Creation of a Transrenal Arteriovenous Dialysis Shunt: Feasibility Study in a Swine Model

Creation of a Transrenal Arteriovenous Dialysis Shunt: Feasibility Study in a Swine Model Michael J. Wallace, MD, Michael Middlebrook, MD, and Kenneth C. Wright, PhD

PURPOSE: To investigate the feasibility of percutaneous renal artery and vein access for the creation of a transrenal arteriovenous hemodialysis graft. MATERIALS AND METHODS: Renal-artery-to-ipsilateral-renal-vein conduits were constructed with use of entirely percutaneous techniques in seven swine. Renal artery and vein access was performed in six animals with use of a retrograde (inside-out) technique and in one animal with use of an antegrade (outside-in) technique. Modified 8-F sheaths were used in the first three animals and Wallgrafts were used in the final four animals to form the arterial and venous limbs of each shunt. The arterial and venous limbs were joined together by a subcutaneous segment of 6-mm reinforced polytetrafluoroethylene (PTFE) in five animals and by external conduits in two animals. Wallgrafts were deployed from the renal artery and vein into the segments of PTFE. The free ends of each conduit were tunneled and joined together to close the arteriovenous circuit. Post-shunt angiography was used in all animals to document successful shunt creation and demonstrate rapid arteriovenous shunting as a determinant of technical feasibility. Two of the seven animals received additional anticoagulation therapy and/or antiplatelet therapy to prevent shunt thrombosis during the follow-up period. The three initial animals were killed within 2 hours of shunt creation, and two of the remaining four animals returned for angiographic follow-up, one on day 2 and one on day 9. All animals underwent a complete necropsy to assess for potential complications including hemorrhage and vascular or bowel injury. RESULTS: Retrograde renal arterial and venous access was successful in all six animals in which it was attempted. Five of six arterial accesses and four of six venous accesses traversed the peritoneum with two arterial accesses and one venous access penetrating a loop of large bowel. Antegrade access was performed and successfully accomplished in the final animal. Brisk arteriovenous shunting was demonstrated on completion angiography in all animals. Graft occlusion was present in the two animals that returned for follow-up and two animals died before follow-up as a result of graft leakage and subsequent hemorrhage. Minimal perinephric and intrarenal hemorrhage was demonstrated at necropsy after shunt insertion in the remaining five animals. Renal infarction was present in all kidneys used for transrenal access. CONCLUSION: The transrenal approach for the creation of a percutaneous arteriovenous shunt is feasible after renal artery and vein access by either the retrograde or antegrade technique. Additional technical refinements of the procedure and the devices used will be necessary before follow-up studies are conducted. Index terms:

Dialysis, shunts

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Shunts, arteriovenous

J Vasc Interv Radiol 2001; 12:1325–1332 Abbreviations:

IVC ⫽ inferior vena cava, PTFE ⫽ polytetrafluoroethylene

DURING the past decade, percutaneous management of dysfunctional or

From the Department of Diagnostic Radiology (M.J.W., K.C.W.), The University of Texas M.D. Anderson Cancer Center and Department of Radiology (M.M.), The University of Texas Health Science Center at Houston (M.M.), Houston, Texas. Received May 4, 2001; revision requested June 19; revision received and accepted July 23. Supported in part by a grant from the John S. Dunn Research Foundation and by grant NIHNCI CA-16672 from the National Cancer Institute. Address correspondence to M.J.W., University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Box 325, Houston, TX 77030-4009; E-mail: mwallace@ di.mdacc.tmc.edu © SCVIR, 2001

thrombosed hemodialysis access has become the mainstay of therapy in attempts to maximize shunt survival. Despite aggressive surveillance and intervention, the survival rates remain unsatisfactory, even in those patients who present before graft thrombosis (1). These percutaneous maneuvers have included chemical and mechanical thrombolysis or thrombectomy, balloon angioplasty, and stent placement. These techniques are simply temporary solutions to extend the patency of an inherently unfavorable circumstance. The weakness of synthetic arm grafts revolves around the ve-

nous anastomosis, where nonphysiologic hemodynamics at the junction between the synthetic graft and native vessels result in the formation of intimal hyperplasia, graft stenosis, and inevitable failure (2). Patient survival is therefore directly linked to the finite number of arteriovenous grafts and fistulas that can be placed in four extremities. A new approach with an alternative access site would at least provide additional sites for graft placement. An additional access with improved durability would be a true advancement in hemodialysis management.

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Transrenal Arteriovenous Shunt Experimental Details Animal Wt No. (kg) Sex

Preprocedural Anticoagulation

Preprocedural Antiplatelet Therapy

1

46.8 F

None

None

2

44.4 F

None

None

3

52.8 F

None

4

37.5 F

5

Procedural Heparin

Postprocedural Antiplatelet Therapy

Postprocedural Anticoagulation

Renal Access

100 U/kg; 50 U every 30 min 100 U/kg; 50 U every 30 min

None

None

Retrograde

None

None

Retrograde

None

100 U/kg; 50 U every 30 min

None

None

Retrograde

None

None

Initial 100 U/kg; 50 every None 30 min

None

Retrograde

37.7 M

None

None

Initial 100 U/kg; 100 every 30 min

None

Aspirin 1 mg/kg (2 d)

Retrograde

6

38.7 F

None

Aspirin 1 mg/kg (24 h earlier)

100 U/kg; 50 U every 30 min

None

Aspirin 1 mg/kg

Retrograde

7

57.6 F

Warfarin 0.08 mg/kg/d

Persantine* 1 mg Antegrade three times daily

100 U/kg; 50 U every Warfarin 0.08 mg/kg/d Persantine 1 mg 30 min started 1 wk earlier three times daily (1 wk earlier)

Note.—SC ⫽ subcutaneous, A & V ⫽ arterial and venous, RP ⫽ retroperitoneal, IP ⫽ intraperitoneal. * Boehringer Ingelheim, Ridgefield, CT.

Covered stents have emerged and are being investigated for use in a variety of vascular and nonvascular endoluminal applications. It is believed that the covering will provide a barrier and exclude aneurysms and arterial injuries and improve patency after vascular occlusive interventions or endourologic and endobiliary stent placement. As this technology advances, endoluminal applications may eventually give rise to exoluminal techniques to create percutaneous extra-anatomic bypasses. The purpose of this study is to determine the feasibility of percutaneous renal artery and vein access for the creation of a percutaneous extra-anatomic transrenal arteriovenous graft as a potential alternative shunt for hemodialysis.

MATERIALS AND METHODS All experimentation involving animals was approved by the Institutional Animal Care and Use Committee of our institution. Animals were maintained in facilities approved by the Association for Assessment and Accreditation of Laboratory Animal Care International and in accordance with current U.S. De-

partment of Agriculture, Department of Health and Human Services, and National Institutes of Health regulations and standards. Seven adult domestic swine (37.5– 57.6 kg) were used to investigate the feasibility of percutaneous renal access for transrenal arteriovenous shunt creation. Each animal was sedated with an intramuscular injection of a solution containing ketamine hydrochloride (15 mg/kg), acepromazine (0.15 mg/kg), and atropine sulfate (0.4 mg/ kg). Anesthesia was induced with isoflurane (5%) and maintained with isoflurane (1.5%–2%) and oxygen (0.8 L/min) after tracheal intubation. The femoral artery and vein were isolated and cannulated by a cutdown, and long 9-F vascular sheaths were inserted into the aorta and inferior vena cava (IVC) just below the right renal artery and vein. All animals received heparin infusion (100 U/kg) after vascular access was established and were administered heparin boluses of 50 U/kg every 30 minutes. Three of the seven animals received additional perioperative anticoagulation or antiplatelet therapy (Table).

In the first six animals, percutaneous access to the right renal artery and vein was accomplished by a retrograde (inside-out) technique. After selective right renal digital subtraction angiography and venography, an 8-F MPA Lumax guide catheter (Cook, Bloomington, IN) was advanced into a second- or thirdorder renal vessel. The back ends of modified (sharpened) 0.038-inch Glidewires (Boston Scientific/Medi-tech, Watertown, MA) were advanced from the renal vessels to the flank and subcutaneous tissues (Fig 1). Separate 2-cm incisions were made in the overlying skin to retrieve the Glidewires, resulting in through-and-through access. In the seventh animal, an antegrade (outside-in) technique was used to access the renal vasculature. Two 9-F angled flexor sheaths (Cook) were inserted into a second- or third-order right renal artery and vein. Under fluoroscopic guidance, 18-gauge needles were advanced from the flank into the radiopaque tip of each sheath (Fig 2). An exchange length (260 cm) Amplatz super-stiff guide wire (Boston Scientific/Medi-tech) was inserted for through-and-through access. Modified sheaths (Fig 3) were used

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Conduit

Follow-up

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Traversed Bowel

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Necropsy Results

8-F Sheath

External

Immediate sacrifice

A&V

No

No significant renal hemorrhage

Modified Flexible 8-F Sheath

External PTFE

Immediate sacrifice

A&V

No

Modified Flexible 8-F Sheath

SC PTFE 15 cm

Killed at 3 h

A&V

V

30-F track master/Wallgraft

SC PTFE 10 cm

Reexamined at 2 d; graft occluded (killed)

None

No

30-F track master/Wallgraft

SC PTFE 10 cm

Died at 4 h

A&V

A

30-F track master/Wallgraft

SC PTFE 10 cm

Reexamined at 9 d; graft occluded (killed)

A

A

30-F track master/Wallgraft

SC PTFE 3 cm

Died within 60 h

None

No

Infarction without significant parenchymal or subcapsular hemorrhage Infarction without significant parenchymal or subcapsular hemorrhage Infarction without significant parenchymal or subcapsular hemorrhage Retroperitoneal/intraperitoneal hemorrhage; leaking through Wallgraft Infarction without significant parenchymal or subcapsular hemorrhage; firm thrombus in graft Large amount of RP with/minimal IP hemorrhage; PTFE & Wallgraft separation possibly from leaking through graft

as the axial components in the first three shunts. The axial component was defined as that segment of the shunt that extends from the renal artery and vein to the flank. The arterial and venous limbs were connected by nontunneled conduits in the first two animals (Fig 4) and tunneled in the third animal. The valve and side-arm portion of the sheaths provided hemostasis during the procedure but were removed just before connection with the polytetrafluoroethylene (PTFE) conduit. The conduits were joined to the sheaths by modified Luer locking hubs that were preattached to the PTFE and wedge fit to the cut sheath. The first two animals provided the initial experience with transrenal vascular access. Shunts in the last four animals used Wallgrafts (Boston Scientific/Medi-tech) to create the arterial and venous limbs (Fig 5) as a means to increase the diameter of the axial components and improve fixation within the main renal artery and vein to prevent movement and erosion that may occur with catheter-based devices. To overcome the inadequately short lengths of available Wallgrafts (8 mm in diameter, 70 mm long), reinforced PTFE was inserted down to the capsule of the

kidney through a 30-F sheath. An Amplatz TractMaster system (Boston Scientific/Medi-tech) was used to dilate the tract and insert the sheaths down to the renal margin (Fig 6). A 20-cm segment of PTFE was back-loaded onto the shaft of the Wallgraft delivery system and both were inserted through the 30-F sheath. The PTFE was advanced to the renal cortex and the Wallgraft was inserted and deployed from the renal vascular origins into the PTFE. In the last animal, a 2.5-cm-long, 26-F segment of an Amplatz dilator (Cook) was bonded to a portion of the PTFE (Fig 5) with commercially available cyanoacrylate to stiffen the retroperitoneal segment of the graft and simplify insertion. Angioplasty balloons (5 mm and 6 mm in diameter by 2 cm long) were then positioned within the renal artery and vein, respectively, and inflated in the mid portion of both Wallgrafts for hemostasis until the circuits were complete. The two limbs of the graft were then tunneled and joined at the apex with a 2-cm segment of thin-walled aluminum tubing. Each end of the PTFE was frictionfit over the metal tubing and butted together. The fit was tight enough that additional adhesives or sutures did not

appear necessary. The arterial limb was dilated to 5 mm, and the venous limb was dilated to 6 mm. Completion angiograms were obtained in all animals (Fig 5) to document successful shunt creation and demonstrate rapid arteriovenous shunting as a determinant of overall technical feasibility. The length of tunneled PTFE graft ranged from 3 cm to 15 cm. The first three animals were killed with an intravenous overdose of Beuthanasia-D (1 mL per 10 lb; ScheringPlough, Kenilworth, NJ) within 2 hours after shunt creation. Shunts in the last four animals were created with sterile technique and animals were recovered from anesthesia and scheduled for follow-up on day 2 (n ⫽ 1), day 7 (n ⫽ 2), or day 9 (n ⫽ 1) based on physician and lab availability. The purpose of follow-up was to gain initial information regarding the need for adjunctive anticoagulation or antiplatelet therapy should future studies be warranted. All animals underwent a complete necropsy whereby the involved kidney, appropriate juxtarenal aorta and IVC, perinephric tissues, and overlying skin and subcutaneous tissues were removed. The specimens were grossly examined

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Figures 1, 2. (1) A spot frontal view during retrograde transrenal access demonstrates the sharpened Glidewire with the tip (arrow) traversing the retroperitoneum approaching the subcutaneous tissues. Note that a second guide wire has already been advanced and retrieved through the skin of the flank. (2) A lateral image during fluoroscopy after insertion of two 18-gauge needles from the flank into the renal arterial and venous sheaths with subsequent insertion of a guide wire for through-and-through access.

for the presence of intrarenal or perinephric hemorrhage/hematoma, vascular injury to the central renal vessels, aorta, IVC, or adjacent viscera.

RESULTS Percutaneous renal artery and vein access with subsequent arteriovenous shunt creation was successful in all seven animals. Both retrograde (n ⫽ 6) and antegrade (n ⫽ 1) approaches were technically feasible for transrenal access. The mean procedure duration was 2.5 hours and ranged from 2 to 4 hours, depending on the complexity of the devices and the delivery systems used. Angiographic evidence of rapid shunting was noted in all animals at the completion of the procedure. Infarction of the right kidney was noted in all animals at necropsy. The path of transrenal access was within 1 cm of the mid-coronal plane when the retrograde technique was used. In these six animals, nine of the 12 graft limbs traversed the peritoneum, and four limbs penetrated the large bowel (Fig 3). Five of the seven animals did not have retroperitoneal, peritoneal or nephric/perinehpric hemorrhage (Fig 3). Shunt occlusion was identified in two

of the four animals (No. 4 and No. 6) that returned for follow up. Animals 5 and 7 died 4 hours and 60 hours, respectively, after shunt creation, presumably related to the administration of additional anticoagulation and/or antiplatelet therapy beyond the standard procedural heparinization. Both demonstrated Wallgraft leakage with hemorrhage as the probable cause of death. Peritoneal and retroperitoneal hemorrhage was present in animal 5 (retrograde approach) where renal access passed through the peritoneal cavity. Retroperitoneal hemorrhage alone was identified in animal 7 (antegrade approach), and graft separation at the Wallgraft/ PTFE junction was identified. Graft separation was not found in the other three animals in which Wallgrafts were used.

DISCUSSION Hemofiltration via upper extremity arteriovenous synthetic grafts is the predominant method by which patients in the United States receive dialysis. There have been no changes in the materials, techniques, or access sites in the last 20 years that have dramatically improved the primary surgical patency of these grafts. In the past 10 years, a shift in strategy to prolong

arteriovenous graft survival has involved a more aggressive surveillance program whereby stenoses are treated before graft thrombosis ensues. The primary 12-month patency rate following angioplasty alone in the absence of thrombosis is between 23% and 44%, and the 12-month secondary patency rate is 81%– 82% (1). In the presence of thrombosis, graft survival is dramatically reduced, with 6-month primary patency rates of 18%–39% (1). To date, the use of vascular stents has not resulted in any significant improvement in graft patency (3–5). Covered stents are now being investigated as an additional tool to improve shunt survival (6,7). It is apparent that mechanical maneuvers at the venous anastomosis are insufficient to overcome stenoses secondary to intimal hyperplasia as the dominant cause of graft failure (2). More recently, approaches to prolong arteriovenous graft survival have focused on the inhibition of intimal fibromuscular hyperplasia (8 –11). As the number of patients requiring hemodialysis increases, the need for alternative, longer-lasting access becomes more critical. The transrenal approach

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Figures 3, 4. (3) Necropsy image within 30 minutes after shunt creation demonstrates two modified sheaths exiting the renal parenchyma near the midcoronal plane. Perinephric hemorrhage is absent, but both limbs of the shunt traverse the peritoneum and one limb penetrates bowel (arrow). (4) Photograph of reinforced PTFE external conduit that joins inflow and outflow limbs (modified sheaths) to complete the shunt circuit.

was devised to minimize or eliminate the high-velocity hemodynamic stresses that produce intimal hyperplasia in small-caliber veins of upper extremity PTFE accesses. Two critical elements were considered in the decision to use the kidney as a novel hemodialysis access site. The first is the limited clinical consequence of the loss of one nonfunctioning kidney as a result of creating an arteriovenous shunt. The complications of renal embolization and infarction are well documented, with the most common complication being postembolization syndrome consisting of fever, nausea, vomiting, and pain (12). Other potential complications include hypertension and abscess formation (12,13). The second is that the venous limb of the shunt can be extended directly to the IVC. It is believed that the IVC, because of its size, can tolerate the hemodynamic stresses that result from graft insertion. Central venous stenoses and occlusions that have been identified in patients receiving upper extremity hemodialysis are most commonly the result of earlier central venous access (14 –16) rather than a sequela of arteriovenous graft in-

sertion and subsequent hemodynamic stresses. A major potential challenge that may arise in the clinical application of this alternative approach to dialysis access is the presence of atrophic kidneys and superimposed atherosclerotic disease, which is common in the population undergoing chronic dialysis treatment. In the absence of renal arterial occlusion, this approach may still be viable. The renal artery is simply a conduit; therefore, the use of adjunctive angioplasty could provide enough diameter restoration to insert the delivery system of the covered stent. The covered stent can be deployed slightly into the aorta and dilated to the desired diameter. The covering on the stent should prevent any sequela of arterial injury from overdilation. With advances in endovascular techniques and the development of covered stents (endoprostheses), new percutaneous endoluminal approaches in the treatment of vascular aneurysms (17–19) and occlusions (20,21) have begun. Several stent-graft designs are currently available and have been used successfully to ex-

clude abdominal aortic aneurysms by creating endoluminal bypasses (17–19). The transjugular intrahepatic portosystemic shunt is the first clinically used example of a completely percutaneous extra-anatomic bypass between the portal vein and hepatic vein through the liver parenchyma (22–24). During the early 1990s, when the transjugular intrahepatic portosystemic shunt was increasing in popularity, covered stents had not evolved enough for clinical use. The transhepatic nature of the procedure allowed the liver parenchyma to act as a covering to prevent hemorrhage. Current investigation in the use of covered stents for transjugular intrahepatic portosystemic shunt to improve shunt patency is in progress (25–27). In an experimental model, Trerotola et al (28) reported the creation of a percutaneous arteriovenous hemodialysis graft from the common femoral artery to the common femoral vein with use of silicone-covered Wallstents. Technical success was achieved, but issues relating to graft leakage and dislodgment were noted. A first critical step for the transrenal approach is the ability to access the

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Figure 5. Unsubtracted (a) and subtracted (b) angiography, in the lateral projection, after transrenal shunt creation in animal 7 with use of Wallgrafts and reinforced PTFE demonstrates rapid flow from the renal artery origin (arrow) to the vena cava (open arrow). A segment of 26-F dilator (asterisk) was bonded to a portion of the PTFE to stiffen the retroperitoneal portion of the conduit and simplify its insertion. Contrast material is also present within the contralateral ureter (arrowhead).

Figure 6. A lateral fluoroscopic spot image demonstrating the use of the Amplatz TractMaster system to dilate the retroperitoneum to allow insertion of reinforced PTFE to the renal margin.

renal vessels within the renal parenchyma. This is considered important to allow ease of sheath insertion by providing a stable parenchymal/vessel interface and by reducing procedure-related hemorrhage. The secondand third-order renal arteries and

veins serve as good entry sites. There is adequate parenchymal support, and the distance to the aorta and IVC is sufficient for slight movement that occurs with respiration. This addresses the potential for either the sheath or the covered stent to migrate into the

tract before device incorporation. The retrograde approach was initially used to accomplish renal access because it was believed to be easier to reliably choose an exit site from within the vasculature rather than an entry site by a percutaneous technique. An additional advantage considered was the lack of over-the-wire exchanges at the vessel entry site to reduce the risk of procedural hemorrhage. This approach has been described as a technique for performing retrograde nephrostomy (29,30). This technique is feasible and rather easy to perform, but the ability to control the path of the guide wire is difficult when it leaves the vessel. The path favors a lateral direction rather than a posterolateral direction. This is important in the animal model, in which the perinephric fat is sparse and the bowel interposes itself between the kidney and the flank (Fig 7). In the experimental animal, the sharpened guide wire tends to exit anterior to the midcoronal plane of the kidney. In the absence of adequate perinephric fat, there is a higher potential risk of traversing the peritoneal cavity and penetrating the colon than in a human. The distance to the skin is consider-

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plify the technique and examine alternative stent graft platforms and coverings are needed before extended experimental follow-up studies.

Figure 7. Noncontrast CT scan of the abdomen of a swine demonstrates the lack of perinephric fat with the interposition of bowel between the kidney and flank.

ably longer with retrograde approach than with the antegrade approach. The effective renal artery and vein entry sites were similar, but the path was easier to control, shorter, and confined to the retroperitoneum. The sheaths inserted from the femoral access provided adequate targets for percutaneous needle insertion. Alternatively, a small snare could be used as the fluoroscopic landmark and mechanism for acquiring through-and-through guide wire access. This latter maneuver is crucial for maximum control during subsequent graft deployment and temporary graft balloon occlusion. Both approaches may show clinical viability in the future. Excluding the two animals that received additional anticoagulation and/or antiplatelet therapy, necropsy did not demonstrate significant procedure-related hemorrhage around or within the kidney. The second major step is the creation of arterial and venous limbs. Modified sheaths were easy to use but would not be a viable long-term solution. The internal diameter of these sheaths would be too small, and securing their tips into place would be difficult. This may result in dislodgment, vascular erosion, or possible perforation from to-and-fro movement at the tip caused by respiration. Wallgrafts were not used in the first three animals because of the lack of adequate lengths of stent-grafts in excess of 10 cm. After

the success of transrenal access in the first group of animals, an alternate system was devised to incorporate available Wallgrafts. The issue of length was overcome with the use of a complex delivery system that allowed the insertion of the PTFE graft material down to the kidney. Although we were successful in performing this task, the required steps added at least 1 hour to the overall procedure time. An alternative covered stent that is longer and has a less porous covering will be used in the next phase of this study. Leakage through the Dacron polyethyleneteraphthalate covering was the presumed cause of premature death secondary to hemorrhage in the two animals in which coagulation and/or platelet function was manipulated. The Wallgraft covering is a woven polyester yarn with medium porosity. Percutaneous extra-anatomic bypasses or shunts may require a less porous material like PTFE to prevent leakage, especially in the presence of aggressive anticoagulation or antiplatelet therapy. In summary, we have demonstrated the feasibility of percutaneous renal artery and vein access as a possible alternative site for the creation of a percutaneous arteriovenous hemodialysis graft. Both antegrade and retrograde approaches are viable techniques for accomplishing this unusual type of access. Further studies to sim-

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