Stent graft versus balloon angioplasty for failing dialysis-access grafts

Non-compliance with randomised allocation and missing outcome data in randomised controlled trials evaluating surgical interventions: a systematic review

Background

Randomised controlled trials are widely acknowledged as the gold standard in medical research although their validity can be undermined by non-compliance with the randomly allocated treatment and missing data. Due to the nature of the intervention, surgical trials face particular threat to compliance and data collection. For example, ineligibility for the intervention may only become apparent once the operation has commenced. It is unclear how such cases are reported and handled.

Objective

The objective was to assess non-compliance and missing data in reports of trials of surgical interventions.

Methods

Searches for reports of trials involving at least one surgical procedure and published in 2010 were carried out in the Medical Literature Analysis and Retrieval System Online (MEDLINE^®). Data on missing data, non-compliance and methods of handling missing data were extracted from full texts. Descriptive data analyses were carried out on the data.

Results

Forty-five (55 %) studies reported non-compliance with treatment allocation and 52 (63 %) reported primary outcome missing data. The median levels of non-compliance and missing data were 2 % [IQR (0, 5), range (0–29)] and 6 % [IQR (0, 15), range (0–57)], respectively. Fifty-two (63 %) studies analysed as randomised, 17 (21 %) analysed per protocol and 3 (4 %) analysed as treated. Complete case analysis was the most common method used to deal with missing data, 35/52 (67 %).

Conclusions

The reporting of non-compliance to allocation and the handling of missing data were typically suboptimal. There is still room for improvement on the use of the CONSORT statement particularly in accounting for study participants. Transparency in reporting would facilitate evidence synthesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1364-9) contains supplementary material, which is available to authorized users.

Promises for the Future: Minimally Invasive Fistula Creation

The surgical creation of an autogenous fistula is the vascular access of choice for delivery of hemodialysis. However, it is prone to relatively high rates of maturation failure, stenosis and thrombosis. Most of these problems can be attributed to the surgical creation itself. Percutaneous or endovascular creation of an autogenous fistula offers the possibility of overcoming some of these problems.

Early Experience With a Novel Hybrid Vascular Graft for Hemodialysis Access Creation in Patients With Disadvantaged Anatomy

Purpose: To describe the use of the Hybrid vascular graft in disadvantaged anatomy for hemodialysis access creation and compare outcomes to standard-wall polytetrafluoroethylene (PTFE) grafts. Methods: In a retrospective analysis, 25 patients (mean age 65±14 years; 13 men) who received the Hybrid graft were compared with 35 contemporaneous patients (mean age 63±12 years; 20 men) who received a standard PTFE graft for hemodialysis access over a 2-year period. Criteria for Hybrid graft placement were (1) exhausted or inadequate peripheral veins for arteriovenous fistula (AVF) creation and concomitant small target veins that precluded conventional PTFE graft placement, (2) previous graft anastomosis or a stent in the venous target at the level of the axilla, or (3) failed brachial-basilic or brachial-brachial upper arm transposition AVF with a small target vein at the axilla. Efficacy, anatomic and clinical considerations, and technique were reviewed; patency rates, complications, and reinterventions were examined. Results: Technical success was achieved in all cases, and all grafts were usable for hemodialysis. Seven of 25 Hybrid patients required stent-graft extensions and 3 patients required angioplasty to improve venous outflow at the time of Hybrid graft insertion. Three of 35 standard PTFE graft patients required angioplasty to improve venous outflow at the time of graft insertion. There was no perioperative mortality or procedure-related morbidity in either group. Median follow-up was 21 months. The patient survival estimate was 66% at 2 years. Estimated primary patency (24% vs 18%, p>0.05), assisted primary patency (34% vs 28%; p>0.05), and secondary patency rates (40% vs 38%, p≥0.05) at 24 months were equivalent for Hybrid vs PTFE grafts, respectively. Venous hypertension was not a complication following Hybrid graft implantation but was seen in 2 patients with the standard PTFE graft. Conclusion: The Hybrid graft offers a safe, technically effective alternative for patients with disadvantaged anatomy requiring hemodialysis access and has comparable outcomes to standard PTFE grafts. Further clinical experience and long-term data are required for determining the proper utility of this device in chronic dialysis-dependent patients.

Assessment of the Effectiveness of Percutaneous Transluminal Balloon Angioplasty for Failing or Nonmaturing Arteriovenous Fistulae for Hemodialysis

BACKGROUND

Autologous arteriovenous (A-V) fistulae are the recommended arteriovenous access for long-term dialysis in chronic renal failure patients. However, the rate of nonmaturity and failure is still significant. The present study aimed at salvaging fistulas using percutaneous transluminal balloon angioplasty (PTA).

METHODS

Thirty-two patients with nonmaturing or failing fistulas were included, to which they were subjected to PTA with preintervention and postintervention fistulograms to assess the success rate in restoring the fistulae's patency and function.

RESULTS

Salvage rate was 26 of 32 fistulas (81.3%) in which the fistulas regain their usability for hemodialysis at least for 3 months of follow-up, 4 cases (12.5%) persist nonmature and 2 cases (6.3%) were not used for stenosis.

CONCLUSIONS

PTA is a safe and effective method for treating nonmature and failing native A-V fistulas.

Dual stent migration to the heart and pulmonary artery

The practice of intravascular stenting largely grew out of the concept of stenting the coronaries in acute myocardial infarction. According to the recent United States Renal Data System data registry, there has been a significant increase in endovascular intervention (1.8-fold increase-from 52,380 to 98,148) with a 2.2-fold increase in stent deployment in hemodialysis access (3792-8514). With the increasing use of endovascular stents in the management of dialysis access stenosis, the incidence of stent-related complications has increased significantly. Stent-related complications include stent restenosis, thrombosis (narrowing of the vessel lumen and being a nidus for thombus formation), stent shortening, stent fracture, stent infection, and stent migration. Physiologic variation in the diameter of veins due to respiration, which along with the geometry of the stent, can lead to a shortening lengthening of the stent-resulting in poor wall contact or high-speed impact of shock; in the case of trauma, mechanical bucking can result in tortuous blood vessels thereby resulting in stent migration (however proving this association was not the aim of this article). We report a case of a 44-year-old female with end-stage renal disease on hemodialysis, with stent placement to treat a compromised arteriovenous graft. There have been many cases of stent migration in the past; however, this is the first case of dual stent migration to the heart and pulmonary artery from an unusual (lower extremity) arteriovenous graft location.

A Patient with Recurrent Arteriovenous Graft Thrombosis

Arteriovenous grafts (AVGs) are prone to frequent thrombosis that is superimposed on underlying hemodynamically significant stenosis, most commonly at the graft-vein anastomosis. There has been great interest in detecting AVG stenosis in a timely fashion and performing preemptive angioplasty, in the belief that this will prevent AVG thrombosis. Three surveillance methods (static dialysis venous pressure, flow monitoring, and duplex ultrasound) can detect AVG stenosis. Whereas observational studies have reported that surveillance with preemptive angioplasty substantially reduces AVG thrombosis, randomized clinical trials have failed to confirm such a benefit. There is a high frequency of early AVG restenosis after angioplasty caused by aggressive neointimal hyperplasia resulting from vascular injury. Stent grafts prevent AVG restenosis better than balloon angioplasty, but they do not prevent AVG thrombosis. Several pharmacologic interventions to prevent AVG failure have been evaluated in randomized clinical trials. Anticoagulation or aspirin plus clopidogrel do not prevent AVG thrombosis, but increase hemorrhagic events. Treatment of hyperhomocysteinemia does not prevent AVG thrombosis. Dipyridamole plus aspirin modestly decreases AVG stenosis or thrombosis. Fish oil substantially decreases the frequency of AVG stenosis and thrombosis. In patients who have exhausted all options for vascular access in the upper extremities, thigh AVGs are a superior option to tunneled internal jugular vein central vein catheters (CVCs). An immediate-use AVG is a reasonable option in patients with recurrent CVC dysfunction or infection. Tunneled femoral CVCs have much worse survival than internal jugular CVCs.

Percutaneous Transluminal Angioplasty in Japan: Five-Center Investigation

Purpose

Percutaneous transluminal angioplasty (PTA) is the first-line treatment for vascular access stenosis. To our knowledge, multicenter clinical research of PTA has not been reported in Japan. We examined the efficacy and safety of PTA for arteriovenous fistula (AVF) and arteriovenous graft (AVG) in five centers of Japan.

Methods

Three hundred cases of angioplasty for AVF and 300 for AVG were examined in three centers each. A hundred consecutive patients from each center who underwent PTA for AVG or AVF prior to March 2014 and met the inclusion criteria were searched retrospectively. Primary patency rates were estimated using the Kaplan-Meier method.

Results

The mean age was 69.3 ± 11.2 years in the AVF group and 70.2 ± 11.9 years in the AVG group. The anatomical success rates were 51.7% (155 of 300) in the AVF group and 72.0% (216 of 300) in the AVG group. The clinical success rates were 99.7% (299 of 300) in the AVF group and 100% (300 of 300) in the AVG group. A total of 25 complications (4.17%) were encountered in both groups including one major complication (0.17%). The primary patency was 99.0% at 1 month, 87.9% at 3 months and 51.7% at 6 months in the AVF group, and 96.0% at 1 month, 64.8% at 3 months and 20.4% at 6 months in the AVG group.

Conclusions

The clinical success rate of PTA in five centers was relatively high and a major complication rate was only 0.17%. However, anatomical success rates were low comparing with the previous studies and the primary patency rates were inferior to the past data.

Balloon angioplasty for low-flow access

The common mechanism for low access flow is intimal hyperplasia leading to stenosis within the access circuit. Balloon angioplasty (percutaneous transluminal angioplasty, PTA) remains the mainstay of treatment despite multiple technologies introduced in the past. New technologies continue to be introduced in an effort to improve on outcomes of angioplasty. This article briefly reviews the use of and outcomes of PTA, technologies, past, present and future as well as some of the questions that remain unanswered with PTA.

Influence of drugs on arteriovenous vascular access dysfunction

Vascular access dysfunction, due to venous stenosis at the vein-artery anastomosis in arteriovenous fistulas and vein-graft anastomosis in synthetic arteriovenous grafts, is a major cause of morbidity and mortality in dialysis patients. The two overarching approaches to prevent and treat vascular access dysfunction are from systemic or local (including endovascular and perivascular) routes. However, there are currently very few effective therapies to treat vascular access dysfunction. This article will review major studies evaluating systemic, endovascular, and perivascular therapies for vascular access dysfunction. Ongoing research to evaluate novel innovations to prevent and/or manage vascular access dysfunction appears promising.

Drug-eluting versus plain balloon angioplasty for the treatment of failing dialysis access: final results and cost-effectiveness analysis from a prospective randomized controlled trial (NCT01174472)

OBJECTIVE

To report the final results and cost-effectiveness analysis of a prospective randomized controlled trial investigating drug-eluting balloon (DEB) versus plain balloon angioplasty (BA) for the treatment of failing dialysis access (NCT01174472).

METHODS

40 patients were randomized to angioplasty with either DEB (n=20) or BA (n=20) for treatment of significant venous stenosis causing a failing dialysis access. Both arteriovenous fistulas (AVF) and synthetic arteriovenous grafts (AVG) were included. Angiographic follow up was scheduled every two months. Primary endpoints were technical success and target lesion primary patency at 1 year. Cumulative and survival analysis was performed. Incremental net benefit (INB) and incremental cost effectiveness ratio (ICER) were calculated and the cost-effectiveness acceptability curve (CEAC) was drawn.

RESULTS

Baseline variables were equally distributed between the two groups. At 1 year, cumulative target lesion primary patency was significantly higher after DEB application (35% vs. 5% after BA, p<0.001). Overall, median primary patency was 0.64 years in case of DEB vs. 0.36 years in case of BA (p=0.0007; unadjusted HR=0.27 [95%CI: 0.13-0.58]; Cox adjusted HR=0.23 [95%CI: 0.10-0.50]). ICER was 2198 Euros (€) per primary patency year of dialysis access gained. INB was 1068€ (95%CI: 31-2105€) for a willingness-to-pay (WTP) threshold of 5000€ (corresponding acceptability probability >97%).

CONCLUSION

DEB angioplasty may be a cost-effective option that significantly improves patency after angioplasty of venous stenoses of failing vascular dialysis access. Further large-scale randomized trials are warranted.

Paclitaxel-coated versus plain balloon angioplasty for dysfunctional arteriovenous fistulae: one-year results of a prospective randomized controlled trial

PURPOSE

To report 1-year results of a single-center randomized controlled trial comparing paclitaxel-coated balloon (PCB) versus high-pressure plain balloon angioplasty for the treatment of failing arteriovenous fistulae (AVFs).

MATERIALS AND METHODS

Forty patients (26 men; mean age, 61 y ± 14.63) were randomized at 1:1 to undergo PCB (n = 20) or high-pressure balloon (HPB; n = 20) angioplasty of dysfunctional AVFs. There were no significant differences in baseline demographics between groups. Enrollment required a clinical diagnosis of a dysfunctional AVF attributed to a single stenotic lesion verified with digital subtraction angiography. Primary endpoints included device success, anatomic success, clinical success, and target lesion revascularization (TLR)-free survival. Secondary endpoints included dialysis circuit primary patency and procedure-related complication rates.

RESULTS

Device success rates were 100% in the HPB group and 35% in the PCB group (P < 0001): further dilation with an HPB was needed to achieve anatomic success in 13 of 20 cases in the PCB group (65%). Anatomic and clinical success rates were 100% in both groups. TLR-free survival (PCB, 308 d; HPB, 161 d; hazard ratio [HR], 0.478; 95% confidence interval [CI], 0.236-0.966; P = .03) and access circuit primary patency (PCB, 270 d; HPB, 161 d; HR, 0.479; 95% CI, 0.237-0.968; P = .04) were significantly in favor of PCB angioplasty. No minor or major procedure-related complications occurred.

CONCLUSIONS

In this single-center study, the use of PCBs resulted in superior TLR-free survival and dialysis access circuit primary patency of dysfunctional AVFs. However, additional HPB postdilation was required in the majority of cases.

Percutaneous transluminal angioplasty for dysfunctional femoral hemodialysis graft

PURPOSE

We aimed to evaluate the safety and effectiveness of percutaneous transluminal angioplasty (PTA) for dysfunctional femoral arteriovenous graft and analyze clinical or anatomic predictors of graft patency.

METHODS

The records of 45 patients who underwent PTA or thromboaspiration for dysfunctional or thrombosed femoral arteriovenous graft from 2005 to 2012 were reviewed retrospectively. Primary and secondary patency rates were determined at three, six, and 12 months after PTA. The primary patency rate was analyzed according to the presence of diabetes mellitus, graft age from the time of creation to the first intervention (<12 months or ≥12 months), presence of thrombus, shape of graft (U-shape vs. straight-shape), anastomosis type of graft (femoral-femoral vs. femoral-saphenous), location of stenosis (central vs. peripheral), length of stenosis (<2 cm vs. ≥2 cm), degree of stenosis severity (<70% vs. ≥70%), and stent insertion.

RESULTS

A total of 124 PTAs were performed in 45 patients. The primary patency rate at three, six, and 12 months was 84.8%, 63.6%, and 24.2%, respectively. The secondary patency rate at three, six, and 12 months was 95.2%, 95.2%, and 85.7%, respectively. The mean duration of primary and secondary patency was 13.2 and 35.7 months, respectively. No significant clinical or anatomical predictors of primary patency could be identified. Stent placement had a negative effect on primary patency.

CONCLUSION

PTA is a safe and effective treatment for dysfunctional femoral arteriovenous grafts. Stent placement seems to improve technical success, but does not enhance the primary patency rate of dysfunctional femoral arteriovenous grafts.

Drug-Eluting Balloon for the Treatment of Failing Hemodialytic Radiocephalic Arteriovenous Fistulas: Our Experience in the Treatment of Juxta-Anastomotic Stenoses

Purpose

The purpose of this article is to report our experience with drug-eluting balloons for the treatment of juxta-anastomotic stenoses of failing radiocephalic hemodialytic arteriovenous shunt and to evaluate the primary and secondary patency (PP and SP).

Methods

After approval by the local hospital's Ethical and Scientific Review Board, 26 consecutive patients with juxta-anastomotic stenosis of radiocephalic hemodialytic shunt were treated with angioplasty with drug-eluting balloon. The main objective was to evaluate PP defined, in accordance with the Kidney Disease Outcomes Quality Initiative recommendation, as the absence of dysfunction of the vascular access, patent lesion or residual stenosis <30% and no need for further reintervention of the target lesion (TL). PP and SP at 6, 12 and 24 months were evaluated, with echo color doppler and phlebography, for both arteriovenous fistulae, defined as absolute, and TL.

Results

Immediate postprocedural technical and clinical success was 100% for all the patients; we had only one technical failure in repeated treatments. At 6 months the absolute and TL PP was 96.1%; at 12 months the absolute PP was 81.8%, TL PP 90.9%, absolute SP 95.4%, TL SP 100%; at 24 months the absolute and TL PP was 57.8%; absolute and TL SP 94.7%; only one arteriovenous fistula was lost during the period.

Conclusions

The use of drug-eluting balloons, after standard angioplasty, improves primary patency and decreases reinterventions of TL in juxta-anastomotic stenoses of failing native dialytic arteriovenous shunts.

The Eternal Tale of Dialysis Access Vessels and Restenosis: Are Drug-Eluting Balloons the Solution?

In dialysis access fistulas and grafts, percutaneous transluminal angioplasty (PTA) is frequently followed by restenosis development, which results in repeated periodical re-interventions. The technique of drug-eluting balloon (DEB) angioplasty has shown promising results in the treatment of femoropopliteal arteriosclerotic lesions. In contrast to arteriosclerotic arteries, dialysis access vessels host unfavorable hemodynamics due to the direct conduction of high-pressure fluid into a low-pressure system. Hence, the beneficial effect of DEB angioplasty may be limited in this system. However, a first prospective randomized trial on 40 patients with arteriovenous fistula or graft stenoses exhibited a significantly higher 6-month primary patency of the treated lesions after DEB angioplasty than after uncoated balloon angioplasty. Despite such a positive reference, general recommendations regarding the value of DEBs in dialysis access vessels cannot be considered as serious unless large randomized controlled trials have been performed.

Arteriovenous graft for hemodialysis, graft venous anastomosis closure - current state of knowledge. Minireview

Backround. The use of artificial vascular grafts (arteriovenous graft, AVG) is indicated in patients in hemodialysis programs if the subcutaneous venous bed is exhausted or unsuitable for arteriovenous fistula (AVF) creation. The native fistula should be the hemodialysis access of first choice: AVF has better results in terms of function and potential complications. However, the use of AVG is necessary in some patients. In these patients, extensive clinical examination, color duplex sonography and angiography should be performed prior to indication. The technique of graft implantation requires respect for geometric relations for the graft anastomoses to minimize the formation of intimal hyperplasia mainly on the venous anastomosis. The main complications of AVG are stenosis on the venous anastomosis (VAG), causing closure of graft and graft infection. The cumulative function of AVG is 59-90% in the first year and 50-82% in the second year. Arteriovenous graft stenosis leading to thrombosis is a major cause of complications in patients undergoing hemodialysis. The purpose of this review is to summarise current knowledge of the diagnostics and treatment of graft thrombosis and discuss the issue in combination with relevant publications via Pubmed database.

CONCLUSION

The most frequent cause of failure of AVG for hemodialysis is stenosis and closure by VAG. AVG closure can be addressed surgically, endovascularly (amenable to thrombectomy by radiological or surgical means) and by hybrid performance.

Hemodynamic Shear Stress and Endothelial Dysfunction in Hemodialysis Access

Surgically-created blood conduits used for chronic hemodialysis, including native arteriovenous fistulas (AVFs) and synthetic AV grafts (AVGs), are the lifeline for kidney failure patients. Unfortunately, each has its own limitations: AVFs often fail to mature to become useful for dialysis and AVGs often fail due to stenosis as a result of neointimal hyperplasia, which preferentially forms at the graft-venous anastomosis. No clinical therapies are currently available to significantly promote AVF maturation or prevent neointimal hyperplasia in AVGs. Central to devising strategies to solve these problems is a complete mechanistic understanding of the pathophysiological processes. The pathology of arteriovenous access problems is likely multi-factorial. This review focuses on the roles of fluid-wall shear stress (WSS) and endothelial cells (ECs). In arteriovenous access, shunting of arterial blood flow directly into the vein drastically alters the hemodynamics in the vein. These hemodynamic changes are likely major contributors to non-maturation of an AVF vein and/or formation of neointimal hyperplasia at the venous anastomosis of an AVG. ECs separate blood from other vascular wall cells and also influence the phenotype of these other cells. In arteriovenous access, the responses of ECs to aberrant WSS may subsequently lead to AVF non-maturation and/or AVG stenosis. This review provides an overview of the methods for characterizing blood flow and calculating WSS in arteriovenous access and discusses EC responses to arteriovenous hemodynamics. This review also discusses the role of WSS in the pathology of arteriovenous access, as well as confounding factors that modulate the impact of WSS.

Endovascular techniques for cannulation difficulties in dialysis access

Although the arteriovenous fistula (AVF) is the access of choice for dialysis, its success as an access is limited by its high rate of failing to mature and its development of venous stenoses. This makes cannulation difficult or even impossible for dialysis staff. A variety of endovascular techniques exist for improving cannulation rates in AVFs. These include coil embolization of tributaries and balloon-assisted maturation in immature fistulae and fistuloplasty, stents and thrombus removal in mature failing access. This article aims to discuss the methods and evidence related to these techniques.

Treatment of hemodialysis vascular access arteriovenous graft failure by percutaneous intervention

A patent vascular access is the lifeline of end-stage renal disease patients depending on hemodialysis treatment. Once a functioning vascular access has been established, maintaining its patency is of utmost importance. During the last decades percutaneous techniques became increasingly important for the treatment of hemodialysis vascular access graft failure. In this review, the role of percutaneous balloon angioplasty and stent implantation is evaluated for different clinical scenarios, based on the available evidence.

Hybrid Simultaneous Treatment of Thrombosed Prosthetic Grafts for Hemodialysis

Purpose

The aim of the study was to evaluate our experience in the hybrid simultaneous treatment (open and endovascular) of acute thrombosis of prosthetic grafts for hemodialysis.

Methods

Between January 2011 and June 2013, 23 patients with acute thrombosis of a prosthetic graft for hemodialysis were urgently treated with a hybrid simultaneous treatment in order to obtain a prompt restoration of the flow. A new puncture of the graft was scheduled after 24 hours.

Results

Intraoperative technical success was 100% with a completion angiography showing the restored patency of the graft. As adjunctive procedures, in 6 patients (26.1%) locoregional thrombolysis was necessary and in all cases further endovascular manoeuvres (angioplasty/stenting) were immediately performed to solve a significant stenosis of the venous anastomosis/first tract of the vein. At 24 hours when the first puncture was done, three grafts were occluded resulting in a primary patency of 87%. During the follow-up (mean duration 5.6 months) four reocclusions occurred. In-stent restenosis occurred in all patients undergone stenting. At 1 year the rates of primary patency, primary assisted patency and secondary patency were 58.7%, 78.3% and 87%, respectively.

Conclusions

In our series the combined simultaneous hybrid approach in urgency maximizes the use of different available techniques, which appeared to improve overall success rate to save a thrombosed graft for hemodialysis. The great difference showed between primary and primary assisted patency demonstrates the necessity of a close follow-up.

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.

Stent salvage of arteriovenous fistulas and grafts

OBJECTIVES

This study analyzes our experience using stents to salvage dysfunctional hemodialysis access sites at a single institution.

METHODS

We examined the outcomes of 42 consecutive patients who had covered (36 patients) or bare-metal (9 patients) stent intervention for hemodialysis access salvage.

RESULTS

Of our 42 male patients, 11 had stent salvage of an arteriovenous fistula, which yielded postintervention primary and secondary 6-month patencies of 27% and 55%, respectively. For 31 patients with arteriovenous grafts, the postintervention primary and secondary 6-month patencies were 26% and 29%, respectively. Patency rates were superior for stents placed in patent access sites, in fistulas compared to grafts, and when stents were placed in forearm sites although only the latter achieved statistical significance.

CONCLUSIONS

Stents can extend patency for the thrombosed or failing arteriovenous access, but results are poor once thrombosis has occurred. Stent placement appears to be more effective in fistulas compared to grafts.

Effect of the time to intervention on the outcome of thrombosed dialysis access grafts managed percutaneously

PURPOSE

We aimed to investigate the effect of the time interval from the clinical presentation of a thrombosed dialysis access graft to intervention on procedure success.

MATERIALS AND METHODS

Records from two academic institutions for patients who underwent percutaneous thrombectomy of occluded surgical hemodialysis graft access sites in interventional radiology from 2006 to 2011 were reviewed retrospectively. The following data were recorded: gender, age, time and date of the initial request for a thrombectomy and the procedure, age of the surgical access, angiographic outcome, and clinical outcome (successful or unsuccessful postinterventional dialysis). Univariate and multivariate logistic regression were used to evaluate whether the time to intervention significantly affected the study endpoint.

RESULTS

In total, 268 percutaneous thrombectomies were performed in 139 patients. Of these 224 (83.5%) were categorized as successful and 44 (16.4%) as unsuccessful. The time to intervention was 19.9±30.1 vs. 22±35 hours for successful and unsuccessful procedures, respectively. The difference between the two was not significant, and there were also no significant differences in covariate distributions between successful and unsuccessful outcomes.

CONCLUSION

During the first 72 hours following clinical presentation of a thrombosed dialysis access graft, time to intervention may be considered independent of procedure outcome.

Percutaneous interventions in failing "necklace" hemodialysis grafts: long-term outcomes

PURPOSE

To determine primary and secondary patency after percutaneous interventions for malfunctioning anterior chest wall ("necklace") arteriovenous grafts (AVGs) for hemodialysis.

MATERIALS AND METHODS

Records of six consecutive patients with subclavian artery-to-contralateral subclavian vein necklace AVGs were reviewed. Patients underwent 34 procedures, including 28 balloon angioplasties, 24 pharmacomechanical thrombolyses, and six stent placements. Patency intervals after graft placement and after first intervention were calculated.

RESULTS

After 3 months, primary and secondary patency rates were 33% (two of six grafts) and 67% (four of six grafts), respectively. At 12 months, primary and secondary patency rates were 17% (one of six grafts) and 50% (three of six grafts), respectively. Median and mean primary patency times were 49 and 374 days, and median and mean secondary patency times were 293 and 575 days, respectively. The anatomic success rate of percutaneous interventions in malfunctioning AVGs was 97% (33 of 34 cases). At 3 years after implantation, the graft patency rate was 57% (four of seven grafts).

CONCLUSIONS

Percutaneous interventions were effective at maintaining patency in failing necklace AVGs. However, their primary and secondary patency were inferior to those cited in extremity AVG guidelines set forth by the Society of Interventional Radiology.

Measurement of vessel diameter during angioplasty: are we accurately performing this task?

Vessel diameter is objectively measured by a lead ruler positioned in the fluoroscopic field and software calibration during angioplasty. We conducted a prospective study to evaluate the accuracy of lead ruler determination of vessel diameter. Chronic hemodialysis patients undergoing an angioplasty procedure were included in this study (n = 37). Vessel diameter was determined by calibrating the fluoroscopy machine to a ruler with lead markers placed in the fluoroscopic field. The same calibration was used to measure the fully effaced angioplasty balloon in its intravascular location. We compared the measured balloon diameter with the actual (manufacturer's) diameter. The approximate depth of the ruler from the measured vessel was also determined. Angioplasty balloons appeared 13.75-40.83% (mean 25.8% ± 7.015) smaller than the actual size of the balloon (p < 0.0001) when measured using a calibrated fluoroscopic machine. There was a tendency toward the fact that the bigger the distance between the ruler and the vessel (that contained the angioplasty balloon), the more likely the technique underestimated the size of the angioplasty balloon. Lead ruler method underestimates the diameter of the vessel. Recognizing such a discrepancy is important when determining the size of an angioplasty balloon or endovascular stent.

Novel therapies for hemodialysis vascular access dysfunction: myth or reality?

Hemodialysis vascular access dysfunction is a major source of morbidity for patients with ESRD. Development of effective approaches to prevent and treat vascular access failure requires an understanding of the underlying mechanisms, suitable models for preclinical testing, systems for targeted delivery of interventions to maximize efficacy and minimize toxicity, and rigorous clinical trials that use appropriate outcome measures. This article reviews the substantial progress and ongoing challenges in developing novel treatments for arteriovenous vascular access failure and focuses on localized rather than systemic interventions.

Adventitial transduction of lentivirus-shRNA-VEGF-A in arteriovenous fistula reduces venous stenosis formation

Venous neointimal hyperplasia (VNH) causes hemodialysis vascular access failure. Here we tested whether VNH formation occurs in part due to local vessel hypoxia caused by surgical trauma to the vasa vasorum of the outflow vein at the time of arteriovenous fistula placement. Selective targeting of the adventitia of the outflow vein at the time of fistula creation was performed using a lentivirus-delivered small-hairpin RNA that inhibits VEGF-A expression. This resulted in significant increase in mean lumen vessel area, decreased media/adventitia area, and decreased constrictive remodeling with a significant increase in apoptosis (increase in caspase 3 activity and TUNEL staining) accompanied with decreased cellular proliferation and hypoxia-inducible factor-1α at the outflow vein. There was significant decrease in cells staining positive for α-smooth muscle actin (a myofibroblast marker) and VEGFR-1 expression with a decrease in MMP-2 and MMP-9. These results were confirmed in animals that were treated with humanized monoclonal antibody to VEGF-A with similar results. Since hypoxia can cause fibroblast to differentiate into myofibroblasts, we silenced VEGF-A gene expression in fibroblasts and subjected them to hypoxia. This decreased myofibroblast production, cellular proliferation, cell invasion, MMP-2 activity, and increased caspase 3. Thus, VEGF-A reduction at the time of arteriovenous fistula placement results in increased positive vascular remodeling.

Stent grafts for central venous occlusive disease in patients with ipsilateral hemodialysis access

PURPOSE

To assess long-term outcomes of stent grafts in patients with symptomatic central venous stenoses and occlusions ipsilateral to hemodialysis grafts or fistulas.

MATERIALS AND METHODS

The study included 52 of 55 consecutive patients with symptomatic stenoses of the central veins draining upper limb dialysis access grafts or fistulas treated with stent grafts. Indications for stent grafts were poor angioplasty results, rapid recurrence, or total occlusion. Endpoints were lesion patency and access patency following intervention. Mean follow-up was 25 months with a median of 24 months and 1.25 additional procedures per patient year. Patency rates were calculated using Kaplan-Meier analysis.

RESULTS

All stent grafts were successfully deployed. The lesion patency rates at 6, 12, 24, and 36 months after intervention were 60%, 40%, 28%, and 28%. The access patency rates at 6, 12, 24, and 36 months after intervention were 96%, 94%, 85%, and 72%. There was one major complication and no minor complications. In 40 patients (77%), the internal jugular vein confluence was covered by the stent graft. In five patients, the dialysis circuits became occluded, with no clinical sequelae in four; one patient was lost to follow-up. The contralateral brachiocephalic vein was covered in three patients (6%), preventing contralateral access construction in one patient.

CONCLUSIONS

Central vein stent graft placement in patients with hemodialysis access is associated with prolonged access patency. Coverage of major vein confluences, which occurred in 83% of the patients in this series, can compromise future access and should be avoided whenever possible by careful technique.

Challenges and management of high-flow arteriovenous fistulae

The Kidney Dialysis Outcomes Quality Initiative and Fistula First Initiative have embraced the arteriovenous fistula as the gold standard for hemodialysis accesses. Despite this status, fistulae are fraught with complex issues ranging from a high primary failure rate to high flow resulting in increased cardiovascular morbidity. It is important not to overlook the insidious peril of a hyperfunctioning access that may actively promote cardiac overload, cardiopulmonary recirculation, rapid access growth with aneurysm enlargement, recurrent venous stenosis resulting in access failure, and inflow/outflow mismatch. Once recognized, flow can and should be reduced to mitigate these and other negative effects.