Hemodialysis fistulas are surgically created communications between the native artery and vein in an extremity. Direct communications are called native arteriovenous fistulas (AVFs). Polytetrafluoroethylene (PTFE) and other materials (Dacron, polyurethane, bovine vessels, saphenous veins) are used or have been used as a communication medium between the artery and the vein and are termed prosthetic hemodialysis access arteriovenous grafts (AVGs). The access that is created is routinely used for hemodialysis 2-5 times per week.
Many patients who are not candidates for renal transplantation or those for whom a compatible donor cannot be secured are dependent on hemodialysis for their lifetime. This situation results in the long-term need for and use of dialysis access. The preservation of patent, well-functioning dialysis fistulas is one of the most difficult clinical problems in the long-term treatment of patients undergoing dialysis. As many as 25% of hospital admissions in the dialysis population have been attributed to vascular access problems, including fistula malfunction and thrombosis.
History of the Management of Dialysis Access
Historically, native fistula or graft malfunction and thrombosis were treated by using surgical thrombectomy and revision, resulting in the eventual exhaustion of the veins and the need to create a new access. Initially applied in the 1980s, percutaneous techniques such as balloon angioplasty (percutaneous transluminal angioplasty [PTA]), thrombolysis, and mechanical thrombectomy allowed the treatment of stenosis and fistula thrombosis without surgery.
In the past 2 decades, interventional radiologists have increasingly been involved in angiographic evaluation and treatment of malfunctioning and occluded hemodialysis access. The multidisciplinary management of dialysis access coordinated among interventional radiologists, vascular surgeons, and nephrologists has proven extremely effective in prolonging the patency of the vascular access and decreasing the morbidity and mortality of patients with chronic renal failure.
Examples of a vessel with long-segment stenosis before and after treatment are provided below.
Less than 15% of dialysis fistulas remain patent and can function without problems during the entire period of a patient’s dependence on hemodialysis. The mean problem-free patency period after creation of native fistulas is approximately 3 years, whereas prosthetic polytetrafluoroethylene (PTFE) grafts last 1-2 years before indications of failure or thrombosis are noted. After multiple interventions to treat underlying stenosis and thrombosis, the long-term secondary patency rates for native fistulas are reportedly 7 years for fistulas in the forearm and 3-5 years for fistulas in the upper arm; prosthetic grafts remain patent for up to 2 years.
Causes of Dialysis Fistula Failures
To the authors’ knowledge, all observations and publications reported to date indicate that for prosthetic grafts, fistula failure and eventual occlusion occur most commonly as a result of the progressive narrowing of the venous anastomosis; for native fistulas, failure occurs most commonly as a result of the narrowing of the outflow vein. In some reports, venous anastomosis is identified in more than 90% of grafts. The primary underlying pathophysiologic mechanism responsible for causing the failure is intimal hyperplasia at the anastomotic site. Additional causes include surgical and iatrogenic trauma, such as repeated venipunctures. Stenoses along the venous outflow and in intragraft locations (for prosthetic PTFE grafts) are also common and require appropriate treatment.
When to consult with an Interventional Radiologist
The following are indications for consultation with an interventional radiologist:
→ Abnormal findings on clinical examination, such as weak thrill or pulsatility
→ Direct palpation of stenosis
→ Insufficient inflow, such as stenosis in the supplying native artery or proximally in the subclavian or brachiocephalic artery
→ Vacuum phenomenon
→ Identification of high venous pressures in accordance with the protocol appropriate for the specific type of hemodialysis machine
→ Suboptimal blood flow (according to the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative 1997 guidelines: 700-800 mL/min for prosthetic grafts and 500 mL/min for native fistulas) or recirculation while the patient receives hemodialysis.
→ Demonstration of stenoses in a previous Doppler ultrasonographic examination
→ Ipsilateral arm edema and/or collateral venous pathways suggestive of a central venous stenosis
The presence of an infection is the only absolute contraindication to angiography and percutaneous treatment of a dysfunctional or thrombosed dialysis access.