Inflow Stenoses in Dysfunctional Hemodialysis Access Fistulae and Grafts

Inflow Stenoses in Dysfunctional Hemodialysis Access Fistulae and Grafts Lucien E.M. Duijm, MD, PhD, Ylian S. Liem, MD, Rob H.H. van der Rijt, MD, Ferenc J. Nobrega, MD, Harrie C.M. van den Bosch, MD, Petra Douwes-Draaijer, MD, PhD, Philippe W.M. Cuypers, MD, PhD, and Alexander V. Tielbeek, MD, PhD ● Background: The aim of the study is to prospectively determine the incidence of inflow stenoses in dysfunctional hemodialysis access arteriovenous fistulae (AVFs) and grafts (AVGs). Methods: Contrast-enhanced magnetic resonance angiography (CE-MRA) was performed of 66 dysfunctional AVFs and 35 AVGs in 56 men and 45 women (mean age, 62 years; age range, 31 to 86 years). Complete inflow (from the subclavian artery), shunt region, and complete outflow (including subclavian vein) were shown at CE-MRA. In addition to standard digital subtraction angiography (DSA) of the shunt region and outflow, DSA of the complete inflow was obtained through access catheterization of all cases in which CE-MRA showed an inflow stenosis. Vascular stenosis is defined as greater than 50% decrease in luminal diameter compared with an uninvolved vascular segment located adjacent to the stenosis. Endovascular intervention of stenoses was performed in connection with DSA. Results: CE-MRA showed 19 arterial stenoses in 14 patients (14%). DSA confirmed 18 of these lesions in 13 patients and showed no additional inflow lesions. Of the 13 patients, 7 patients had arterial stenoses only and 6 patients had accompanying stenoses in the shunt region and/or outflow. Referral criteria for the 13 patients to undergo access evaluation had been decreased flow rates (9 patients), steal symptoms (2 patients), and insufficient access maturation (2 patients). Access flow of the 9 patients with a low-flow access improved from 477 ⴞ 74 mL/min to 825 ⴞ 199 mL/min after angioplasty. One patient with steal symptoms became symptom free after angioplasty. Endovascular intervention in 3 patients proved to be unsuccessful. Conclusion: Inflow stenoses are not uncommon in dysfunctional hemodialysis access shunts. We suggest that radiological evaluation comprise assessment of the complete arterial inflow. Am J Kidney Dis 48:98-105. © 2006 by the National Kidney Foundation, Inc. INDEX WORDS: Hemodialysis (HD); graft; fistula; stenosis; angiography; magnetic resonance angiography.

A

CCESS COMPLICATIONS are a major determinant of morbidity and multiple hospital admissions of patients receiving hemodialysis. The most common complications are the occurrence of maturation failure of an access and shunt failure caused by thrombosis, infection, or pseudoaneurysm formation.1,2 Access thrombosis usually is caused by the development of vascular stenoses, and early treatment of these stenoses by means of percutaneous intervention From the Departments of Radiology, Nephrology, and Vascular Surgery, Catharina Hospital, Eindhoven; and Departments of Epidemiology and Biostatistics and Radiology, Erasmus MC-University Medical Center Rotterdam, The Netherlands. Received December 28, 2005; accepted in revised form March 28, 2006. Originally published online as doi:10.1053/j.ajkd.2006.03.076 on May 19, 2006. Support: None. Potential conflicts of interest: None. Address reprint requests to Lucien E.M. Duijm, MD, PhD, Department of Radiology, Catharina Hospital, Michelangelolaan 2, 5623 EJ, Eindhoven, The Netherlands. E-mail: [email protected] © 2006 by the National Kidney Foundation, Inc. 0272-6386/06/4801-0011$32.00/0 doi:10.1053/j.ajkd.2006.03.076 98

or surgery may prolong shunt survival.3-5 The primary focus of upper-limb hemodialysis access intervention has been on the depiction and treatment of stenoses located at the anastomotic sites of arteriovenous fistulae (AVFs) and synthetic arteriovenous bridge grafts (AVGs) and stenoses located within the native outflow veins.6,7 However, stenosis formation may occur anywhere in the vascular tree of an access, which comprises the arterial inflow from the subclavian artery, the shunt region, and venous outflow up to the superior caval vein. The presence of stenoses on the arterial side is not discussed as frequently, but also is likely to compromise access function. Arterial stenosis probably is common in the hemodialysis population, many of whom have additional major risk factors for atherosclerotic disease, such as older age, diabetes mellitus, and hypertension. Stenosis on the arterial side has been reported to occur in 0% to 28% of patients, depending on patient population, definition of arterial stenosis, and degree of depiction of the arterial inflow.6,8-12 To date, the incidence of central arterial inflow stenoses remains unknown because the reported studies do not include proper assessment of central arterial inflow comprising

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the subclavian and axillary artery. The purpose of the current study is to prospectively determine the incidence of arterial stenoses in dysfunctional hemodialysis access fistulae and grafts. We performed digital subtraction angiography (DSA) of the complete vascular tree of shunts, including inflow from the subclavian artery, in all cases in which contrast-enhanced (CE) magnetic resonance (MR) angiography (MRA) of dysfunctional shunts showed an inflow stenosis. METHODS

Patient Population All long-term hemodialysis patients with permanent AVFs or AVGs who were referred to the interventional radiology department because of signs suggestive of shunt dysfunction were eligible to enter the study. Patients were allowed to be included only once during the study period. We excluded 8 patients who experienced acute access failure that required surgical or endovascular intervention within 24 hours; prompt scheduling and performance of CE-MRA was not feasible in these acute settings. The 8 cases included 4 patients who could not undergo hemodialysis because of sudden onset of insufficient access flow rate and 1 patient whose access was at risk after formation of a large hematoma after insertion of a hemodialysis needle. In 3 other patients, clinical examination suggested shunt occlusion, which was verified by using DSA. Patients who presented with contraindications for MRA also had to be excluded (claustrophobia, 7 patients; pacemaker, 2 patients). Two patients did not fit in the MR gantry because of obesity, and 4 patients did not want to participate in the study. Referral criteria included decreased flow rates measured with use of the Transonic HD01 system (Transonic, Ithaca, NY; access flow ⬍ 600 mL/min or flow rate ⬍ 1,000 mL/min that had decreased by ⬎ 25% at serial measurements; 68 patients), repeated problematic access cannulation (9 patients), frequent prolonged bleeding after cannulation (3 patients), steal symptoms (4 patients), elevated venous pressures (elevated venous pressures ⬎135 to 140 mm Hg on 3 consecutive hemodialysis treatments at a dialyzer flow rate of 200 mL/min; 11 patients), or insufficient access maturation (6 patients). Between February 1, 2002, and November 30, 2005, a total of 101 accesses (66 AVFs and 35 AVGs) in 56 men and 45 women (mean age, 62 years; age range, 31 to 86 years) were evaluated by using CE-MRA. Data for risk factors for peripheral arterial disease, causes of end-stage renal disease, and duration of hemodialysis therapy were retrieved from patient records of the nephrology department. The study was approved by our institutional review board.

Imaging Techniques MR angiography. All examinations were performed on a 1.5-T clinical scanner (ACS-NT; Philips Medical Systems, Best, The Netherlands). Details of the CE-MRA technique have been described previously.13 In brief, time-of flight surveys of the inflow-outflow tract (upper-arm arteries and

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veins) and shunt region were acquired with the patient in a semioblique supine position. A test bolus of 2 mL of gadoteridol (Prohance; Bracco, Milan, Italy), which was injected through a 17-G plastic needle inserted in a vein of the contralateral arm, was used to determine the contrast bolus arrival time at the level of the access. Subsequently, a sagittal T1-weighted fast field-echo sequence of the shunt region was obtained by injection of 20 mL of gadoteridol at a flow rate of 0.6 mL/s (repetition time/echo time/flip angle, 4.1/1.34/20; acquisition voxel size, 1.00 ⫻ 1.00 ⫻ 1.10 mm; interpolated voxel size, 0.84 ⫻ 0.84 ⫻ 0.55 mm; acquisition matrix, 432 ⫻ 346 pixels; 120 slices; overlapping section thickness, 0.55 mm; imaging time, 32 seconds). Finally, a transverse T1-weighted fast field-echo sequence of the inflow and outflow was acquired after injection of 19 mL of gadoteridol at 0.6 mL/s (repetition time/echo time/flip angle, 3.6/1.23/20; acquisition voxel size, 1.17 ⫻ 1.17 ⫻ 1.80 mm; interpolated voxel size, 0.84 ⫻ 0.84 ⫻ 0.90 mm; acquisition matrix, 368 ⫻ 294 pixels; 95 slices; overlapping section thickness, 0.90 mm; imaging time, 32 seconds). Images were reviewed by an MR radiologist, who interpreted the examination at a workstation from the source images and maximum intensity projections. Digital subtraction angiography. To evaluate stenosis within the shunt region and complete venous outflow, an interventional radiologist performed retrograde angiography through a 4-Fr dilator in all patients. The outflow tract was assessed by means of repeated manual injection of 5 to 10 mL of nonionic contrast material (Iomeron 350; Bracco). Flow interruption of the outflow through a cuff or through manual compression was used to visualize the shunt region and adjacent portion of the feeding artery.14 In addition to this standard procedure, DSA of the complete inflow was obtained in all cases in which an arterial stenosis was suspected at CE-MRA. This evaluation was accomplished by advancing a diagnostic catheter over a guidewire into the subclavian artery or aortic arch and performing complete arteriography to show stenoses upstream. Images were recorded by using DSA in multiple planes. Percutaneous transluminal angioplasty (PTA) was performed of stenoses showing a luminal decrease greater than 50% at DSA, and Transonic flow rates were obtained shortly before and within 1 week after PTA.

Definitions The inflow segment included vascular structures from the subclavian artery to the feeding artery 1 cm upstream from the arteriovenous anastomosis (in case of an AVF) or 1 cm upstream from the artery-graft anastomosis (in case of an AVG). The shunt region of an AVF consisted of the arteriovenous anastomosis, including 1 cm of vessel length on both sides of the anastomosis. The AVG region consisted of the arterial and venous anastomosis (including 1 cm of vessel length on both sides of the anastomoses) and loop graft. A vascular stenosis is defined as a decrease in diameter greater than 50% compared with an uninvolved vascular segment located adjacent to the stenosis. The degree of arterial stenosis at CE-MRA and DSA was measured by using an electronic caliper. For cases showing inflow stenosis, coexisting stenoses at the shunt region or venous side also were recorded at DSA to report on the incidence of mixed steno-

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ses. Endovascular intervention was defined as successful if there was less than 30% residual stenosis after angioplasty or stent placement.15 Relief of steal symptoms and improvement of photoplethysmographically derived digital pressures during temporary shunt occlusion were considered objective symptoms of steal.

Statistical Analysis We determined the percentage of arterial stenoses shown by CE-MRA and determined by using DSA. For groups with and without an arterial inflow stenosis, we compared sex distribution, age, number of risk factors for peripheral arterial disease, mean time on hemodialysis therapy, and whether previous shunt interventions had been performed. For continuous variables, Mann-Whitney U test was performed, and for dichotomous variables, a chi-square test. We considered a 2-sided P less than 0.05 to be statistically significant. All analyses were performed using SPSS 11.0.1 (SPSS Inc, Chicago, IL).

RESULTS

Mean duration of hemodialysis therapy among the 101 patients at the time of the CE-MRA examination was 26 months (range, 0 to 147 months). Causes of end-stage renal disease of study patients are listed in Table 1. Diabetes mellitus, hypertension, and dyslipidemia were Table 1. Characteristics of the Patient Population No. of patients Sex Males (%) Type of access AVFs Forearm Elbow Upper arm AVGs Forearm Upper arm Cause of end-stage renal disease Hypertension Diabetic nephropathy Renal artery stenosis Obstructive uropathy Polycystic kidney disease Amyloidosis Glomerulonephritis Hemolytic uremic syndrome Immunoglobulin A nephropathy Chronic pyelonephritis Others Unknown

101 55 66 (65) 24 39 3 35 (35) 31 4 29 (29) 25 (25) 13 (13) 6 (6) 5 (5) 4 (4) 3 (3) 2 (2) 2 (2) 2 (2) 6 (6) 4 (3)

NOTE. Values expressed as number (percent) unless noted otherwise.

present in 32 patients (32%), 73 patients (72%), and 32 patients (32%), respectively. Thirty-six patients (36%) were smokers. Nine patients (9%) had none of these risk factors for peripheral arterial disease, and 1 to 4 risk factors were seen in 38 patients (38%), 33 patients (33%), 16 patients (16%), and 5 patients (5%), respectively. The presence of peripheral arterial disease was documented in 52 patients (51%). Of 101 accesses, 37 (37%) had a history of surgical revision and/or previous endovascular intervention. CE-MRA showed 19 arterial stenoses in 14 of 101 patients (12%). DSA confirmed 18 of these stenoses in 13 patients; the 1 falsepositive reading at CE-MRA probably was caused by a scanning artifact. DSA showed no additional inflow stenoses (Table 2; Figs 1 and 2). Distribution of arterial stenoses was as follows: subclavian artery, 8; axillary artery, 2; brachial artery, 3; and radial artery, 5. Of the 13 patients, 7 patients had arterial stenoses only. One patient had a coexisting stenosis at the venous anastomosis of an AVG. Two AVF patients showed a coexisting stenosis at the arteriovenous anastomosis, and 3 other AVF patients had accompanying stenoses at both the arteriovenous anastomosis and venous outflow. Referral criteria of the 13 patients to undergo CE-MRA had been decreased flow rates (9 patients), steal symptoms (2 patients), and no maturation of an access (2 patients). Regarding the distribution of risk factors in patients with and without arterial stenosis, no differences were found with the exception of patient age; mean age of patients with arterial stenoses was significantly older (72.7 versus 60.5 years; P ⫽ 0.002). The percentage of males was 54.5% in patients without and 61.5% in patients with arterial stenosis (P ⫽ 0.64), the number of risk factors for peripheral arterial disease was 1.7 in patients without and 1.9 in patients with arterial stenosis (P ⫽ 0.28), and mean time on hemodialysis therapy was 26.1 months for patients without and 25.5 months for patients with arterial stenosis (P ⫽ 0.39). The percentage of patients who had undergone a previous shunt intervention also was not statistically significantly different between patients without (36.4%) and with (38.5%) arterial stenosis (P ⫽ 0.883).

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Table 2. Patients With Arterial Access Stenoses: Types of Access, Indications for Radiological Evaluation, Location of Stenoses, and Treatment Outcome

Access

Referral Indication

Location of Arterial Stenosis

Coexisting Stenosis in Shunt Region or Outflow

Endovascular Treatment

Outcome

Radiocephalic AVF Radiocephalic AVF

Steal

Subclavian artery

None

PTA ⫹ stent

Symptom free

Nonmaturation

Radial artery (2 stenoses)

None

PTA

Radiocephalic AVF

Flow decline

Subclavian artery (2 stenoses)

None

PTA ⫹ stent

Radiocephalic AVF

Flow decline

Radial artery

PTA

Radiocephalic AVF

Flow decline

Radial artery

Arteriovenous anastomosis, cephalic vein None

Radiocephalic AVF

Nonmaturation

Subclavian artery

Arteriovenous anastomosis

PTA

Radiocephalic AVF

Flow decline

Brachial artery

Arteriovenous anastomosis

PTA

Brachiocephalic AVF

Flow decline

Subclavian artery

PTA

Brachiocephalic AVF

Steal

Subclavian artery, brachial artery

Arteriovenous anastomosis, cephalic vein None

Brachiocephalic AVF

Flow decline

Axillary artery

PTA

Forearm AVG

Flow decline

Subclavian artery, brachial artery

Arteriovenous anastomosis, cephalic vein Venous anastomosis

Unsuccessful PTA followed by surgical shunt revision Increased flow after PTA (from 526 to 1,185 mL/min) Increased flow after PTA (from 400 to 650 mL/min) Increased flow after PTA (from 406 to 633 mL/min) Successful PTA subclavian artery, followed by surgical shunt revision Increased flow after PTA (from 390 to 650 mL/min) Increased flow after PTA (from 625 to 1,166 mL/min) No clinical success, residual brachial artery stenosis after PTA Increased flow after PTA (from 430 to 760 mL/min) Increased flow after PTA (from 506 to 746 mL/min)

Forearm AVG

Flow decline

Subclavian artery, axillary artery

None

Forearm AVG

Flow decline

Radial artery

None

All patients underwent angioplasty of their stenoses and 4 patients had additional placement of a vascular stent after an unsuccessful subclavian angioplasty procedure (Fig 3). Access flow of the 9 patients with a low-flow access improved from 477 ⫾ 74 to 825 ⫾ 199 mL/min after PTA. One of the patients with steal symptoms became symptom free and had a normal-

PTA

PTA

PTA ⫹ stent subclavian artery, PTA brachial artery ⫹ venous anastomosis PTA ⫹ stent subclavian artery, PTA brachial artery PTA

Increased flow after PTA (from 470 to 860 mL/min) Increased flow after PTA (from 540 to 780 mL/min)

ized photoplethysmography result, whereas the other patient showed no improvement after an unsuccessful endovascular intervention of a brachial artery lesion that showed 50% residual stenosis after angioplasty. Stent placement was not thought to be feasible in this patient because the stenosis was located near the elbow joint, entailing a risk for future stent fracture. Surgical

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Fig 1. Images obtained with 3-dimensional CE (A) MRA and (B) DSA show a brachiocephalic fistula with 3 stenoses. Abbreviations: a, artery; s1, stenosis at the origin of subclavian artery; s2, stenosis at arteriovenous anastomosis; s3, cephalic vein stenosis; v, vein.

revision of 2 nonmaturing shunts was performed after unsuccessful angioplasty. DISCUSSION

Chronic arterial lesions in upper limbs bearing hemodialysis access fistulae and grafts may lead

Fig 2. Images obtained with 3-dimensional CE (A) MRA and (B) DSA show an AVF with 3 stenoses. Abbreviations: a, artery; s1, radial artery stenosis; s2, stenosis just distal to arteriovenous anastomosis; s3, cephalic vein stenosis; v, vein.

to insufficient flow for dialysis treatment, ischemia, and thrombosis. Results of our prospective study show that arterial stenoses are encountered frequently in dysfunctional hemodialysis accesses. At least 1 arterial stenosis in the feeding artery of the shunt was present in 13% of our patients. Most frequently, stenoses were found in the subclavian artery, followed by radial artery lesions as the next to most frequent site of stenosis. It is difficult to compare these findings with those of other studies because the latter were restricted mostly to depiction of the distal feeding artery only. A color duplex ultrasonographic (CDUS) study of upper-extremity AVFs before the initiation of hemodialysis therapy showed inflow stenoses in 5% of patients.16 However, the investigators did not describe whether the complete arterial tree was evaluated at ultrasonography and fistulography did not include assessment of the central arterial inflow. In a retrospective series of 40 patients, Khan and Vesely11 found only 3 brachial artery stenoses and no subclavian artery lesions. They positioned the tip of the angiographic catheter in the subclavian artery distal to the origin of the vertebral artery. Therefore, more centrally located subclavian artery stenoses may not have been depicted. Asif et al12 detected 2 brachial artery lesions and 3 radial artery lesions in a series of 223 patients. A catheter was advanced into the subclavian artery as described by Khan and Vesely11 only if an arterial problem was suspected after subjective assessment of the quality of the access inflow by

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Fig 3. Images obtained with 3-dimensional CE (A) MRA and (B) DSA show the proximal inflow of an access with 2 subclavian artery stenoses (s1, s2). (C) DSA after stent placement. Abbreviation: a, subclavian artery.

blood flow rate evaluation under fluoroscopy and by evaluating pulse augmentation. Although the accuracy of CE-MRA for stenosis depiction in complete access inflow was not validated previously, we believe this imaging modality is a more objective measurement to indicate inflow lesions than the subjective measures described by Asif et al.12 Furthermore, the value of CEMRA for the detection of stenoses in access regions and their venous outflow, as well as its value for the assessment of many other vascular trajectories, such as lower-limb arteries, renal arteries, and carotid arteries, has been well established.13,17-20 To prevent angiography-related cranial artery complications, we only performed complete arterial access DSA of cases in which CE-MRA was suggestive of an arterial problem. Therefore, we are not informed about the possible presence of arterial stenoses in patients with a normal arterial MR examination result. However, DSA detected no additional inflow lesions in patients who had undergone both examinations. In our small group of 4 patients with decreased access flow rates and the finding that arterial stenosis was the only abnormality, the clinical success achieved with arterial PTA proves that these lesions were the only cause of access malfunction. The remaining 5 patients with arterial stenosis in combination with decreased flow also had 1 or several stenoses located at anastomotic sites and/or outflow stenoses. Therefore, we are not informed about the relative contribution of inflow stenoses as a cause of access dysfunction in these cases. Previous reports indicated that approximately one third of patients failed to show an increase in

blood flow after successful angioplasty.7,9,21 This absence of effect may be caused by recoil of the lesion between the angioplasty and first flow rate measurement after PTA, but this finding also may indicate that other hemodynamically important stenoses were not identified and treated. Clinical studies showed that arterial inflow resistance, not venous outflow resistance, was the most significant component of total graft resistance.22,23 Therefore, identification and treatment of arterial stenoses may be important. Greater flows associated with the arteriovenous shunt circuit may unmask inflow lesions that otherwise would have borderline hemodynamic significance. Arterial stenosis probably is common in the aged hemodialysis population, many of whom have generalized arterial disease. We found that the presence of arterial stenosis correlated with patient age; mean age of patients with arterial stenosis was significantly older than that of patients without arterial stenosis. Shoji et al24 suggested that advanced atherosclerosis in hemodialysis patients is caused not by hemodialysis treatment, but by renal failure and/or metabolic abnormalities secondary to renal failure. Conversely, Kushiya et al25 found that patients undergoing hemodialysis have progressive atherosclerosis that is associated with certain hemostatic abnormalities. We currently perform access MRA of all patients who are referred to the interventional radiology department because of access dysfunction for the first time. This baseline examination provides us with a detailed overview of the complete vascular access tree and helps us guide

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interventional procedures. Atherosclerotic lesions gradually arise over years, and in comparison with venous endovascular intervention, inflow stenoses usually have a lower rate of recurrence.10,26 For these reasons, we do not routinely perform MRA of recurring access problems. Too few arterial stenoses will be identified to justify the costs of routine CE-MRA. DSA or CDUS may be used as alternatives to CE-MRA for the evaluation of the arterial tree of a dysfunctional access. A major advantage of DSA is to combine angiography with endovascular intervention in 1 session. Also, costs of DSA are considerably less compared with CE-MRA. A drawback of DSA may be the possible occurrence of catheter-related vertebral artery complications. CDUS is an inexpensive, readily available, and noninvasive examination, although the quality of the images depends on the skill of the operator and CDUS may not detect all stenoses.27,28 Moreover, CDUS traditionally has been used for the evaluation of a shunt region and its outflow segments, but data regarding the value of CDUS for detection of more centrally located arterial stenoses are lacking.29,30 CE-MRA or CDUS may facilitate the interventionalist to perform DSA and angioplasty through providing an appropriate puncture location.30 Whether the costs of an additional CE-MRA or CDUS outweigh the possible benefits of these imaging modalities should, of course, be addressed in a formal cost-effectiveness study. We conclude that it is essential to search for arterial lesions in patients with access thrombosis, insufficient blood flow for dialysis treatment, or symptoms of ischemia in limbs with accesses for hemodialysis. Angiographic evaluation of access inflow should be considered, particularly for patients with persistent access problems. REFERENCES 1. Ballard JL, Blunt TJ, Malone JM: Major complications of angioaccess surgery. Am J Surg 164:229-232, 1992 2. Hill SL, Donato AT: Complications of dialysis access; A six-year study. Am J Surg 162:265-267, 1991 3. Beuter JJG, Lezana AH, Calvo JH, Carriles RS: Early detection and treatment of hemodialysis access dysfunction. Cardiovasc Interv Radiol 23:40-46, 2000 4. Tessitore N, Mansueto G, Bedogna V, et al: A prospective controlled trial on effect of percutaneous transluminal angioplasty on functioning arteriovenous fistulae survival. J Am Soc Nephrol 14:1623-1627, 2003

5. Tessitore N, Lipari G, Poli A, et al: Can blood flow surveillance and pre-emptive repair of subclinical stenosis prolong the useful life of arteriovenous fistulae? A randomized controlled study. Nephrol Dial Transplant 19:23252333, 2004 6. Kanterman RY, Vesely TM, Pilgram TK, Guy BW, Windus DW, Picus D: Dialysis access grafts: Anatomic location of venous stenosis and results of angioplasty. Radiology 195:135-139, 1995 7. Van der Linden J, Smits JH, Assink JH, et al: Shortand long-term functional effects of percutaneous transluminal angioplasty in hemodialysis vascular access. J Am Soc Nephrol 13:715-720, 2002 8. Beathard GA: Angioplasty for arteriovenous grafts and fistulae. Semin Nephrol 22:202-210, 2002 9. Schwab SJ, Oliver MJ, Suhocki P, McCann R: Hemodialysis arteriovenous access: Detection of stenosis and response to treatment by vascular access blood flow. Kidney Int 59:358-362, 2001 10. Guerra A, Raynaud A, Beyssen B, Pagny J, Sapoval M, Angel C: Arterial percutaneous angioplasty in upper limbs with vascular access devices for haemodialysis. Nephrol Dial Transplant 17:843-851, 2002 11. Khan FA, Vesely TM: Arterial problems associated with dysfunctional hemodialysis grafts: Evaluation of patients at high risk for arterial disease. J Vasc Interv Radiol 13:1109-1114, 2002 12. Asif A, Gadalean FN, Merrill D, et al: Inflow stenosis in arteriovenous fistulas and grafts: A multicenter, prospective study. Kidney Int 67:1986-1992, 2005 13. Froger CL, Duijm LEM, Liem YS, et al: Stenosis detection with MR angiography and digital subtraction angiography in dysfunctional hemodialysis access fistulas and grafts. Radiology 234:284-291, 2005 14. Staple TW: Retrograde venography of subcutaneous arteriovenous fistulas created surgically for hemodialysis. Radiology 106:223-224, 1973 15. National Kidney Foundation: K/DOQI Clinical Practice Guidelines for Vascular Access: Update 2000. Am J Kidney Dis 37:S137-S181, 2001 (suppl 1) 16. Grogan J, Castilla M, Lozanski L, Griffin A, Loth F, Bassiouny H: Frequency of critical stenosis in primary arteriovenous fistulae before hemodialysis access: Should duplex ultrasound surveillance be the standard of care? J Vasc Surg 41:1000-1006, 2005 17. Smits JHM, Bos C, Elgersma OEH, et al: Hemodialysis access imaging: Comparison of flow-interrupted contrastenhanced MR angiography and digital subtraction angiography. Radiology 225:829-834, 2002 18. Ho KY, Leiner T, de Haan MW, Kessels AG, Kitslaar PJ, van Engelshoven JM: Peripheral vascular tree stenoses: Evaluation with moving-bed infusion-tracking MR angiography. Radiology 206:683-692, 1998 19. Ouwendijk R, de Vries M, Pattynama PMT, et al: Imaging peripheral arterial disease: A randomized controlled trial comparing contrast-enhanced MR angiography and multi-detector row CT angiography. Radiology 236:10941103, 2005 20. Anzalone N, Scomazzoni F, Castellano R, et al: Carotid artery stenosis: Intraindividual correlations of 3D time-of flight MR angiography, contrast-enhanced MR an-

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giography, conventional DSA, and rotational angiography for detection and grading. Radiology 236:204-213, 2005 21. Ahya SN, Windus DW, Vesely TM: Flow in hemodialysis grafts after angioplasty: Do radiologic criteria predict success? Kidney Int 59:1974-1978, 2001 22. Bosman PJ, Boereboom FT, Smits HF, Eikelboom BC, Koomans HA, Blankestijn PJ: Pressure or flow recordings for the surveillance of hemodialysis grafts. Kidney Int 52:1084-1088, 1997 23. van Stone JC, Jones M, van Stone J: Detection of hemodialysis access outlet stenosis by measuring outlet resistance. Am J Kidney Dis 23:562-568, 1994 24. Shoji T, Emoto M, Tabata T, et al: Advanced atherosclerosis in predialysis patients with chronic renal failure. Kidney Int 61:2187-2192, 2002 25. Kushiya F, Wada H, Sakakura M, et al: Atherosclerotic and hemostatic abnormalities in patients undergoing hemodialysis. Clin Appl Thromb Hemost 9:53-60, 2003

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26. Sprouse LR II, Lesar CJ, Meier GH III, et al: Percutaneous treatment of symptomatic central venous stenosis. J Vasc Surg 39:578-582, 2004 27. Bay WH, Henry ML, Lazarus JM, Lew NL, Ling J, Lowrie EG: Predicting hemodialysis access failure with color flow Doppler ultrasound. Am J Nephrol 18:296-304, 1998 28. Wiese P, Nonnast-Daniel B: Colour Doppler ultrasound in dialysis access. Nephrol Dial Transplant 19:19561963, 2004 29. Schwarz C, Mitterbauer C, Boczula M, et al: Flow monitoring: Performance characteristics of ultrasound dilution versus color Doppler ultrasound compared with fistulography. Am J Kidney Dis 42:539-545, 2003 30. Doelman C, Duijm LEM, Liem YS, et al: Stenosis detection in failing hemodialysis access fistulas and grafts: Comparison of color Doppler ultrasonography, contrastenhanced magnetic resonance angiography and digital subtraction angiography. J Vasc Surg 42:739-746, 2005