Vascular Access Stenosis Research Articles

Hemodialysis vascular access stenosis detection using auditory spectro-temporal features of phonoangiography.

For end-stage renal disease patients undergoing hemodialysis, thrombosis caused by stenosis hinders the long-term use of vascular access. However, traditional spectral bruit analysis techniques for detecting the severity of vascular access stenosis are not robust. Accordingly, the present study proposes an automated method for mimicking a trained practitioner in performing the auscultation process. In the proposed approach, the bruit obtained using a standard phonoangiographic method is transformed into the time-frequency domain, and two spectro-temporal features, namely the auditory spectrum flux and the auditory spectral centroid, are then extracted. The distributions of the two features are analyzed using a multivariate Gaussian distribution (MGD) model. Finally, the distribution parameters of the MGD model are used to detect the presence (or otherwise) of vascular access stenosis. The validity of the proposed approach is investigated using the phonoangiography signals obtained from 16 hemodialysis patients with straight arteriovenous grafts over the upper arm region. The results show that the MGD covariance matrix coefficient of the auditory spectral centroid feature yields an accuracy of 83.87% in detecting significant vascular access stenosis. Thus, the proposed method has significant potential for the applications of vascular access stenosis detection.

A Meta-analysis of Stent Placement vs. Angioplasty for Dialysis Vascular Access Stenosis.

Dysfunction of arteriovenous fistulas (AVF) and arteriovenous grafts (AVG) contribute significantly to morbidity and hospitalization in the dialysis population. Despite advances in endovascular techniques, the incidence of vascular access stenosis remains problematic. Currently, the role of endovascular stent placement in the treatment of vascular access stenosis is poorly defined. This meta-analysis compares the primary patency rates of stenotic vascular access treated with stent placement vs. angioplasty. We searched Medline for English language publications from 1980 through December 2013, along with national conference proceedings and reference lists of all included publications. Inclusion criteria were a measure of primary patency, secondary patency, or access dysfunction. Studies were excluded if they were not in English or if they included pediatric patients. Ten studies with a total of 860 subjects met the inclusion criteria, including six experimental studies and four observational studies. There was significantly higher overall primary patency in those receiving stent placement than in those treated with angioplasty (pooled relative risk [RR]=0.79; 95% confidence interval [CI]: 0.65-0.96). The estimate did not differ by study design. The effect of treatment differed significantly (p=0.001) by the type of stents used, however. In studies including nitinol stents (six studies, 678 patients), 6-month patency was significantly better for stent placement than angioplasty (pooled RR=0.67; 95% CI: 0.54-0.84), whereas there was no significant differences between stent placement and angioplasty in those studies using bare metal stents exclusively (four studies, 182 patients; pooled RR=1.09; 95% CI: 0.91-1.32). There was significant heterogeneity between studies (I(2) =70.6%; p<0.0001). Our results suggest that stent placement may confer an advantage over balloon angioplasty in primary patency of dialysis access stenoses.

Clinical access assessment.

Vascular access guidelines recommend routine screening for the timely detection of stenosis using noninvasive methods, including clinical assessment (monitoring) and device-based surveillance relying on access blood flow (Qa) and static intra-access pressure (sVPR, static venous pressure ratio) measurements and duplex ultrasound (DU). We reviewed the literature to see how monitoring compares with surveillance in terms of compliance with the World Health Organization's criteria for screening tests. The fundamental element of monitoring, physical examination (PE), has a fair-to-good performance in detecting stenosis in both fistulas and grafts, similar to the Qa criteria recommended in the guidelines. In fistulas, the "or" combination of a positive PE with a Qa <900 mL/min or sVPR >0.5 is more sensitive in detecting stenosis (in up to 98% of cases), making it as good as DU. In grafts, PE performed significantly less well in diagnosing stenosis than sVPR or DU.In randomized controlled trials on fistulas, Qa surveillance enables a significant halving of the risk of thrombosis and access loss by comparison with monitoring alone when Qa criteria highly sensitive to stenosis are considered. In grafts, neither Qa nor DU nor sVPR is able to reduce thrombosis or access loss rates by comparison with monitoring alone. Our analysis indicates that regular monitoring should be the backbone of any vascular access stenosis screening program (possibly associated with Qa and sVPR surveillance for fistulas), and PE should be part of every teaching program for caregivers involved in hemodialysis.

Diagnostic Accuracy of Computer Tomography Angiography and Magnetic Resonance Angiography in the Stenosis Detection of Autologuous Hemodialysis Access: A Meta-Analysis

PurposeTo compare the diagnostic performances of computer tomography angiography (CTA) and magnetic resonance angiography (MRA) for detection and assessment of stenosis in patients with autologuous hemodialysis access.Materials and MethodsSearch of PubMed, MEDLINE, EMBASE and Cochrane Library database from January 1984 to May 2013 for studies comparing CTA or MRA with DSA or surgery for autologuous hemodialysis access. Eligible studies were in English language, aimed to detect more than 50% stenosis or occlusion of autologuous vascular access in hemodialysis patients with CTA and MRA technology and provided sufficient data about diagnosis performance. Methodological quality was assessed by the Quality Assessment of Diagnostic Studies (QUADAS) instrument. Sensitivities (SEN), specificities (SPE), positive likelihood ratio (PLR), negative likelihood values (NLR), diagnostic odds ratio (DOR) and areas under the receiver operator characteristic curve (AUC) were pooled statistically. Potential threshold effect, heterogeneity and publication bias was evaluated. The clinical utility of CTA and MRA in detection of stenosis was also investigated.ResultSixteen eligible studies were included, with a total of 500 patients. Both CTA and MRA were accurate modality (sensitivity, 96.2% and 95.4%, respectively; specificity, 97.1 and 96.1%, respectively; DOR [diagnostic odds ratio], 393.69 and 211.47, respectively) for hemodialysis vascular access. No significant difference was detected between the diagnostic performance of CTA (AUC, 0.988) and MRA (AUC, 0.982). Meta-regression analyses and subgroup analyses revealed no statistical difference. The Deek’s funnel plots suggested a publication bias.ConclusionDiagnostic performance of CTA and MRA for detecting stenosis of hemodialysis vascular access had no statistical difference. Both techniques may function as an alternative or an important complement to conventional digital subtraction angiography (DSA) and may be able to help guide medical management.

Juxta-anastomotic stenosis of native vascular access: prospective study of surgical treatment versus angioplasty

treatment with better outcomes in juxtaanastomotic stenosis in native vascular access, Although evidence level is not high. Furthermore, recent studies show angioplasty (PTA) results with high permeability in assisted patency. There are few studies comparing both techniques, limited by small sample size and methodologically. The objective of this study is comparing both techniques with a representative sample in a prospective study in a single center. JUXTA-ANASTOMOTIC STENOSIS OF NATIVE VASCULAR ACCESS: PROSPECTIVE STUDY OF SURGICAL TREATMENT VERSUS ANGIOPLASTY

Vascular Access Surveillance: Time to End the Controversy

AbstractThe establishment and maintenance of permanent vascular access for hemodialysis patients are important clinical problems. Vascular access surveillance, currently mandated by the CMS, refers to the task of identifying and correcting an underlying vascular access stenosis to prolong vascular access patency and survival. While this premise makes intuitive sense, this article discusses the underlying evidence to support it, outlining disparate conclusions of clinical practice guidelines and a recent commentary by experts in vascular access.

Blood Monocyte Count May Be a Predictor of Vascular Access Failure in Hemodialysis Patients

It has been reported that an increase in the counts of white blood cells (WBC) and their subpopulations is an independent predictor of atherosclerotic events and mortality. On the other hand, vascular access (VA) stenosis is caused by a progressive development of neointimal hyperplasia. We examined the relationship between VA failure and counts of peripheral WBC and their subpopulations in hemodialysis (HD) patients. The study population consisted of 82 patients undergoing regular HD. Twenty-two patients, who were unstable, were excluded from the study. After one year, we examined the relationship between VA failure and the counts of peripheral WBC and their subpopulations. In the follow-up period, 21 patients had complicated VA failure. The counts of WBC, neutrophils, lymphocytes, eosinophils, and basophils did not show a significant difference, but a monocyte count of ≥ 400/μL was shown to indicate a high probability of VA failure. Logistic regression analysis revealed that monocyte count was an independent risk factor of VA failure. The peripheral blood monocyte count may be a predictor of VA failure in HD patients.

THE ANASTOMOTIC ANGLE DOES CHANGE THE DISTURBED FLOW PATTERNS IN END-TO-SIDE AVF FOR HAEMODIALYSIS

Native arteriovenous fistula (AVF) is the best choice to achieve the vascular access (VA) for haemodialysis (HD) [Ene-Iordache, 2011]. Despite technological advancements, today the VA still has significant early failure rates due to stenosis. VA stenosis is importantly related to the local disturbed flow, i.e. low and oscillating wall shear stress (WSS) that triggers intimal hyperplasia, a fibromuscular thickening of the vessel wall.

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

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. 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. 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. 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.

Five Years of Vascular Access Stenosis Surveillance by Blood Flow Rate Measurements during Hemodialysis Using the Delta-H Method

To report experience over five years of vascular access (VA) stenosis surveillance. We prospectively monitored the blood flow rate (QA) of 145 VA in 131 ESRD (age 62.6 ±13.5 y) patients (pts). QA measurement: within the first hour of the hemodialysis (HD) session by the Delta-H method using the Crit Line III Monitor. All VA with baseline QA < 700 mL/min or decreased > 20% from baseline over time met the positive evaluation (PE) criteria and were referred for angiography (AG) plus elective intervention if stenosis = 50%. We found 54 cases of PE in 47 VA; the AG was performed in 87% (47/54) cases of PE and most of them (43/47, positive predictive value: 91.5%) showed significant stenosis (mean degree 80.5 ±12.9%). Mean QA increased from 554.7±107.6 mL/min to 977.9 ± 359.9 mL/min just before versus after preventive intervention (P<.001). Without difference when comparing the highest QA reported before stenosis development (889.8 ± 409.5 mL/min) and the QA recorded just post-intervention (P=.18). Kt/V index: improved from 1.43 ± 0.22 to 1.49 ± 0.21 just before versus after intervention (P=.006). 1) The Delta-H technique is an accurate method for early diagnosis of VA stenosis and is useful in monitoring the hemodynamic effect of elective VA treatment. 2) After preventive intervention for stenosis, functional VA status is restored and HD delivery is improved.

Genetic Causation of Neointimal Hyperplasia in Hemodialysis Vascular Access Dysfunction

The major cause of hemodialysis vascular access failure is venous stenosis resulting from neointimal hyperplasia. Genetic factors have been shown to be associated with cardiovascular disease and peripheral vascular disease (PVD) in the general population. Genetic factors may also play an important role in vascular access stenosis and development of neointimal hyperplasia by affecting pathways that lead to inflammation, endothelial function, oxidative stress, and vascular smooth muscle proliferation. This review will discuss the role of genetics in understanding neointimal hyperplasia development in hemodialysis vascular access dysfunction and other disease processes with similar neointimal hyperplasia development such as coronary artery disease and PVD.

Efficacy of SMART Stent Placement for Salvage Angioplasty in Hemodialysis Patients with Recurrent Vascular Access Stenosis

Vascular access stenosis is a major complication in hemodialysis patients. We prospectively observed 50 patients in whom 50 nitinol shape-memory alloy-recoverable technology (SMART) stents were used as salvage therapy for recurrent peripheral venous stenosis. Twenty-five stents each were deployed in native arteriovenous fistula (AVF) and synthetic arteriovenous polyurethane graft (AVG) cases. Vascular access patency rates were calculated by Kaplan-Meier analysis. The primary patency rates in AVF versus AVG at 3, 6, and 12 months were 80.3% versus 75.6%, 64.9% versus 28.3%, and 32.3% versus 18.9%, respectively. The secondary patency rates in AVF versus AVG at 3, 6, and 12 months were 88.5% versus 75.5%, 82.6% versus 61.8%, and 74.4% versus 61.8%, respectively. Although there were no statistically significant difference in patency between AVF and AVG, AVG showed poor tendency in primary and secondary patency. The usefulness of SMART stents was limited in a short period of time in hemodialysis patients with recurrent vascular access stenosis.

Potential Role of Recombinant Erythropoietin and Intravenous Iron Preparations in Target Vessel Re-Stenosis Following Coronary Stint Insertions in Hemodialysis Patients

LETTERS TO THE EDITOR Potential Role of Recombinant Erythropoietin and Intravenous Iron Preparations in Target Ves- sel Re-Stenosis Following Coronary Stint Inser- tions in Hemodialysis Patients Key words: ESRD, atherosclerosis, cardiovascular disease, anemia, oxidative stress, inflammation (Intern Med 50: 1449-1450, 2011) (DOI: 10.2169/internalmedicine.50.5173) To the Editor In an article published in the November is- sue of the Journal, Dr. Takeuchi and colleagues (1) reported on the incidence of target lesion re-stenosis in a cohort of 165 consecutive patients with coronary artery disease who had undergone 231 paclitaxel-eluting stent placements in their facility between May 2007 and August 2009. All pa- tients had been treated with two types of anti-platelet agents (aspirin and Clopidogrel or Ticlopidine) and 90% of the subjects had received follow-up coronary angiogram 6 months later. The underlying diseases in the study popula- tion included hypertension in 75%, hyperlipidemia in 78%, diabetes mellitus in 60% and end-stage renal disease treated with intermittent hemodialysis in 14%. Overall target lesion revascularization rate within 6 months following stent place- ment was 14.6%. The rate of target lesion re-stenosis in hemodialysis patients (43%) was far greater (p=0.0001, odds ratio: 6.61, 95% C.I.: 2.34-18.6) than in those with hyper- tension (15.0%), hyperlipidemia (12.4%), and diabetes mel- litus, treated with either oral medications (12.5%) or insulin (12.0%). Based on these observations the authors concluded that hemodialysis confers the greatest risk of target lesion re-stenosis after a coronary artery drug-eluting stint place- ment procedure. In fact comparison of outcomes among pa- tients with chronic kidney disease undergoing coronary ar- tery stint placement has revealed a significantly greater inci- dence of target vessel revascularization in the dialysis than in non-dialysis patients (2-5). The increased risk of target le- sion re-stenosis in hemodialysis patients has been attributed to chronic vascular inflammation and poor vessel dila- tion (6) due to medial calcification commonly present in these patients (7-9). It is noteworthy however, that using in- travascular ultrasonography or angiography Takeuchi et al (1) found no difference in the minimal stent area or mini- mal stent lumen diameter between patients who did and those who did not experience target lesion re-stenosis, thus excluding technical factors such as poor dilation as the cause of increased risk of stint re-stenosis in their hemodialysis-dependent patients. Exposure of blood to artifi- cial surfaces such as tubing and dialyzer membrane, me- chanical stress induced by the roller pump and influx of im- purities from the dialysate compartment are known to result in activation of leukocytes and release of pro-inflammatory mediators in patients undergoing hemodialysis. The recur- rent hemodialysis-induced inflammatory response is thought to, in part, contribute to target vessel re-stenosis following stent placement by stimulating neo-intimal expansion in hemodialysis-dependent patients (10). The author wishes to suggest that two additional factors can, in part, contribute to the high incidence of target vessel re-stenosis in patients maintained on chronic hemodialysis treatment. These include recombinant erythropoietin prod- ucts collectively referred to as erythropoiesis-stimulating agents (ESAs) and intravenous iron preparations which are used to treat anemia in nearly all dialysis-dependent patients with end-stage renal disease. ESAs have been shown to cause vasoconstriction-dependent hypertension and vascular smooth muscle cell proliferation, increase endothelin, thromboxane and reactive oxygen species (ROS) production, reduce prostacyclin and nitric oxide generation and up- regulate vascular tissue rennin-angiotensin system (reviewed in Ref. (11, 12)). These effects of ESAs particularly when administered in high doses to overcome ESA-resistant ane- mia in highly inflamed patients can contribute to target ves- sel re-stenosis following coronary stint placement. In addi- tion, by stimulating platelet production, increasing platelet activity (via augmentation of platelet calcium signaling), raising E-selectin and P selectin expression and release of plasminogen activator inhibitor-1 and von Willebrand factor, ESAs can promote thrombosis (reviewed in Ref. (11-14)). Together via these non-erythropoietic actions, the use of ESAs in dialysis patients can, at least, in part, account for the observed high incidence of target vessel re-stenosis and thrombosis in this population. In fact, the use of these agents has been linked to vascular access stenosis and thrombosis in dialysis patients and to accelerated tumor growth and thrombotic complications in cancer pa- tients (15, 16). In addition to ESAs, intravenous iron preparations which are commonly used to replenish iron stores in hemodialysis patients can intensify oxidative stress, stimulate monocyte activation and adhesion and promote vascular remodel- ing (17, 18), events that can potentially facilitate target ves- sel re-stenosis following stint placement. Given the universal use of ESAs and intravenous iron preparations in dialysis-dependent ESRD patients and the well-known effects of these agents on vascular tissue and the blood coagulation system, careful assessment of the po- Division of Nephrology and Hypertension, University of California Irvine, USA Received for publication January 17, 2011; Accepted for publication March 23, 2011 Correspondence to Dr. Nosratola D. Vaziri, ndvaziri@uci.edu

Status of research in vascular access for dialysis

Vascular access issues impose a major financial burden to health care and can be associated with increased morbidity and mortality. In this context, strategies, guidelines and available published information become important tools for health-care facilities and workers. While published data form a sound basis of formulating clinical practice guidelines for vascular access (VA), quality of the medical information is critically important. This study investigates the current status of VA publications. A PubMed search was performed to capture all articles related to dialysis vascular access published from January 1997 to December 2009. The articles were categorized by publication type, study subject, year of publication and specialty of the authors. A total of 2260 articles from 60 medical journals were identified. Insignificant publications (letters/communications, n = 125) were excluded from the analysis. Therefore, 2135 articles formed the basis for analysis. Sixteen of the 60 journals routinely published on vascular access and generated 1747 articles [nephrology = 7 (publications = 782); radiology = 4 (publications = 333); surgery = 5 (publications = 486)], while 44/60 journals published scarcely and produced 388 articles over the 13-year period. Overall, 1213 (57%) of the articles were published by the direct involvement of nephrologists [nephrologists alone (n = 564); nephrologists in collaboration with others (n = 649)]. There were 1194 observational studies, 444 case reports/series, 375 review/editorials, 51 basic research, 12 meta-analyses and 59 randomized controlled trials published over the 13-year period. The average impact factor for nephrology, radiology and surgery journals that routinely published on vascular access was 4.425, 3.099 and 2.679, respectively. Despite an increased rate of scholarly activity in the area of vascular access, there remains a significant challenge ahead due to the lack of randomized controlled trials and research focusing on the biology of vascular access stenosis.

Experimental Study of a New Method for Early Detection of Vascular Access Stenoses: Pulse Pressure Analysis at Hemodialysis Needle

Hemodialysis vascular access (VA) stenosis remains a frequent complication. However, early detection is challenging and costly. The aim of this in vitro study was to assess a new detection method based on pulse pressure analysis at the hemodialysis needle. A silicon model of a radiocephalic arteriovenous fistula was built in a mock loop. Pressure profiles were measured at the arterial hemodialysis needle and in the proximal feeding artery. Stenoses (50 and 25% diameter reduction) were created proximal to the anastomosis (proximal artery) and distal to the arterial needle (distal vein and proximal vein). The pulse pressure (PP) at the needle was divided by the PP at the feeding artery to obtain a dimensionless ratio, %PP. Experiments were conducted at different blood flow (500-1200 mL/min) and heart rates (60-90 beats/min) to test this new index over a wide range of hemodynamic conditions. In the control model (no stenosis), %PP was 20.26 +/- 4.55. A proximal artery 50% stenosis significantly decreased %PP to 7.69 +/- 2.08 (P < 0.0001), while the presence of 50% stenosis in the distal (36.20 +/- 2.12) and proximal (32.38 +/- 2.17) vein led to significantly higher values of %PP (P < 0.0001). For stenosis of 25% diameter reduction in the proximal artery, the %PP decreased to 15.45 +/- 2.13 (P = 0.0022) and the %PP increased with a 25% stenosis in the distal vein to 26.71 +/- 3.01 (P = 0.0003) and in the proximal vein to 26.53 +/- 2.67 (P = 0.0004). This in vitro study shows that the analysis of the PP at the dialysis needle is useful for early detection and localization of hemodialysis VA stenosis, independent of heart rate and flow level.

Use of enoxaparin to diminish the incidence of vascular access stenosis/thrombosis in chronic hemodialysis patients

Enoxaparin, a low molecular weight heparin, has been shown to be a safe and effective anticoagulant to prevent clotting in the extracorporeal circulation during hemodialysis. Enoxaparin also possesses antiproliferative properties, and reduces neointimal proliferation following vascular injury in animals. Use of enoxaparin during hemodialysis may be associated with decreased myointimal proliferation and diminished vascular access stenosis or failure. The aim of our study was to test the efficacy of enoxaparin to reduce the incidence of recurrent vascular access stenosis in chronic hemodialysis patients. Twenty-nine hemodialysis patients who suffered from recurrent arteriovenous (A-V) access stenosis were studied retrospectively to compare the incidence of vascular access procedures before and during enoxaparin administration. Enoxaparin was administered intravenously as a single bolus at the start of hemodialysis. Twenty-eight patients (14 male) were analyzed. Ten required a new fistula during the study period. Observed treatment times (years/patient) were 1.20 ± 0.87 for unfractionated heparin (UFH) and 3.04 ± 2.19 for enoxaparin (P = 0.0001). Angiographic procedure rates (procedures/year) were 1.76 ± 0.92 in the UFH group and 1.30 ± 1.01 in the enoxoparin group (P = 0.0786). There were no significant differences in time to first stenosis between the two groups (P = 0.5315). One patient receiving enoxaparin developed upper gastrointestinal bleeding and a second patient sustained a subdural hematoma after a fall. Our study demonstrated a trend toward a decreased number of angiographic procedures for maintaining A-V access patency in selected chronic hemodialysis patients treated with enoxaparin in comparison with UFH as anticoagulant during dialysis.

Early Vascular Access Blood Flow as a Predictor of Long-term Vascular Access Patency in Incident Hemodialysis Patients

The long-term clinical benefits of vascular access blood flow (VABF) measurements in hemodialysis (HD) patients have been controversial. We evaluated whether early VABF may predict long-term vascular access (VA) patency in incident HD patients. We enrolled 57 patients, of whom 27 were starting HD with arteriovenous fistulas (AVFs) and 30 with arteriovenous grafts (AVGs). The patients' VABF was measured monthly with the ultrasound dilution technique over the course of the first six months after the VA operation. During the 20.4-month observational period, a total of 40 VA events in 23 patients were documented. The new VA events included 13 cases of stenosis and 10 thrombotic events. The lowest quartile of average early VABF was related to the new VA events. After adjusting for covariates such as gender, age, hypertension, diabetes, VA type, hemoglobin levels, body mass index, parathyroid hormone, and calcium-phosphorus product levels, the hazard ratio of VABF (defined as <853 mL/min in AVF or <830 mL/min in AVG) to incident VA was 3.077 (95% confidence interval, 1.127-8.395; P=0.028). There were no significant relationships between early VABF parameters and VA thrombosis. It is concluded that early VABF may predict long-term VA patency, particularly VA stenosis.

Accuracy of Ultrasound in the Detection of Inflow Stenosis of Arteriovenous Fistulae: Results of a Prospective Study

While vascular ultrasound (US) has been highlighted to detect vascular access stenosis, its accuracy in the identification of inflow stenosis (IS) (anastomosis and/or juxta-anastomotic area) compared with the gold standard (angiography) has not been evaluated. One hundred three consecutive fistulae referred for interventions were included in this study. Preprocedure US of inflow segment was performed. Angiography from the feeding artery to the right atrium was then conducted. US comparison to angiography in the detection of IS (anastomosis and/or juxta-anastomotic area) was evaluated. Additionally, comparison of US to angiography in the assessment of juxta-anastomotic and anastomotic stenosis was reported separately. Data from 103 patients were available for analysis. Overall, US was negative for IS in 52 cases. Of these, 47 did not show a lesion on angiography. Only five cases demonstrated a stenosis on angiography. Fifty-one cases had IS by US, 50 were confirmed by angiography while one case did not show a lesion on angiography. Consequently, US had a sensitivity of 91%, specificity of 98%, and positive and negative predictive values were 98% and 90%, respectively. The sensitivity, specificity, negative, and positive predictive values for juxta-anastomotic and anastomotic lesions evaluated separately were 92%, 98%, 92%, 98% and 79%, 100%, 95%, 100%, respectively. Linear regression analysis showed a significant positive correlation between US and angiography for anastomotic (r2=0.71, p<0.0001; slope=0.63+/-0.098 and intercept=24+/-6) and juxta-anastomotic stenosis (r2=0.71, p<0.0001; slope=0.68+/-0.060 and intercept=23+/-4). These results reveal that US has a high degree of accuracy in the detection of IS.

Effect of Dipyridamole Plus Aspirin on Hemodialysis Graft Patency

Conclusion: Use of the combination of dipyridamole plus aspirin reduces risk of stenosis and improves duration of primary unassisted patency of newly created arteriovenous grafts. Summary: Arteriovenous grafts remain a common source for dialysis access. Although it is generally possible to restore patency to arteriovenous grafts after thrombosis, such procedures are costly. The annual cost of procedures related to vascular access is estimated to exceed $1 billion in the United States (US Renal Data System. 2007 Annual data report: atlas of end-stage renal disease in the United States. Bethesda, MD: National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, 2007). It is postulated that because dipyridamole acts by inhibiting the proliferation of vascular smooth muscle cells and that its use in treatment of patients with newly created hemodialysis access may improve patency of the dialysis access graft. The authors therefore performed a randomized, double-blind, placebo-controlled trial to determine whether extended-release dipyridamole plus aspirin inhibited stenosis of vascular access and prolonged primary unassisted patency of newly created dialysis access grafts. Patients were randomized to receive dipyridamole at a dose of 200 mg and aspirin at a dose of 25 mg twice daily, or placebo, after placement of a new arteriovenous dialysis access graft. The primary outcome was loss of primary unassisted patency of the access graft. Secondary outcomes included cumulative graft failure and death. Thirteen centers in the United States participated in the study, and 649 patients were randomly assigned to receive dipyridamole plus aspirin (321 patients) or placebo (328 patients). The study extended for 4.5 years, with an additional 6 months of follow-up. Blood flow rates at access sites were measured each month after the patient started on hemodialysis. Measurements were done using ultrasound-indicated dilution techniques. Baseline characteristics of the two study groups were similar, as were graft blood flow rates at the time of baseline measurement. Of the grafts placed, 94% were expanded polytetrafluoroethylene, and 5% were made from some other synthetic materials. Twenty-nine percent of the grafts were forearm grafts and 44% were in the upper arm, with 6% in the leg. The rate of adherence to the study medication regimen was 83% in both groups. At 1 year, primary unassisted patency was 23% (95% confidence interval [CI], 18%-28%) in the placebo group and 28% (95% CI, 23%-35%) in the dipyridamole-aspirin group. Adjusting for prespecified factors, the hazard ratio (HR) for loss of primary unassisted graft patency in the dipyridamole plus aspirin group compared with the placebo group was 0.82 (95% CI, 0.68-0.98; P = .03). This provided a relative reduction in the rate of loss of primary unassisted graft patency of 18%. The HR for loss of primary unassisted graft patency in the dipyridamole-aspirin group compared with the placebo group was 0.76 (95% CI, 0.60-0.96; P = .02) among patients not receiving aspirin at baseline and 0.92 (95% CI, 0.68-1.24; P = .57) among those receiving aspirin at baseline. There was an overall 28% reduction in rate of stenosis of >50% from treatment with dipyridamole plus aspirin (HR, 0.72; 95% CI, 0.57-0.90; P = .005). Mean duration of primary patency was 5.8 months (95% CI, 4.3-7.1) in the extended-release dipyridamole-aspirin group and 4.3 months (95% CI, 3.6-5.4) in the placebo group. Comment: The data indicate that the combination of extended release dipyridamole plus aspirin in patients who had not previously received aspirin therapy had a statistically significant effect on extending primary patency of hemodialysis access grafts. The effect was modest and not clinically important. The aspirin and dipyridamole combination delayed by 6 weeks the median time to loss of primary patency in patients with newly created arteriovenous grafts. Put another way, the drug combination provides a reduction in the number of patients with primary graft failure by one patient for every 20 patients treated for 1 year. Because treatment with dipyridamole plus aspirin can cost between $5000 and $2200 per year, it is unclear if this therapy is cost-effective. The importance of this study is that it indicates that pharmacologic therapy targeting intimal hyperplasia potentially can improve the patency of dialysis access grafts. However, a better, more robust, effect will be needed to change practice.

Stent Placement in Hemodialysis Access

Vascular access stenosis in patients undergoing chronic hemodialysis is a major issue that is associated with increased morbidity, mortality, and cost of medical care. Recent data have emphasized that endovascular stents could be used in the treatment of central as well as peripheral stenotic lesions. In general, a peripheral or central vein lesion that is elastic or recurs within a three-month period after an initially successful balloon angioplasty or a stenosis where surgical revision is not possible are some indications for intravascular stent placement. Recent reports have expanded the role of stents in the management of pseudoaneurysms associated with dialysis access. In this context, the utilization of these devices must take into account a fair comparison with the traditional (surgical) approaches regarding effectiveness as well as costs. This report describes the role of stents in arteriovenous dialysis access. In addition, some of the recent advances in the structure and complicating issues such as stent fracture, migration, and infection, as well cannulation through the stent, are discussed.