significant increase in Kruppel-like factor 2 mRNA expression, whereas it significantly reduced phospholipase D1, α4-integrin, and Ras p21 protein activator 1 mRNA expression. Reciprocating flow did not increase Kruppel-like factor 2 mRNA expression compared with static controls but significantly increased mRNA expression of phospholipase D1, α4-integrin, and Ras p21 protein activator 1. Reciprocating flow selectively increased monocyte chemoattractant protein-1 and IL-8 production. Furthermore, culture medium conditioned by ECs exposed to reciprocating flows selectively increased smooth muscle cell proliferation compared with unidirectional flow. Our results indicate that protective vascular effects induced in ECs by unidirectional pulsatile flow are not induced by reciprocating shear forces, suggesting a mechanism by which oscillating flow conditions may induce the development of IH in AVF and vascular access dysfunction.

Upper Limb Grafts for Hemodialysis Access

Arteriovenous (AV) grafts are required for hemodialysis access when options for native fistulas have been fully exhausted, where they continue to play an important role in hemodialysis patients, offering a better alternative to central vein catheters. When planning autogenous accesses using Doppler ultrasound, adequate arterial inflow and venous outflow must be consciously preserved for future access creation with grafts. Efforts to improve graft patency include changing graft configuration, graft biology and hemodynamics. Industry offers early cannulation grafts to reduce central catheter use and a bioengineered graft is undergoing clinical studies. Although the outcome of AV grafts is inferior to fistulas, grafts can provide long-term hemodialysis access that is a better alternative to central venous catheters. AV grafts have significant drawbacks, mainly poor patency, infection and cost but also have some advantages: early maturation, ease of creation and needling and widespread availability. The outcome of AV graft surgery is variable from center to center. The primary patency rate for AV grafts is 58% at 6 months and the secondary patency rate is 76% at 6 months and 55% at 18 months. There are centers of excellence that report a 1 year secondary patency rate of up to 91%. In this review of the use of AV grafts for hemodialysis access in the upper extremities, technical issues involved in planning the access and performing the surgery in its different configurations are discussed and the role of surveillance and maintenance with their attendant surgical and radiological interventions is described.

The effect of lowering LDL cholesterol on vascular access patency: post hoc analysis of the Study of Heart and Renal Protection

BACKGROUND AND OBJECTIVES

Reducing LDL cholesterol (LDL-C) with statin-based therapy reduces the risk of major atherosclerotic events among patients with CKD, including dialysis patients, but the effect of lowering LDL-C on vascular access patency is unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Study of Heart and Renal Protection (SHARP) randomized patients with CKD to 20 mg simvastatin plus 10 mg ezetimibe daily versus matching placebo. This study aimed to explore the effects of treatment on vascular access occlusive events, defined as any access revision procedure, access thrombosis, removal of an old dialysis access, or formation of new permanent dialysis access.

RESULTS

Among 2353 SHARP participants who had functioning vascular access at randomization, allocation to simvastatin plus ezetimibe resulted in a 13% proportional reduction in vascular access occlusive events (355 [29.7%] for simvastatin/ezetimibe versus 388 [33.5%] for placebo; risk ratio [RR], 0.87; 95% confidence interval [95% CI], 0.75 to 1.00; P=0.05). There was no evidence that the effects of treatment differed for any of the separate components of this outcome. To test the hypothesis raised by SHARP, comparable analyses were performed using the AURORA (A Study to Evaluate the Use of Rosuvastatin in Subjects on Regular Hemodialysis: An Assessment of Survival and Cardiovascular Events) trial cohort. AURORA did not provide independent confirmation (vascular access occlusive events: 352 [28.9%] for rosuvastatin versus 337 [27.6%] for placebo; RR, 1.06, 95% CI, 0.91 to 1.23; P=0.44). After combining the two trials, the overall effect of reducing LDL-C with a statin-based regimen on vascular access occlusive events was not statistically significant (707 [29.3%] with any LDL-C-lowering therapy versus 725 [30.5%] with placebo; RR, 0.95, 95% CI, 0.85 to 1.05; P=0.29).

CONCLUSIONS

Exploratory analyses from SHARP suggest that lowering LDL-C with statin-based therapy may improve vascular access patency, but there was no evidence of benefit in AURORA. Taken together, the available evidence suggests that any benefits of lowering LDL-C on vascular access patency are likely to be modest.

Simvastatin reduces venous stenosis formation in a murine hemodialysis vascular access model

Venous neointimal hyperplasia (VNH) is responsible for hemodialysis vascular access malfunction. Here we tested whether VNH formation occurs, in part, due to vascular endothelial growth factor-A (VEGF-A) and matrix metalloproteinase (MMP)-9 gene expression causing adventitial fibroblast transdifferentiation to myofibroblasts (α-SMA-positive cells). These cells have increased proliferative and migratory capacity leading to VNH formation. Simvastatin was used to decrease VEGF-A and MMP-9 gene expression in our murine arteriovenous fistula model created by connecting the right carotid artery to the ipsilateral jugular vein. Compared to fistulae of vehicle-treated mice, the fistulae of simvastatin-treated mice had the expected decrease in VEGF-A and MMP-9 but also showed a significant reduction in MMP-2 expression with a significant decrease in VNH and a significant increase in the mean lumen vessel area. There was an increase in terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, and decreases in α-SMA density, cell proliferation, and HIF-1α and hypoxyprobe staining. This latter result prompted us to determine the effect of simvastatin on fibroblasts subjected to hypoxia in vitro. Simvastatin-treated fibroblasts had a significant decrease in myofibroblast production along with decreased cellular proliferation, migration, and MMP-9 activity but increased caspase 3 activity suggesting increased apoptosis. Thus, simvastatin results in a significant reduction in VNH, with increase in mean lumen vessel area by decreasing VEGF-A/MMP-9 pathway activity.

Vascular Access versus the Effect of Statins on Inflammation and Fibrinolysis in Renal Dialysis Patients

Purpose

The aim of this work was to assess the effect of statin therapy on inflammatory and fibrinolytic/endothelial (dys)function markers in end-stage renal disease (ESRD) patients under hemodialysis (HD), according to the type of vascular access.

Methods

This transversal study includes 191 ESRD patients under regular HD, divided into four groups according to vascular access and statin therapy: 87 patients with arteriovenous fistula (AVF) and no statins (AVF-NS), 61 with AVF and statins (AVF-S), 27 with central venous dialysis catheter (CVC) and no statins (CVC-NS) and 16 with CVC and statins (CVC-S). The basic lipid profile and fibrinolytic/endothelial cell function markers were assessed.

Results

Patients with CVC presented significantly higher levels of D-dimers compared with AVF groups. CVC-NS patients also presented the highest IL-6 values, which were significantly higher than those presented by CVC-S patients. AVF-S patients presented significantly higher t-PA and PAI-1 values and lower adiponectin levels compared with AVF-NS.

Conclusions

Our results demonstrate that patients with CVC, particularly those not under statin therapy, present a higher production and turnover of fibrin. We also found that statin therapy decreases inflammation in CVC patients but is associated with a reduction of adiponectin and increased endothelial function marker levels in AVF patients.

The effect of statin therapy on the formation of arteriovenous fistula stenoses and the rate of reoccurrence of previously treated stenoses

Statins reduce inflammation in end-stage renal disease patients and improve endothelial function beyond cholesterol lowering. Despite this, statins do not improve the maturation rate, primary patency rate, and the cumulative survival of arteriovenous fistulas (AVFs). It is unknown if statins decrease the number of stenoses developing in AVFs or prolong the intervals between angioplasties needed to treat recurring stenoses. We conducted a retrospective chart review of our 265 active dialysis patients. The statin group was significantly more likely to be diabetic (64% vs. 43.6%) and treated with aspirin (64% vs. 40%) when compared to those not treated with statins (P=0.04 and 0.01). The mean time to first intervention (primary patency) was 16.5 months in statin users and 15.8 months in the nonstatin group (P=0.49) with standard deviations of ± 18.5 and 16.6 months, respectively. Statin use was not associated with a significant decrease in the number of stenoses diagnosed (P=0.28). The mean time between recurrent stenoses' angioplasties was 8.9 months in statin users and 7.3 months in the nonstatin patients (P=0.25). Aspirin users were more likely to have a decreased primary patency (rate ratio=1.65, P=0.03) compared with nonaspirin users. Patients who were prescribed aspirin developed 1.6 (P 0.01) times more stenoses than those not treated with aspirin. We report for the first time that statin therapy does not decrease the number of stenotic lesions developing in the AVF or prolong the interval between procedures required to treat recurrent stenoses.

Statin therapy and hemodialysis vascular access--were we bringing a knife to a gunfight and were hoping to win?

Vascular access dysfunction is a major contributor to end stage renal disease patient morbidity, and the cost of maintaining it is staggering. Any intervention able to improve the vascular access maturation rate and/or patency would be significant progress. Based on the anti-inflammatory and vascular beneficial effects demonstrated in non-end stage renal disease patients, we were hoping that statin use might provide the much needed improvement in the hemodialysis vascular access outcome. The reality proved disappointing. The statins failed to improve every aspect of hemodialysis vascular access studied. The present editorial discusses the current data regarding the effect of statins on vascular access and attempts to explain their lack of success.