Plasma ADMA predicts restenosis of arteriovenous fistula

Outcome and Risk Factors of Restenosis Post Percutaneous Transluminal Angioplasty at Juxta-Anastomotic of Wrist Autogenous Radial-Cephalic Arteriovenous Fistulas: A Retrospective Cohort Study

BACKGROUND

This retrospective cohort study was to determine the factors related to restenosis post percutaneous transluminal angioplasty (PTA) at juxta-anastomotic of wrist radial-cephalic arteriovenous fistulas (RC-AVFs).

METHODS

We conducted a retrospective study of patients who underwent their first PTA for juxta-anastomotic stenosis at RC-AVF from January 1, 2016, to December 31, 2020. Patient and stenotic lesion characteristics and PTA procedure factors were included in the analysis. The primary and assisted primary patency post PTA of RC-AVFs were evaluated using the Kaplan-Meier analysis and log-rank test. A Cox proportional hazard model was used to identify factors associated with restenosis post PTA. The receiver operating characteristic (ROC) curve was employed to evaluate the predictive value of the risk factors for restenosis post PTA.

RESULTS

A total of 65 patients with a mean age of 59.09 ± 14.94 years were enrolled in the study. The mean RC-AVF age was 9.2 (4.9, 35.05) months, and the median time of intervention for stenosis was 10.8 (4.05, 41.35) months after AVF creation. The primary patency rates following the first PTA at 3, 6, 12, and 24 months were 93.9, 84.6, 63.1, and 55.4%, respectively. The assisted primary patency rates at 3, 6, 12, and 24 months were 95.4, 90.8, 87.7, and 84.6%, respectively. Cox proportional hazard regression analysis revealed the maximum balloon diameter >5 mm had a lower postoperative restenosis rate compared with the maximum balloon diameter ≤5 mm (hazard ratio = 0.422; 95% confidence interval [CI]: 0.201-0.884; P = 0.022). ROC curve analysis showed that the area under the curve of the maximum balloon diameter during PTA was 0.624 (95% CI, 0.486-0.762). The best critical value for the maximum balloon diameter was 6 mm, the sensitivity was 64.5%, and the specificity was 61.8%.

CONCLUSIONS

For the first PTA at juxta-anastomotic of wrist RC-AVFs without thrombosis and complete occlusion, the use of a balloon with a maximum diameter of ≤5 mm is a risk factor to the occurrence of restenosis within 12 months post PTA. The result may help in tailoring surveillance programs in patients with RC-AVF stenosis.

The association of long-term blood pressure variability with hemodialysis access thrombosis

Background

Blood pressure variability (BPV) is an important risk factor for cardiovascular events in hemodialysis patients. We sought to determine the impact of BPV on hemodialysis access thrombosis.

Methods

We enrolled 1,011 prevalent hemodialysis patients from 12 hemodialysis centers since January 2018 and followed them until December 2020. Predialysis blood pressure (BP) was assessed at 12-week intervals. The coefficient of variation derived from 36 consecutive BP measurements was used as the metric for variability. The primary outcome was incident hemodialysis access thrombosis. Linear regression models were used to assess factors associated with BPV at baseline. Kaplan-Meier curves of the time until vascular access events were drawn and log-rank tests were calculated. Cox proportional hazards models were performed to assess the association of BPV with incident vascular access events.

Results

The average coefficient of variance for systolic BPV was 10.9%. BPV was associated with age, body mass index, mean BP, diabetes, coronary and peripheral artery disease, history of access dysfunction, graft access, intradialytic hypotension, and use of antihypertensive medications. There were 194 access thrombosis events and 451 access stenosis events during a median follow-up period of 30 months. After adjustment of potential confounding factors, BPV was associated with increased risk of access thrombosis [hazard ratio = 1.27, 95% confidence interval (CI), 1.18–1.44, per 1 standard deviation increase in BPV]. The patients in the highest BPV quartile had 2.45 times the risk of thrombosis (CI, 1.62–3.70). The association was independent of average BP, intradialytic hypotension, and comorbidities. Similar trends of association were found in the subgroups analyzed. Comparative analysis using a time-varying variable model and different metrics of BPV showed consistent results.

Conclusion

Our findings underscored the impact of BP fluctuation on vascular access thrombosis.

Far-Infrared Therapy Improves Arteriovenous Fistula Patency and Decreases Plasma Asymmetric Dimethylarginine in Patients with Advanced Diabetic Kidney Disease: A Prospective Randomized Controlled Trial

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and plays a significant role in the pathogenesis of arteriovenous fistula (AVF) dysfunction. The aim of this study is to evaluate the effect of far-infrared (FIR) therapy on the maturation and patency of newly-created AVFs in patients with advanced diabetic kidney disease (DKD) as well as the concurrent change in plasma ADMA. The study enrolled 144 participants with advanced DKD where 101 patients were randomly allocated to the FIR therapy group (N = 50) and control group (N = 51). Patients receiving FIR therapy had a decreased AVF failure rate within 12 months (16% versus 35.3%; p = 0.027); decreased incremental change of ADMA concentration at the 3rd and 12th month; increased AVF blood flow at the 1st, 3rd, and 12th month; increased 3-month physiologic maturation rate (88% versus 68.6%; p = 0.034); increased 1-year unassisted AVF patency rate (84% versus 64.7%; p = 0.017); and increased clinical AVF maturation rate within 12 months (84% versus 62.7%; p = 0.029) compared to the control group. The study demonstrates that FIR therapy can reduce the incremental changes in plasma ADMA concentration, which may be associated with the improvement of AVF prognosis in patients with advanced DKD.

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.

The Role of Oxidative Stress Markers in Predicting Acute Thrombotic Occlusion of Haemodialysis Vascular Access and Progressive Stenotic Dysfunction Demanding Angioplasty

Haemodialysis vascular access (VA) dysfunction is a major cause of morbidity in haemodialysis (HD) patients. Primary venous outflow occlusion and restenosis after percutaneous transluminal angioplasty (PTA) are two major obstacles for the long-term use of dialysis VA. It remains unclear whether oxidative stress markers can be used as predictors for thrombotic occlusion of VA and progressive stenosis dysfunction demanding PTA. All routine HD patients at one teaching hospital participated in this study including ankle-brachial index (ABI) examinations and serum oxidative stress markers. The serum oxidative stress markers (high-sensitivity C-reactive protein (hs-CRP), matrix metalloproteinase-2 (MMP-2), MMP-9, homocysteine, asymmetrical dimethylarginine (ADMA), nitrate oxidase (NO), tumour necrosis factor-α (TNF-α), monocyte chemotactic protein 1 (MCP-1), interleukin-1β (IL-1β), and transforming growth factor-β (TGF-β)) were measured using immunosorbent assays in 159 HD patients (83 men and 76 women; mean age: 65 ± 12 years). The participants met the following criteria: (1) received regular HD treatment for at least 6 months, without clinical evidence of acute or chronic inflammation, recent myocardial infarction, unstable angina or circulatory congestion; and (2) received an arteriovenous fistula (AVF)/arteriovenous graft (AVG: polytetrafluoroethylene, PTFE) as the current VA for more than 6 months, without interventions within the last 6 months. All the participants were followed up clinically for up to 12 months to estimate the amount of primary thrombotic occlusion and VA dysfunction demanding PTA. During the 12-month observation, 24 patients (15.1%) had primary thrombotic occlusion of VAs. Another 24 patients (15.1%) required PTA because of clinical dysfunction of access. Additionally, during the follow-up period, restenosis occurred in 12 patients (50% of 24 patients). The access types of arteriovenous grafts (AVGs) and a diagnosis of peripheral arterial occlusive disease (PAOD) were two strong predictors for acute thrombotic events of VA (hazard ratio (HR): 16.93 vs. 2.35; p < 0.001 vs. 0.047). Comparing dysfunctional with non-dysfunctional VAs, up to 27.7% of patients with high levels of ADMA (>0.6207 μM, N = 65) received required PTA compared with 4.4% of those with low levels (≤0.6207 μM; N = 90; p < 0.001). In multivariate analysis, the plasma baseline levels of ADMA independently conferred nearly 4.55 times the risk of primary stenotic dysfunction of HD VA (HR: 4.55; 95% confidence interval: 1.20 to 17.26; p = 0.026). In conclusion, our findings suggest the role of ADMA in the development of symptomatic VA dysfunction. Additionally, PAOD severity can be used in clinical practice to predict whether acute thrombotic occlusion of VA will easily occur in HD patients.

Predictors associated with early and late restenosis of arteriovenous fistulas and grafts after percutaneous transluminal angiography

BACKGROUND

The objective of this study was to assess postintervention patency and analyze the predictive factors associated with early and late restenosis after intervention in hemodialysis arteriovenous fistulas (AVF) and arteriovenous grafts (AVG).

METHODS

This study retrospectively analyzed 284 hemodialysis patients who underwent percutaneous transluminal angioplasty (PTA) due to AVF and AVG stenosis. A total of 350 PTA procedures were performed. Clinical, anatomical, biochemical, and technical variables were analyzed. Using univariate and multivariate analyses, we assessed the postintervention patency of PTA by follow-up, and identified the predictive factors taking into account competing risks.

RESULTS

Postintervention patency rates at 3, 6, 12, and 24 months were 86.5%, 66.4%, 42.6%, and 29.8%, respectively, with a median patency duration of 11±0.71 months. Kaplan-Meier analysis showed that the patency rate of the AVF group (n=271) was dramatically higher than the AVG group (n=79) at 3, 6, and 12 months after PTA, respectively (88.9% vs. 78.5%, 69.0% vs. 57.4%, 48.8% vs. 20.0%, P<0.01). Cox survival analysis revealed that the factors associated with postintervention patency of AVF included age of fistulas, serum albumin (ALB) levels, location of stenoses, lesion length longer than 2 cm, multiple stenoses, and maximal pressure of dilatation lower than 16 atm. In addition, factors related to postintervention patency of AVG included the presence of diabetes and hypertension, and serum ALB.

CONCLUSIONS

This study demonstrated that the risk factors associated with postintervention patency of AVF included age of fistulas, lower levels of serum ALB, location of stenoses, lesion length longer than 2 cm, multiple stenoses, and maximal pressure of dilatation lower than 16 atm. In addition, risk factors related to postintervention patency of AVG included the presence of diabetes and lower levels of serum ALB, while the presence of hypertension was found to be a protective factor for reducing patency loss of AVG. Among all these factors, serum ALB and multiple stenoses tended to predict early restenosis, while pressure of dilatation tended to predict late restenosis.

Analysis of factors for post–percutaneous transluminal angioplasty primary patency rate in hemodialysis vascular access

Background:

Although percutaneous transluminal angioplasty has been established as a first-line therapy for access failure in dialysis, there are few reports on primary patency after percutaneous transluminal angioplasty. We investigated factors associated with primary patency following the first percutaneous transluminal angioplasty performed after vascular access construction in patients with arteriovenous fistula, including blood flow volume before and after percutaneous transluminal angioplasty and previously reported factors.

Methods:

We used medical records at six dialysis centers to retrospectively identify and analyze prognostic factors for primary patency after percutaneous transluminal angioplasty in 159 patients with arteriovenous fistula who underwent initial percutaneous transluminal angioplasty after vascular access construction.

Results:

Multivariate analysis with the Cox proportional hazard model showed that primary patency after percutaneous transluminal angioplasty in patients with arteriovenous fistula was significantly associated with lesion length (hazard ratio, 1.76; 95% confidence interval, 1.01–3.07; P = 0.045), and blood flow volume after percutaneous transluminal angioplasty (hazard ratio, 0.71; 95% confidence interval, 0.60–0.84; P < 0.001). When blood flow volume after percutaneous transluminal angioplasty was classified into three categories, risks of outcome events defining the end of primary patency after percutaneous transluminal angioplasty were significantly lower for 400–630 mL/min (hazard ratio, 0.38; 95% confidence interval, 0.21–0.68; P = 0.001) and >630 mL/min (hazard ratio, 0.16; 95% confidence interval, 0.06–0.40; P < 0.001) compared with <400 mL/min.

Conclusion:

Our study showed that blood flow volume after percutaneous transluminal angioplasty is an important prognostic factor for primary patency after percutaneous transluminal angioplasty in patients with arteriovenous fistula.

Outcomes after Percutaneous Angioplasty of Arteriovenous Fistulas and Grafts in African American Patients

Purpose

Arteriovenous fistulas and grafts, necessary for hemodialysis, may develop stenoses due to neointimal hyperplasia, which often require percutaneous transluminal angioplasty. Patient and lesion characteristics were evaluated prior to angioplasty and were correlated with 1- and 6-month outcomes.

Materials and Methods

This was an observational study of African American hemodialysis patients who presented for angioplasty of a dysfunctional fistula or graft. Clinical outcomes were ascertained from dialysis facilities 1 month and 6 months after angioplasty. One-month clinical success was defined as dialyzer blood flows of 450 mL/min without complications or interval shunt thrombosis, interventions, or loss of access, which was rarely achieved at 6 months. Logistic regression models were used to evaluate associations of clinical variables with outcomes.

Results

There were 150 stenoses treated during 99 procedures performed on 82 patients. The clinical success rate at one month was 67% with no complications as a result of the percutaneous transluminal angioplasty. Success at 1 month was positively associated with use of aspirin ( P = .005) and with referral for high venous pressures ( P = .004). Six-month data were available for 81 procedures, with 45.7% requiring repeat angioplasty and 12.3% suffering major complications (thrombectomy, revision surgery, or access abandonment). Major complications were seen predominantly in patients who were not receiving aspirin.

Conclusions

Aspirin use and high venous pressure were associated with 1-month clinical success and fewer major complications at 6 months. Future work should investigate biologic mechanisms of action of aspirin and long-term effects of use to maintain vascular access.

Temporal distribution and biological determinants of thrombotic events after interventions for dialysis vascular access

Endovascular therapy is the principal therapy for haemodialysis vascular access dysfunction. Nonetheless, the incidence and determinants of post-intervention thrombotic events are unclear. This prospective cohort study evaluated the incidence and timing of thrombotic events after endovascular therapy and analysed the clinical, angiographic, and biological determinants of thrombosis. Of the 236 patients enrolled, 91 experienced post-intervention thrombotic events within 1 year. The 1-year thrombosis-free patency was 28% for thrombosed accesses, 53% for non-thrombosed grafts, and 78% for non-thrombosed fistulas. Forty-one of the 91 thrombotic events (45%) occurred within 3 months post-intervention. In the univariate analysis, early thrombosis was associated with longer haemodialysis duration (hazard ratio [HR], 1.01; 95% confidence interval [CI], 1.01–1.02), graft access (HR, 7.69; 95% CI, 3.33–20.0), multiple stenoses (HR, 2.69; 95% CI, 1.36–5.37), and high indoxyl sulphate (IS) levels (HR, 1.55; 95% CI, 1.32–1.82). Late thrombosis was associated with diabetes (HR, 1.89; 95% CI, 1.01–3.57), cardiovascular disease (HR, 2.38; 95% CI, 1.27–4.54), and endothelial progenitor cell counts (HR, 0.97; 95% CI, 0.93–0.99). After multivariate adjustment, high IS was the major predisposing factor for early post-intervention thrombosis (HR, 1.41; 95% CI, 1.18–1.69). Our findings suggest that measures to decrease IS could target the most critical period of thrombosis.

Factors associated with outcome after successful radiological intervention in arteriovenous fistulas: A retrospective cohort

Introduction:

Arteriovenous fistulas are the best form of vascular access for haemodialysis. A radiological balloon angioplasty is the standard treatment for a clinically relevant stenosis, but the recurrence rate is high. Data on factors associated with recurrence are limited.

Methods:

A single centre, retrospective analysis was performed for 124 consecutive patients who had successful interventions for dysfunctional arteriovenous fistulae, to examine factors associated with post-intervention patency. Follow-up was at least 1 year for all patients. Variables associated with primary and cumulative patency were pre-specified and assessed using both un-adjusted (univariate) and adjusted Cox proportional hazards models. Analysis was repeated for a subgroup of 80 patients with a single lesion only in order to examine the potential effects of stenotic lesion characteristics on patency.

Results:

Factors found to have a significant association with poorer outcomes (less time to loss of patency) included thrombosis at the time of intervention and a history of previous intervention. Fistula age (log days) was significantly associated with better outcomes (greater time to loss of patency). Non-white ethnicity, lesion length, and patient age were also significantly associated with accelerated loss of patency.

Discussion:

The factors we have identified as linked to poor outcome may help to identify patients in whom a balloon angioplasty is unlikely to provide a durable outcome. This may prompt exploring alternative treatment or dialysis options at an early stage.

Deterioration of Deceleration Capacity of Heart Rate is Associated with Left Ventricular Hypertrophy in End-Stage Renal Disease Population

BACKGROUND

Left ventricular hypertrophy (LVH) is prevalent in patients with end-stage renal disease (ESRD), and may be secondary to arterial stiffness and volume overload. It is unclear whether LVH is caused by autonomic nerve dysregulation (AND), a frequent condition in patients with ESRD that is characterized by sympathetic hyperactivity and vagal withdrawal. We hypothesized that AND estimated by heart rate variability (HRV) may be associated with LVH in patients with ESRD.

METHODS

We prospectively enrolled patients with ESRD undergoing hemodialysis. Cardiac function and LVH were assessed using echocardiography according to the recommendations of the American Society of Echocardiography. Holter recordings were used to quantify HRV and deceleration capacity (DC). Dataon comorbidities and medications, and serum markers were obtained. Logistic regression analysis was performed.

RESULTS

Among the 281 included patients, 63% had LVH. The patients with LVH were older, had more comorbidities and advanced diastolic dysfunction than those without LVH. The root mean square of successive differences (rMSSD) (9.10 ± 5.44 versus 13.25 ± 8.61; p = 0.004) and DC (2.08 ± 1.90 versus 3.89 ± 1.45; p = 0.021) were lower in the patients with LVH than that in those without LVH. Multivariate regression analysis showed that hypertension, asymmetrical dimethylarginine (ADMA), advanced diastolic dysfunction grade, rMSSD, and DC were independently associated with LVH. Among these variables, DC and ADMA showed the highest diagnostic value for LVH with areas under curves of 0.701 and 0.751, respectively.

CONCLUSIONS

AND is independently associated with LVH in patients with ESRD.

Asymmetric Dimethylarginine does not Predict Early Access Events in Hemodialysis Patients with Brachiocephalic Fistula Access

Background

Vascular access for hemodialysis is best provided by an arteriovenous fistula (AVF). AVF fail primarily because of neointimal hyperplasia. Asymmetric dimethlyarginine (ADMA) is a naturally occurring analogue of L-arginine, which is elevated in renal failure and impairs endothelial cell function. ADMA inhibits nitric oxide synthetase, leading to impaired nitric oxide production and contributing to the development of neointimal hyperplasia. ADMA was measured at the time of AVF placement to evaluate associations with access failure.

Methods

ADMA was measured at the time of brachiocephalic access placement. Patients were followed for up to 12 months with end-points of access thrombosis or venous stenosis.

Results

Sixty patients with primary brachiocephalic fistulas were included in the study cohort. The median value for ADMA drawn at the time of AVF creation was 3.1 µmol/L. ADMA was not significantly associated with early thrombosis or venous stenosis events (P>0.05).

Conclusion

Preoperative ADMA levels, as a surrogate for endothelial cell dysfunction and predictor of adverse access event (thrombosis or stenosis), were not associated with subsequent access events Future studies that identify markers of endothelial cell dysfunction are warranted.

Factors influencing dialysis arteriovenous graft survival

PURPOSE

Dysfunction and loss of patency of dialysis arteriovenous grafts (AVGs) are serious causes of morbidity in patients on dialysis. Various risk factors associated with shorter AVG patency have been blamed, but the results of the studies were controversial. The aim of this study was to assess if associated diseases, biochemical markers and other parameters associated with atherosclerosis influence patency of AVGs in a large vascular access centre.

METHODS

We conducted a retrospective study that included patients with AVGs patent for at least 3 weeks after creation. We included variables associated with atherosclerosis into the analysis (coronary artery disease, diabetes mellitus, chronic heart failure, arterial hypertension, smoking history and cholesterol and triglyceride levels) and characteristics of the graft (shape, feeding artery).The data was assessed using log-rank (Cox-Mantel) test. The differences were shown using Kaplan-Meier graphs. The observation period was limited to 1000 days after access creation.

RESULTS

Overall, 338 patients were included in the study. Significantly higher risk of access failure was associated with presence of coronary artery disease (p = 0.0035). Higher serum cholesterol levels were associated with longer survival of the graft in 1000 days of surveillance (p = 0.04).

CONCLUSIONS

Coronary artery disease negatively influences the cumulative patency of vascular access. Higher serum cholesterol levels are associated with lower AVG failure risk over a 1000-day period, which probably corresponds to the worse disease status of the patients with lower cholesterol values.

Does pre- and post-angioplasty Doppler ultrasound evaluation help in predicting vascular access outcome?

BACKGROUND

Kidney Disease - Improving Global Outcomes (KDIGO) recommends post-percutaneous transluminal angioplasty (PTA) <30% residual stenosis (RS) and hemodynamic parameters improvement. Primary end point: how post-PTA access blood flow (ABF) improvement predicts vascular access (VA) outcome. Secondary: compare Doppler ultrasound (DU) and angiography diagnostic accuracy; determine how other factors predict outcome.

METHODS

Eighty patients. DU evaluation performed pre- and post-PTA. Several parameters recorded. Secondary patency verified after 6 months.

RESULTS

Initial ABF 537 ± 248 mL/min; final ABF 1013 ± 354 mL/min. Number and location of stenosis was highly correlated between DU and angiography (p<0.001); central vessels mismatching. First semester overall survival was 63%; significantly better for fistulas (76%) than grafts (51.7%), p 0.044. Final RS>30% associated to better survival, p 0.038. Initial ABF<500 mL/min and multiple stenosis did not affect outcome (p>0.05). A >2-fold ABF increase had no significant impact on fistulas (p>0.05) but was significantly associated with worst outcomes in grafts (23.1% vs. 73.5%, p 0.009). Grafts had lower survival (HR 3.3, p 0.034).

CONCLUSIONS

Although less accurate for central lesions, DU has a key role on VA surveillance, allowing a morphologic and hemodynamic assessment. Angioplasty is effective in preserving VA; however, it may increase restenosis due to accelerated neointimal hyperplasia. Current parameters are not useful. Trials addressing this issue are needed.

Future research directions to improve fistula maturation and reduce access failure

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

A Systematic Review and Meta-Analysis of Circulating Biomarkers Associated with Failure of Arteriovenous Fistulae for Haemodialysis

BACKGROUND

Arteriovenous fistula (AVF) failure is a significant cause of morbidity and expense in patients on maintenance haemodialysis (HD). Circulating biomarkers could be valuable in detecting patients at risk of AVF failure and may identify targets to improve AVF outcome. Currently there is little consensus on the relationship between circulating biomarkers and AVF failure. The aim of this systematic review was to identify circulating biomarkers associated with AVF failure.

METHODS

Studies evaluating the association between circulating biomarkers and the presence or risk of AVF failure were systematically identified from the MEDLINE, EMBASE and Cochrane Library databases. No restrictions on the type of study were imposed. Concentrations of circulating biomarkers of routine HD patients with and without AVF failure were recorded and meta-analyses were performed on biomarkers that were assessed in three or more studies with a composite population of at least 100 participants. Biomarker concentrations were synthesized into inverse-variance random-effects models to calculate standardized mean differences (SMD) and 95% confidence intervals (CI).

RESULTS

Thirteen studies comprising a combined population of 1512 participants were included after screening 2835 unique abstracts. These studies collectively investigated 48 biomarkers, predominantly circulating molecules which were assessed as part of routine clinical care. Meta-analysis was performed on twelve eligible biomarkers. No significant association between any of the assessed biomarkers and AVF failure was observed.

CONCLUSION

This paper is the first systematic review of biomarkers associated with AVF failure. Our results suggest that blood markers currently assessed do not identify an at-risk AVF. Further, rigorously designed studies assessing biological plausible biomarkers are needed to clarify whether assessment of circulating markers can be of any clinical value. PROSPERO registration number CRD42016033845.

New Developments in Our Understanding of Neointimal Hyperplasia

The vascular access remains the lifeline for the hemodialysis patient. The most common etiology of vascular access dysfunction is venous stenosis at the vein-artery anastomosis in arteriovenous fistula and at the vein-graft anastomosis in arteriovenous grafts (AVG). This stenotic lesion is typically characterized on histology as aggressive venous neointimal hyperplasia in both arteriovenous fistula and AVG. In recent years, we have advanced our knowledge and understanding of neointimal hyperplasia in vascular access and begun testing several novel therapies. This article will (1) review recent developments in our understanding of the pathophysiology of neointimal hyperplasia development in AVG and fistula failure, (2) discuss atypical factors leading to neointimal hyperplasia development, (3) highlight key novel therapies that have been evaluated in clinical trials, and (4) discuss future opportunities and challenges to improve our understanding of vascular access dysfunction and translate this knowledge into novel and innovative therapies.

Hemodynamic and biologic determinates of arteriovenous fistula outcomes in renal failure patients

The outcome of patients with end-stage renal disease on hemodialysis depends on a functioning vascular access. Although a variety of access options are available, the arteriovenous fistula remains the best vascular access. Unfortunately the success rate of mature fistula use remains poor. The creation of an arteriovenous fistula is followed by altered hemodynamic and biological changes that may result in neointimal hyperplasia and eventual venous stenosis. This review provides an overview of these changes and the needed research to provide a long lasting vascular access and hence improve outcomes for patients with end-stage renal disease.

Morphometric and histological parameters in veins of diabetic patients undergoing brachiocephalic fistula placement

Diabetic patients with end-stage renal failure have higher rates of arteriovenous failures when compared with nondiabetics. The aim was to compare differences in indicators of vascular remodeling and endothelial dysfunction in veins of patients with or without diabetes at the time of surgical placement. In this prospective observational trial, vein samples were collected from patients when a brachiocephalic fistula was created. Morphometric measurements and extent of fibrosis were determined using Image J software. Histological analysis, for the presence of myofibroblasts and level of endothelial nitric oxide synthase, was performed by immunohistochemical staining and scored in semi-quantitative manner. Asymmetric dimethylarginine was determined at the time of access placement. Comparison of diabetics and nondiabetics was performed using Wilcoxon rank sum and Fisher's exact tests. Eighteen patients were included; 10 were diabetics. There was a significant difference in the measurement of vein area between groups, with diabetic vein samples having larger luminal area of average 832,001.18 μm(2) (317,582.17-3,695,670.36, P = 0.04). The maximal intimal to medial thickness ratio was higher in diabetic vein samples (0.71 vs. 0.24, P = 0.03) along with statistically significant higher maximal intimal thickness (312.12 vs. 115.14 μm, P = 0.03). There is a significant difference in vascular wall remodeling between diabetics and nondiabetics at the level of the cephalic vein at the time of brachiocephalic placement. The unexpected finding of significantly larger luminal area in diabetic veins could be a major factor positively affecting brachiocephalic outcomes in otherwise impaired remodeling in this patient population.

The impact of endothelial progenitor cells on restenosis after percutaneous angioplasty of hemodialysis vascular access

Objective

We prospectively investigate the relation between baseline circulating endothelial progenitor cells and the subsequent development of restenosis after angioplasty of hemodialysis vascular access.

Background

Effect of angioplasty for hemodialysis vascular access is greatly attenuated by early and frequent restenosis. Circulating endothelial progenitor cells (EPCs) play a key role in vascular repair but are deficient in hemodialysis patients.

Method

After excluding 14 patients due to arterial stenosis, central vein stenosis, and failed angioplasty, 130 patients undergoing angioplasty for dysfunctional vascular access were prospectively enrolled. Flow cytometry with quantification of EPC markers (defined as CD34⁺, CD34⁺KDR⁺, CD34⁺KDR⁺CD133⁺) in peripheral blood immediately before angioplasty procedures was used to assess circulating EPC numbers. Patients were followed clinically for up to one year after angioplasty.

Results

During the one-year follow-up, 95 patients (73%) received interventions for recurrent access dysfunction. Patients in the lower tertile of CD34⁺KDR⁺ cell count had the highest restenosis rates (46%) at three month (early restenosis), compared with patients in the medium and upper tertiles of CD34⁺KDR⁺ cell count (27% and 12% respectively, p = 0.002). Patients in the lower tertile of CD34⁺KDR⁺ cell count received more re-interventions during one year. Patients with early restenosis had impaired EPC adhesive function and increased senescence and apoptosis. In multivariate analysis, the CD34⁺KDR⁺ and CD34⁺KDR⁺CD133⁺ cell counts were independent predictors of target-lesion early restenosis.

Conclusion

Our results suggest that the deficiency of circulating EPCs is associated with early and frequent restenosis after angioplasty of hemodialysis vascular access.

Predictors of patency after balloon angioplasty in hemodialysis fistulas: a systematic review

Percutaneous transluminal angioplasty (PTA) is an established treatment for dysfunctional hemodialysis fistulas. This article systematically reviews evidence for predictors of patency after PTA. Outcomes assessed were primary, assisted primary, and secondary patency after intervention, and findings were summarized descriptively. This review included 11 nonrandomized observational studies of 965 fistulas in 939 patients. Follow-up ranged from 0 days to 10 years. Study quality was overall suboptimal. Newer fistulas and longer lesion length may be associated with primary patency loss after PTA. Further studies are needed to confirm these findings, to identify potentially modifiable factors, and to guide the testing of new endovascular devices.

Novel paradigms for dialysis vascular access: downstream vascular biology--is there a final common pathway?

Vascular access dysfunction is a major cause of morbidity and mortality in hemodialysis patients. The most common cause of vascular access dysfunction is venous stenosis from neointimal hyperplasia within the perianastomotic region of an arteriovenous fistula and at the graft-vein anastomosis of an arteriovenous graft. There have been few, if any, effective treatments for vascular access dysfunction because of the limited understanding of the pathophysiology of venous neointimal hyperplasia formation. This review will (1) describe the histopathologic features of hemodialysis access stenosis; (2) discuss novel concepts in the pathogenesis of neointimal hyperplasia development, focusing on downstream vascular biology; (3) highlight future novel therapies for treating downstream biology; and (4) discuss future research areas to improve our understanding of downstream biology and neointimal hyperplasia development.

Changes in ADMA and TAFI levels after stenting in coronary artery disease patients

The aim of this study was to examine the contribution of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS) and a novel marker of vascular endothelial dysfunction, and thrombin-activatable fibrinolysis inhibitor (TAFI), a risk factor for venous thrombosis, to the predisposition of coronary restenosis following stent implantation in coronary artery disease (CAD) patients. Thirty-seven patients with CAD were recruited from the Kobry El Obba Military Hospital, Cairo, Egypt. The patients were hospitalized for coronary angiography and coronary stenting (CS). Overnight fasting blood samples were collected from patients prior to CS and four months later for the determination of plasma ADMA and TAFI levels. The patients underwent follow-up coronary angiography to reveal in-stent restenosis. The results showed that plasma ADMA levels in CAD patients were significantly higher than those reported for healthy subjects. ADMA levels were significantly increased by 30% in CAD patients four months following CS. CAD patients who developed in-stent restenosis had a 35% increase in ADMA levels following CS. TAFI levels were not significantly changed after CS in CAD patients or in any of the subgroups. In conclusion, ADMA, but not TAFI, is linked to the predisposition of in-stent restenosis following CS.

Antiretrovirals induce endothelial dysfunction via an oxidant-dependent pathway and promote neointimal hyperplasia

Human immunodeficiency virus-1 antiretroviral treatment is associated with an increased incidence of atherosclerosis. We hypothesized that antiretrovirals directly impair endothelial function after short-term exposure and that with chronic exposure, this dysfunction promotes a proliferative response, inducing neointimal hyperplasia, thus contributing to vascular lesion formation. To test this hypothesis, we treated mice with the nucleoside reverse transcriptase inhibitor azidothymidine (AZT), the protease inhibitor indinavir, or AZT + indinavir. Treatment with AZT or AZT + indinavir for 5 days impaired endothelium-dependent vessel relaxation. Though indinavir treatment alone did not alter vessel relaxation, it potentiated the impairment of endothelium-dependent relaxation induced by AZT. Coadministration of the antioxidant Mn (III) tetrakis (1-methyl-4-pyridyl) porphyrin attenuated antiretroviral-induced endothelial dysfunction, suggesting that oxidant production may have a causal role in the observed endothelial dysfunction. To test whether the antiretrovirals promote a proliferative response following endothelial dysfunction, we treated mice with antiretrovirals for 14 days and then induced a carotid endothelial injury. Two weeks later, we observed a dramatic increase in neointimal formation in all antiretroviral-treated animals, and the newly formed neointima was comprised mainly of proliferated smooth muscle cells. Although a functional endothelium surrounding the lesioned area and re-endothelialization across the area of injury is important in reducing proliferation in this model, we tested whether the neointimal hyperplasia was associated with endothelial dysfunction. Plasma levels of asymmetric dimethylarginine, a biomarker of endothelial dysfunction, increased after treatment with indinavir or AZT + indinavir. On the other hand, treatment with AZT or AZT + indinavir increased endothelial vascular cell adhesion molecule staining. We conclude that short-term treatment with antiretrovirals elicited a direct impairment in endothelial function, in part via an oxidant-dependent pathway. These antiretrovirals also exacerbated injury-induced vascular smooth muscle cell proliferation and neointimal hyperplasia, likely because of their inhibition of endothelial function.

Characterization of a model of an arteriovenous fistula in the rat: the effect of L-NAME

Vascular access dysfunction contributes to the mortality of patients undergoing chronic hemodialysis. The present study analyzed the changes that evolve in a femoral arteriovenous fistula in the rat. The venous segment of this model exhibited, at 1 week, activation of pro-inflammatory transcription factors and up-regulation of pro-inflammatory, proliferative, procoagulant, and profibrotic genes; and at 4 weeks, the venous segment displayed neointimal hyperplasia, smooth muscle proliferation, and thrombus formation. These changes were accompanied by endothelial (e) nitric oxide synthase (NOS) and inducible (i) NOS up-regulation. The administration of NG-nitro-L-arginine methyl ester, an inhibitor of NOS activity, increased venous neointimal hyperplasia and pro-inflammatory gene expression (monocyte chemoattractant protein-1 and cytokine-induced neutrophil chemoattractant-1), increased systolic blood pressure, and decreased blood flow through the fistula. In another hypertensive model, the rat subtotal nephrectomy model, venous neointimal hyperplasia in the arteriovenous fistula was also exacerbated. We conclude that this arteriovenous fistula model recapitulates the salient features observed in dysfunctional, hemodialysis arteriovenous fistulas, and that venous neointimal hyperplasia is exacerbated when this model is superimposed in two different models of systemic hypertension. Since the uremic milieu contains increased amounts of asymmetric dimethylarginine, we speculate that such accumulation of this endogenous inhibitor of NOS, by virtue of its pressor or nitric oxide-depleting effects, or a combination thereof, may contribute to the limited longevity of arteriovenous fistulas used for hemodialysis.

Advances and new frontiers in the pathophysiology of venous neointimal hyperplasia and dialysis access stenosis

Hemodialysis vascular access dysfunction is a major cause of morbidity and mortality in hemodialysis patients. The most common cause of this vascular access dysfunction is venous stenosis as a result of venous neointimal hyperplasia within the perianastomotic region (arteriovenous fistula) or at the graft-vein anastomosis (polytetrafluoroethylene, or PTFE, grafts). There have been few effective treatments to date for venous neointimal hyperplasia, in part, because of the poor understanding of the pathogenesis of venous neointimal hyperplasia. Therefore, this article will (1) describe the pathology of hemodialysis access stenosis in arteriovenous fistulas and grafts, (2) review and describe both current and novel concepts in the pathogenesis of neointimal hyperplasia formation, (3) discuss current and future novel therapies for treating venous neointimal hyperplasia, and (4) suggest future research areas in the field of hemodialysis vascular access dysfunction.