Percutaneous balloon cryoplasty: A new therapy for rapidly recurrent anastomotic venous stenoses of hemodialysis grafts?

Iatrogenic Fistula in Hemodialysis Patients: An Alternative Approach to Thrombectomy of Arteriovenous Graft (AVG) Thrombosis

Arterial venous (AV) fistula is the first choice of vascular access to perform hemodialysis in the vast majority of suitable patients followed by arteriovenous grafts (AVG). An iatrogenic fistula can occur when a second vein adjacent to the graft is punctured and the needle traverses the vein. In normal circumstances, this has no clinical repercussions and does not need correction, and in prior reports, it has helped to maintain the patency of partially occluded grafts but rarely can lead to thrombosis of the graft due to reduced flow and pressure in the graft lumen. We report here what we believe is a unique approach to perform thrombectomy of an occluded graft in a 71-year-old patient on hemodialysis to avoid placement of tunneled hemodialysis catheters and complications associated with catheters. When the outflow of basilic vein in this patient was thrombosed and could not be traversed, we successfully used an iatrogenic fistula as main outflow vein for the graft and created an alternative vein for drainage thus avoiding placement of a tunneled catheter for hemodialysis.

Hybrid salvage of thrombosed dialysis access grafts

BACKGROUND

To report our experience and evaluate the results of a hybrid procedure comprising of surgical thrombectomy and adjuvant high pressure balloon angioplasty for management of thrombosed arteriovenous grafts (AVGs) with underlying venous anastomotic stenosis.

METHODS

Between January 2015 and June 2017, 148 patients with first-time thrombosis of AVGs were considered for treatment with surgical thrombectomy followed by high pressure balloon angioplasty of the underlying venous anastomotic lesions. Monitoring and surveillance was subsequently performed using clinical and hemodialysis criteria to detect a failing/failed access. Primary, assisted primary, and secondary patency rates were calculated using Kaplan-Meier analysis.

RESULTS

This hybrid procedure was technically successful in 135 cases (91.2%) and clinically successful in 131 cases (88.5%). The postintervention primary patency rate of the target lesions was 68.2%, 52.4%, and 44.2% at 3, 6, and 12 months, respectively. Endovascular re-interventions increased significantly the postintervention assisted primary patency to 79.1%, 71.9%, and 66.8% (P=0.0004), and the postintervention secondary patency to 86.5%, 82.2%, and 78.6% (P<0.0001) at the same time points, respectively.

CONCLUSIONS

Hybrid salvage of thrombosed AVGs using high pressure balloon angioplasty of the venous anastomotic stenosis following surgical thrombectomy by Fogarty catheter is a highly successful and safe procedure, with acceptable short-term primary patency. The need for repeated interventions demonstrates the necessity of continuous graft monitoring and surveillance to improve both assisted primary, and secondary patency rates.

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.

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.

Superior Vena Cava Syndrome: Role of the Interventionalist

Superior vena cava syndrome results from the obstruction of blood flow through the superior vena cava and is most often due to thoracic malignancy. However, benign etiologies are on the rise secondary to more frequent use of intravascular devices such as central venous catheters and pacemakers. Although rarely a medical emergency, the symptoms can be alarming, particularly to the patient. Traditionally, superior vena cava syndrome has been managed with radiotherapy and chemotherapy. But interventional endovascular techniques have made inroads that offer a safe, rapid, and durable response. In many cases, it may be the only reasonable treatment. Because of this, an approach to endovascular treatment of this condition must be in the armamentarium of the interventional radiologist. This review will provide the reader with an insight into the etiology, pathophysiology, and various management principles of superior vena cava syndrome. The focus will be on understanding the techniques used during various endovascular interventions, including angioplasty, stenting, and pharmacomechanical thrombolysis. Discussion will also be centred on possible complications and current evidence as well as controversies regarding these approaches.

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.

Relationship between the Outcomes of Stent Placement and the Properties of Arteriovenous Graft Outflow Vein Stenotic Lesions

Purpose

The mechanisms of venous stenosis in vascular access include vascular constriction and neointimal hyperplasia. One purpose of this study was to examine the properties of stenotic lesions in arteriovenous graft outflow veins and the association with the results of treatment using stent placement.

Subjects and Methods.

The study involved 46 patients who underwent stent placement to treat arteriovenous graft outflow vein stenosis. The properties of stenotic lesions before stent placement were observed by ultrasonography and were classified into three groups: vascular constriction types, neointimal proliferation types, and mixed types. Stent placement was performed when elastic recoil occurred or when restenosis occurred at the same site within three months. The primary patency results for each group were then compared. The primary endpoint included patency of the treatment area.

Results.

The primary patency rate of the treatment area at 6, 12, 18 and 24 months post-stent placement for the vascular constriction type was 100.0%, 92.3%, 84.6% and 75.2%, respectively. Those rates were 66.7%, 33.3%, 33.3% and 25.0% for the neointimal proliferation type, and 90.5%, 52.4%, 38.1% and 27.2% with the mixed type. The vascular constriction type displayed excellent primary patency rates after stent placement.

Conclusions.

It is possible to define the types of stenotic lesions for which stent therapy is effective through morphological diagnosis of those lesions using ultrasound tomography.

Stent-Grafts Improve Secondary Patency of Failing Hemodialysis Grafts

Purpose

Failing hemodialysis grafts continue to pose a challenge in the care of patients with end-stage renal disease (ESRD). We review our experience using percutaneous stent-grafts for the treatment of venous outflow stenosis and occlusion in order to assess their efficacy in nonautologous graft salvage.

Methods

This is a retrospective review of patients treated with percutaneous Viabahn® stent-grafts for failing hemodialysis arteriovenous grafts (AVGs), between 6/2006 and 12/2009. All stent-grafts were deployed across the venous anastomosis to address the outflow obstruction. Patency and re-intervention rates were estimated using Kaplan-Meier analysis.

Results

Twenty patients had stent-grafts placed. Successful stent-grafting was defined as <30% residual stenosis and the ability to dialyze through the graft post-treatment. Technical success for stent-grafting was 100%. Median follow-up was 23 months (range 3 to 37 months). Stent-graft patency at 6 months: 94.7%, 12 months: 94.7%, 18 months: 82.1%, 24 months: 82.1%, 36 months: 82.1%. Freedom from re-intervention was 69% at 24 months and 50% at 36 months. Two AVGs failed and had to be removed without further interventions, because of complete occlusion and infection. Two patients (10%) required re-intervention for arterial inflow stenosis. One patient (5%) required balloon angioplasty and stenting of stenosis distal to the stent-graft. One patient (5%) developed in-stent stenosis and was treated with placement of a new stent. Graft salvage rate was 80% at 36 months.

Conclusions

Stent-grafts can be successfully used to improve freedom from re-intervention rates and overall patency rates of failing AVGs.

"Venopathy" at work: recasting neointimal hyperplasia in a new light

Hemodialysis vascular access is a unique form of vascular anastomosis. Although it is created in a unique disease state, it has much to offer in terms of insights into venous endothelial and anastomotic biology. The development of neointimal hyperplasia (NH) has been identified as a pathologic entity, decreasing the lifespan and effectiveness of hemodialysis vascular access. Subtle hints and new data suggest a contrary idea-that NH, to some extent an expected response, if controlled properly, may play a beneficial role in the promotion of maturation to a functional access. This review attempts to recast our understanding of NH and redefine research goals for an evolving discipline that focuses on a life-sustaining connection between an artery and vein.

Stent graft versus balloon angioplasty for failing dialysis-access grafts

BACKGROUND

The leading cause of failure of a prosthetic arteriovenous hemodialysis-access graft is venous anastomotic stenosis. Balloon angioplasty, the first-line therapy, has a tendency to lead to subsequent recoil and restenosis; however, no other therapies have yet proved to be more effective. This study was designed to compare conventional balloon angioplasty with an expanded polytetrafluoroethylene endovascular stent graft for revision of venous anastomotic stenosis in failing hemodialysis grafts.

METHODS

We conducted a prospective, multicenter trial, randomly assigning 190 patients who were undergoing hemodialysis and who had a venous anastomotic stenosis to undergo either balloon angioplasty alone or balloon angioplasty plus placement of the stent graft. Primary end points included patency of the treatment area and patency of the entire vascular access circuit.

RESULTS

At 6 months, the incidence of patency of the treatment area was significantly greater in the stent-graft group than in the balloon-angioplasty group (51% vs. 23%, P<0.001), as was the incidence of patency of the access circuit (38% vs. 20%, P=0.008). In addition, the incidence of freedom from subsequent interventions at 6 months was significantly greater in the stent-graft group than in the balloon-angioplasty group (32% vs. 16%, P=0.03 by the log-rank test and P=0.04 by the Wilcoxon rank-sum test). The incidence of binary restenosis at 6 months was greater in the balloon-angioplasty group than in the stent-graft group (78% vs. 28%, P<0.001). The incidences of adverse events at 6 months were equivalent in the two treatment groups, with the exception of restenosis, which occurred more frequently in the balloon-angioplasty group (P<0.001).

CONCLUSIONS

In this study, percutaneous revision of venous anastomotic stenosis in patients with a prosthetic hemodialysis graft was improved with the use of a stent graft, which appears to provide longer-term and superior patency and freedom from repeat interventions than standard balloon angioplasty. (ClinicalTrials.gov number, NCT00678249.)

Freeze-thaw induced biomechanical changes in arteries: role of collagen matrix and smooth muscle cells

Applications involving freeze-thaw, such as cryoplasty or cryopreservation can significantly alter artery biomechanics including an increase in physiological elastic modulus. Since artery biomechanics plays a significant role in hemodynamics, it is important to understand the mechanisms underlying these changes to be able to help control the biomechanical outcome post-treatments. Understanding of these mechanisms requires investigation of the freeze-thaw effect on arterial components (collagen, smooth muscle cells or SMCs), as well as the components' contribution to the overall artery biomechanics. To do this, isolated fresh swine arteries were subjected to thermal (freeze-thaw to -20 degrees C for 2 min or hyperthermia to 43 degrees C for 2 h) and osmotic (0.1-0.2 M mannitol) treatments; these treatments preferentially altered either the collagen matrix (hydration/stability) or smooth muscle cells (SMCs), respectively. Tissue dehydration, thermal stability and SMC functional changes were assessed from bulk weight measurements, analyses of the thermal denaturation profiles using Fourier transform infrared (FTIR) spectroscopy and in vitro arterial contraction/relaxation responses to norepinephrine (NE) and acetylcholine (AC), respectively. Additionally, Second Harmonic Generation (SHG) microscopy was performed on fresh and frozen-thawed arteries to directly visualize the changes in collagen matrix following freeze-thaw. Finally, the overall artery biomechanics was studied by assessing responses to uniaxial tensile testing. Freeze-thaw of arteries caused: (a) tissue dehydration (15% weight reduction), (b) increase in thermal stability (approximately 6.4 degrees C increase in denaturation onset temperature), (c) altered matrix arrangement observed using SHG and d) complete SMC destruction. While hyperthermia treatment also caused complete SMC destruction, no tissue dehydration was observed. On the other hand, while 0.2 M mannitol treatment significantly increased the thermal stability (approximately 4.8 degrees C increase in denaturation onset), 0.1 M mannitol treatment did not result in any significant change. Both 0.1 and 0.2 M treatments caused no change in SMC function. Finally, freeze-thaw (506+/-159 kPa), hyperthermia (268+/-132 kPa) and 0.2 M mannitol (304+/-125 kPa) treatments all caused significant increase in the physiological elastic modulus (Eartery) compared to control (185+/-92 kPa) with the freeze-thaw resulting in the highest modulus. These studies suggest that changes in collagen matrix arrangement due to dehydration as well as SMC destruction occurring during freeze-thaw are important mechanisms of freeze-thaw induced biomechanical changes.

Biological coating for arterial stents: the next evolutionary change in stents

PURPOSE

To describe the in vivo results of a promising new stent-graft lined with peritoneum.

METHODS

Eighteen dogs underwent balloon angioplasty injury to the bilateral iliac arteries followed by placement of either an 8-mm x 5-cm glutaraldehyde-fixed bovine peritoneum- lined balloon-expandable stent (PLS) or a similarly sized, commercially prepared, polyester-lined self-expanding stent (DLS) as a control. Animals were sacrificed at 1 and 6 months. Biplanar arteriography and intravascular ultrasound were done at the time of sacrifice, and the vessels were harvested after perfusion fixation for histology/morphometry. Immunofluorescence with CD34 and factor VIII staining was used to evaluate endothelialization, while alpha-actin was used to quantify smooth muscle cell (SMC) deposition.

RESULTS

At 1 month, all vessels were patent in both groups. At 6 months, 8 of 9 vessels were open in the PLS group versus 6 of 9 in the control DLS group. Vessel lumen diameter at 1 month was significantly greater in the PLS vessels compared to the DLS group at 1 cm above the stent (35.9 +/- 4.4 versus 29.4 +/- 4.7 mm2; p = 0.02) and 1 cm below the stent (37.2 +/- 7.1 versus 25.2 +/- 3.2 mm2; p = 0.005); these results persisted to 6 months. Histological morphometry demonstrated progression of neointimal hyperplasia in the DLS stent between 30 and 180 days (8.3 +/- 1.79 versus 14.9 +/- 6.6 mm2; p = 0.03), whereas the peritoneum-lined stent had no change during the same time period (4.62 +/- 0.98 versus 4.72 +/- 0.97 mm2; p = 0.85). The same patterns were true for the intima:media ratio. Immunohistochemistry demonstrated complete endothelialization at 6 months in both DLS and PLS. However, SMC staining with alpha-actin demonstrated more smooth muscle actin-positive cells in the DLS compared to the PLS (327 +/- 87 versus 262 +/- 73 counts/5 high-powered fields; p = 0.04).

CONCLUSION

Peritoneum-lined stents offer a novel method to improve patency of lower extremity arterial stents.

Hemodialysis vascular access dysfunction: a cellular and molecular viewpoint

Hemodialysis vascular access dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population. The major cause of hemodialysis vascular access dysfunction is venous stenosis as a result of neointimal hyperplasia. Despite the magnitude of the clinical problem, however, there has been a paucity of novel therapeutic interventions in this field. This is in marked contrast to a recent plethora of targeted interventions for the treatment of arterial neointimal hyperplasia after coronary angioplasty. The reasons for this are two-fold. First there has been a relative lack of cellular and molecular research that focuses on venous neointimal hyperplasia in the specific setting of hemodialysis vascular access. Second, there have been inadequate efforts by the nephrology community to translate the recent advances in molecular and interventional cardiology into therapies for hemodialysis vascular access. This review therefore (1) briefly examines the different forms of hemodialysis vascular access that are available, (2) describes the pathology and pathogenesis of hemodialysis vascular access dysfunction in both polytetrafluoroethylene grafts and native arteriovenous fistulae, (3) reviews recent concepts about the pathogenesis of vascular stenosis that could potentially be applied in the setting of hemodialysis vascular access dysfunction, (4) summarizes novel experimental and clinical therapies that could potentially be used in the setting of hemodialysis vascular access dysfunction, and, finally, (5) offers some broad guidelines for future innovative translational and clinical research in this area that hopefully will reduce the huge clinical morbidity and economic costs that are associated with this condition.