Arteriovenous Hemodialysis Access Stenosis Diagnosed by Duplex Doppler Ultrasonography: A Review

The Alpha to Omega of Dialysis Access: Arteriovenous Fistula and Graft (Part 1)

Background: Vascular access is a critical determinant of hemodialysis efficacy in patients with end-stage kidney disease (ESKD). The choice between arteriovenous fistulas (AVFs) and arteriovenous grafts (AVGs) influences long-term dialysis outcomes, with AVFs offering superior patency but higher maturation failure rates and AVGs providing immediate usability at the expense of increased complications. Recent advancements in endovascular techniques and biomaterials have introduced novel approaches to optimizing vascular access. Purpose: This review examines the latest evidence on AVF and AVG creation, focusing on factors affecting maturation, long-term patency, and emerging minimally invasive techniques, such as percutaneous AVF creation, to enhance hemodialysis access outcomes. Research Design: A systematic review of current literature, clinical guidelines, and innovations in vascular access for dialysis patients was conducted. Emphasis was placed on comparative effectiveness studies, patency and complication rates, and new endovascular approaches. Study Sample: Data were sourced from clinical trials, registry reports, and systematic reviews evaluating AVF and AVG outcomes, as well as emerging endovascular fistula technologies. Data Collection and/or Analysis: Key parameters such as patency rates, infection rates, thrombosis incidence, and maturation success were analyzed. Particular attention was given to procedural innovations, including bioengineered grafts and percutaneous fistula creation, assessing their impact on long-term dialysis access viability. Results: AVFs maintain superior long-term patency but are hindered by primary failure rates, necessitating interventions for maturation. AVGs, while more prone to infection and thrombosis, offer a viable alternative when native vessels are unsuitable. Endovascular AVF creation has demonstrated high technical success and promising long-term outcomes, reducing the need for traditional surgical approaches. Advances in biomaterials and adjunctive pharmacologic therapies may further improve vascular access durability. Conclusions: Individualized vascular access planning remains essential to optimizing hemodialysis outcomes. The evolution of minimally invasive techniques, coupled with improved patient selection criteria and emerging biomaterials, offers new opportunities for enhancing dialysis access longevity. Future research should focus on refining endovascular approaches and integrating novel technologies to minimize complications and improve access patency.

Ankle-brachial index associates with arteriovenous fistula stenosis

BACKGROUND

Arteriovenous fistula (AVF) stenosis is associated with pre-existing arterial atherosclerosis of AVF and results in significant morbidity and hospitalization for hemodialysis patients. The ankle brachial index (ABI) is a noninvasive method of assessing atherosclerosis. This study was to examine whether ABI is a significant predictor for AVF stenosis.

METHODS

This was a retrospective, longitudinal cohort study. Patients with hemodialysis between 1 January 2016 and 31 December 2022 were reviewed. ABI was assessed in January 2016. AVF stenosis was diagnosed by fistulography.

RESULTS

A total of 82 patients were included. Forty-two patients experienced AVF stenosis. The univariate logistic regression analysis showed that AVF stenosis was associated with age (OR: 1.045, p = 0.033), DM status (OR: 5.529, p = 0.013), 7-year averaged cholesterol level (OR: 1.018, p = 0.034), 7-year averaged triglyceride level (OR: 1.007, p = 0.017), and ABI (OR: 0.011, p < 0.001). In multivariate logistic regression analysis, ABI was a strong predictor for AVF stenosis (OR: 0.036, p = 0.023). Then, a cut-off point of ABI with optimal sensitivity and specificity for AVF stenosis was 1.01. An analysis of time to events with adjustment for other variables showed that patients with ABI < 1.01 were significantly associated with AVF stenosis (HR: 3.859, p < 0.001).

CONCLUSIONS

ABI below 1.01 was associated with AVF stenosis. This finding may be useful in tailoring surveillance programs for monitoring AVF function.

Assessing the Value of Further Investment in R&D Using Mixed Methods: A Case Study of Biosensor-Integrated Arteriovenous Grafts

This study illustrates the utility of a mixed-methods approach in assessing the value of an example novel technology-biosensor-integrated self-reporting arteriovenous grafts (smart AVGs). Currently in preclinical development, the device will detect arteriovenous graft stenosis (surveillance-only use case) and treat stenosis (interventional use case). The approach to value assessment adopted in this study was multifaceted, with one stage informing the next and comprised a stakeholder engagement with clinical experts to explore the device's clinical value, a cost-utility analysis (CUA) from a US Medicare perspective to estimate pricing headroom, and an investment model estimating risk-adjusted net present value analysis (rNPVs) to determine commercial viability. The stakeholder engagement suggested that it would currently be difficult to establish the current value of the surveillance-only use case due to the lack of well-established interventions for preclinical stenosis. Based on this, the CUA focused on the interventional use case and estimated economically justifiable prices at assumed effectiveness levels. Using these prices, rNPVs were estimated over a range of scenarios. This value assessment informs early decision-making on health technology R&D by identifying the conditions (including clinical study success, potential market size and penetration, market access strategies, and assumptions associated with CUA) under which investment may be considered attractive.

Classifications of haemodialysis vascular access stenosis: a scoping review

OBJECTIVES

Vascular access (VA) stenoses play a significant role in the morbidity of the haemodialysed population. Classifications for diagnosis, assessment and proposal of treatment strategies can be useful clinical and methodological tools. This review aims to present a comprehensive summary and propose further methodological approaches.

DESIGN

A systematic review of the literature, evaluating classifications for dialysis-related VA stenosis.

DATA SOURCES

Web of Science, Scopus, PubMed, Google Scholar and the ClinicalTrials.gov registry were searched from inception to 7 December 2024.

ELIGIBILITY CRITERIA

All articles containing classifications regarding dialysis VA were eligible, with no restrictions on the study type or language of the full text.

DATA EXTRACTION AND SYNTHESIS

Two independent researchers performed the search and initial screening. Four vascular surgeons assessed the included classifications using a modified Buchbinder's critical appraisal tool to evaluate quality.

RESULTS

From 4771 screened papers, 59 full-text papers were retrieved and 24 articles contained classifications. Three classifications were dedicated to VA stenosis, all based on the anatomical location of lesions. According to the modified Buchbinder's appraisal, the classifications were assessed as moderate-to-good quality. The literature disposes of immense inconsistency in terms of the definition of significant stenosis indicated for treatment.

CONCLUSIONS

VA significant stenosis and its classification is a non-uniformly understood issue with many different criteria and categorisations. This basic methodological problem leads to inconsistent results. We recommend the unification of the criteria and their validation in prospective studies.

Fluid-structure interaction in a follow-up study of arterio-venous fistula maturation

Arteriovenous fistula (AVF) is the preferred vascular access for hemodialysed patients. AVF is created surgically using the patient's artery and vein. Once the connection (anastomosis) is made, the maturation process begins. Studies have shown that most AVFs do not survive beyond one year. This study presents fluid-structure interaction (FSI) modelling of non-Newtonian blood flow through an end-to-side radio-cephalic AVF, investigated weekly during a 15-week follow-up period and 1.5 years postoperatively using ultrasound methods. The aim was to collect qualitative and quantitative data regarding changes in hemodynamics and alterations in the walls of AVF vasculature. Different material properties were assigned to the artery, suture zone (anastomosis), and vein, while the stiffening of the venous arm over time was also modelled. The proposed FSI methodology can be implemented in future follow-up studies involving groups of patients. The main findings revealed: a) counter-rotating vortices in the anastomosis cross-section affecting local pressure conditions; b) different temporal progression of vorticity, shear strain rate, and turbulent kinetic energy and similarity of the temporal progression of WSS obtained under the assumptions of the rigid-walled and FSI; c) a negligible low-WSS zone in the presented thrombosis-free AVF; d) migration of the zone of maximal temporal wall deformation over time.

Arterio-Venous Fistula Calcifications-Risk Factors and Clinical Relevance

(1) Background: Arterio-venous fistulas (AVFs) are considered the gold-standard vascular access (VA) in patients on maintenance hemodialysis (HD) therapy. AVF calcifications represent a less studied VA related complication, even though HD patients are at a higher risk for extraosseous calcifications. The aim of this study is to assess the prevalence and risk factors of AVF calcifications, as well as the 5-year impact on AVF functionality and on overall mortality. (2) Methods: We conducted a 5-year prospective study including 161 patients on maintenance HD therapy. At baseline, we collected data related to VA history, comorbidities, demographics, subjective global assessment scale (SGA), and biochemical parameters. All patients underwent a complete AVF ultrasound and we recorded AVF blood flow and the presence of AVF calcifications, stenoses, and aneurysms. (3) Results: In our study, we found an AVF calcification prevalence of 39%. In a univariate analysis, we found that patients with AVF calcifications were associated with other AVF complications as well (stenoses, aneurysms), had longer AVF and HD vintage, as well as higher serum calcium and PTH values. In a multivariate analysis, we found that patients with a longer HD vintage and higher calcium values were independently associated with AVF calcifications. AVF calcifications did not affect 5-year fistula patency, nor were they associated with a higher mortality risk in our group of patients. (4) Conclusions: AVF calcifications were a frequent finding in our analysis, but their presence does not seem to affect the 5-year AVF patency.

Prediction of Arteriovenous Access Dysfunction by Mel Spectrogram-based Deep Learning Model

Background: The early detection of arteriovenous (AV) access dysfunction is crucial for maintaining the patency of vascular access. This study aimed to use deep learning to predict AV access malfunction necessitating further vascular management. Methods: This prospective cohort study enrolled prevalent hemodialysis (HD) patients with an AV fistula or AV graft from a single HD center. Their AV access bruit sounds were recorded weekly using an electronic stethoscope from three different sites (arterial needle site, venous needle site, and the midpoint between the arterial and venous needle sites) before HD sessions. The audio signals were converted to Mel spectrograms using Fourier transformation and utilized to develop deep learning models. Three deep learning models, (1) Convolutional Neural Network (CNN), (2) Convolutional Recurrent Neural Network (CRNN), and (3) Vision Transformers-Gate Recurrent Unit (ViT-GRU), were trained and compared to predict the likelihood of dysfunctional AV access. Results: Total 437 audio recordings were obtained from 84 patients. The CNN model outperformed the other models in the test set, with an F1 score of 0.7037 and area under the receiver operating characteristic curve (AUROC) of 0.7112. The Vit-GRU model had high performance in out-of-fold predictions, with an F1 score of 0.7131 and AUROC of 0.7745, but low generalization ability in the test set, with an F1 score of 0.5225 and AUROC of 0.5977. Conclusions: The CNN model based on Mel spectrograms could predict malfunctioning AV access requiring vascular intervention within 10 days. This approach could serve as a useful screening tool for high-risk AV access.

Vascular Access Considerations in Home Hemodialysis

There is a global interest in expanding home dialysis utilization among patients with ESKD. Home hemodialysis (HHD) is an appealing KRT option for this population because of its multiple clinical and quality of life benefits. Central to successful HHD is the establishment and maintenance of a functioning vascular access that serves as a patient's lifeline while on therapy. While the selection of a vascular access type is influenced by individual patient circumstances, the arteriovenous fistula is generally the preferred access method. Training patients to use their dialysis access requires attention to safety, risk management, and monitoring for complications to minimize adverse events and technique failure. Policies incorporating systematic frameworks for quality improvement and assurance, in conjunction with the measurement of metrics relating to vascular access, are tools that should be used by HHD programs to enhance the value of care delivered. In this perspective, we aim to describe what is currently known about the various vascular access options in HHD and to elucidate what needs to be taken into consideration in the selection and care of this access.

Health-care Professionals' Perspectives on Ultrasound Evaluation of Arteriovenous Hemodialysis Fistula: A Narrative Review

Arteriovenous hemodialysis fistulas play a critical role in maintaining life on hemodialysis. With the growing use of Doppler ultrasound in nephrology, its utility has expanded to improve the prognosis and quality of life of patients receiving hemodialysis. On a fistula care team, different health-care professionals, including nephrologists, dialysis technicians, and surgeons or vascular interventionalists, require different information. This review article comprehensively explains how Doppler ultrasound evaluation can be beneficial in the management of arteriovenous fistulas from different perspectives of health-care professionals. The article also introduces the pathophysiology of arteriovenous fistula disease and provides a thorough introduction to the use of Doppler ultrasound for the evaluation of arteriovenous fistulas and their associated diseases, addressing the need for a comprehensive understanding among ultrasound practitioners.

Disturbed flow in the juxta-anastomotic area of an arteriovenous fistula correlates with endothelial loss, acute thrombus formation, and neointimal hyperplasia

Clinical failure of arteriovenous neointimal hyperplasia (NIH) fistulae (AVF) is frequently due to juxta-anastomotic NIH (JANIH). Although the mouse AVF model recapitulates human AVF maturation, previous studies focused on the outflow vein distal to the anastomosis. We hypothesized that the juxta-anastomotic area (JAA) has increased NIH compared with the outflow vein. AVF was created in C57BL/6 mice without or with chronic kidney disease (CKD). Temporal and spatial changes of the JAA were examined using histology and immunofluorescence. Computational techniques were used to model the AVF. RNA-seq and bioinformatic analyses were performed to compare the JAA with the outflow vein. The jugular vein to carotid artery AVF model was created in Wistar rats. The neointima in the JAA shows increased volume compared with the outflow vein. Computational modeling shows an increased volume of disturbed flow at the JAA compared with the outflow vein. Endothelial cells are immediately lost from the wall contralateral to the fistula exit, followed by thrombus formation and JANIH. Gene Ontology (GO) enrichment analysis of the 1,862 differentially expressed genes (DEG) between the JANIH and the outflow vein identified 525 overexpressed genes. The rat jugular vein to carotid artery AVF showed changes similar to the mouse AVF. Disturbed flow through the JAA correlates with rapid endothelial cell loss, thrombus formation, and JANIH; late endothelialization of the JAA channel correlates with late AVF patency. Early thrombus formation in the JAA may influence the later development of JANIH.NEW & NOTEWORTHY Disturbed flow and focal endothelial cell loss in the juxta-anastomotic area of the mouse AVF colocalizes with acute thrombus formation followed by late neointimal hyperplasia. Differential flow patterns between the juxta-anastomotic area and the outflow vein correlate with differential expression of genes regulating coagulation, proliferation, collagen metabolism, and the immune response. The rat jugular vein to carotid artery AVF model shows changes similar to the mouse AVF model.

Evaluation of arteriovenous fistula for hemodialysis with a new generation digital stethoscope: a pilot study

BACKGROUND AND AIMS

The management of complications of arteriovenous fistula (AVF) for hemodialysis, principally stenosis, remains a major challenge for clinicians with a substantial impact on health resources. Stenosis not infrequently preludes to thrombotic events with the loss of AVF functionality. A functioning AVF, when listened by a stethoscope, has a continuous systolic-diastolic low-frequency murmur, while with stenosis, the frequency of the murmur increases and the duration of diastolic component decreases, disappearing in severe stenosis. These evidences are strictly subjective and dependent from operator skill and experience. New generation digital stethoscopes are able to record sound and subsequently dedicated software allows to extract quantitative variables that characterize the sound in an absolutely objective and repeatable way. The aim of our study was to analyze with an appropriate software sounds from AVFs taken by a commercial digital stethoscope and to investigate the potentiality to develop an objective way to detect stenosis.

METHODS

Between September 2022 and January 2023, 64 chronic hemodialysis (HD) patients were screened by two blinded experienced examiners for recognized criteria for stenosis by Doppler ultrasound (DUS) and, consequently, the sound coming from the AVFs using a 3 M™ Littmann® CORE Digital Stethoscope 8570 in standardized sites was recorded. The sound waves were transformed into quantitative variables (amplitude and frequency) using a sound analysis software. The practical usefulness of the core digital stethoscope for a quick identification of an AVF stenosis was further evaluated through a pragmatic trial. Eight young nephrologist trainees underwent a simple auscultatory training consisting of two sessions of sound auscultation focusing two times on a "normal" AVF sound by placing the digital stethoscope on a convenience site of a functional AVF.

RESULTS

In 48 patients eligible, all sound components displayed, alone, a remarkable diagnostic capacity. More in detail, the AUC of the average power was 0.872 [95% CI 0.729-0.951], while that of the mean normalized frequency was 0.822 [95% 0.656-0.930]. From a total of 32 auscultations (eight different block sequences, each one comprising four auscultations), the young clinicians were able to identify the correct sound (stenosis/normal AVF) in 25 cases, corresponding to an overall accuracy of 78.12% (95% CI 60.03-90.72%).

CONCLUSIONS

The analysis of sound waves by a digital stethoscope permitted us to distinguish between stenotic and no stenotic AVFs. The standardization of this technique and the introducing of data in a deep learning algorithm could allow an objective and fast method for a frequent monitoring of AVF.