Interventional Radiology Imaging

What Imaging Is Best for a Dialysis Fistula with Decreasing Flow Rates?

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What Imaging Is Best for a Dialysis Fistula with Decreasing Flow Rates?

A dialysis technician flags a patient’s chart: for the third consecutive session, the arteriovenous fistula’s (AVF) blood flow rate has dropped, now well below the 500 mL/min threshold. The patient has no new arm swelling or pain, but the dialysis adequacy, measured by urea reduction ratio (URR), is trending down. This subtle but persistent hemodynamic change signals a brewing problem that, if ignored, could lead to access failure. You need to identify the cause and plan a potential intervention before the access is lost. This clinical workflow article addresses the initial imaging choice for suspected hemodialysis access dysfunction based on abnormal clinical or hemodynamic indicators. For this scenario, the American College of Radiology (ACR) designates Fluoroscopy fistulography hemodialysis access area of interest as Usually Appropriate.

Who Fits This Clinical Scenario?

This guidance applies to patients with a mature, functioning upper or lower extremity hemodialysis access—either an arteriovenous fistula (AVF) or an arteriovenous graft (AVG)—who now present with signs of dysfunction. The key indicators are not acute or catastrophic but rather a gradual decline in performance. These signs include:

  • A documented reduction in dialysis vascular access blood flow rate.
  • Decreased dialysis adequacy (e.g., falling Kt/V or URR).
  • Increased venous pressures during dialysis.
  • Difficulty with cannulation or prolonged bleeding post-cannulation.

This workflow is distinct from other access-related problems. It does not apply to:

  • Acute Thrombosis: A patient with a sudden absence of a palpable thrill or audible bruit. This is an emergent condition suggesting complete occlusion and follows a different diagnostic and therapeutic pathway.
  • Failure to Mature: A newly created AVF that has not become adequate for cannulation within 2-3 months of creation. This workup focuses on identifying anatomical reasons for maturation failure, such as competing accessory veins.
  • Suspected Central Venous Stenosis: A patient presenting primarily with ipsilateral arm, breast, or facial swelling. While central stenosis can cause access dysfunction, this presentation points specifically to a more central problem requiring a tailored imaging approach.

What Diagnoses Are You Working Up in This Scenario?

When a dialysis access shows declining function, the underlying cause is almost always a structural issue that impedes blood flow. The imaging workup is designed to identify and characterize these problems to guide intervention.

The most common cause is a flow-limiting stenosis. These stenoses typically develop due to neointimal hyperplasia, a response to the turbulent, high-flow environment. They can occur at several key locations: the arterial anastomosis (where the artery is connected to the fistula/graft), within the body of the fistula or graft itself, or, most frequently, at the venous anastomosis or in the primary draining vein.

A non-occlusive thrombus is another important consideration. Small clots can form in areas of low flow or stenosis, further compromising the lumen and reducing flow rates. While not a complete blockage, this can be a precursor to acute thrombosis if the underlying stenosis is not addressed.

Less commonly, the issue may be an accessory draining vein. In some fistulas, a side branch vein can “steal” a significant portion of the arterial inflow, preventing the primary access circuit from achieving adequate flow for dialysis. This is more often a cause of maturation failure but can also contribute to later dysfunction.

Finally, central venous stenosis in the subclavian vein, brachiocephalic vein, or superior vena cava can cause increased back-pressure on the entire circuit, leading to elevated venous pressures during dialysis and reduced flow. While often accompanied by arm swelling, it can sometimes present more subtly with only hemodynamic changes.

Why Is Fluoroscopic Fistulography the Recommended Study for This Presentation?

The ACR rates both Fluoroscopy fistulography hemodialysis access area of interest and US duplex Doppler hemodialysis access area of interest as Usually Appropriate. However, for guiding interventional therapy, fistulography is the definitive study.

A fistulogram, also known as a dialysis access angiogram, is the gold standard for evaluating access dysfunction. It involves direct cannulation of the access and injection of iodinated contrast under fluoroscopy. This provides a dynamic, real-time map of the entire circuit, from the arterial inflow, through the fistula or graft, and into the central veins. Its primary advantage is that it is both diagnostic and therapeutic. If a significant stenosis is identified, angioplasty (ballooning the vessel open) or stenting can often be performed during the same procedure, restoring function immediately. This “one-stop-shop” approach is highly efficient and clinically effective.

Duplex ultrasound is an excellent non-invasive alternative. It uses sound waves to visualize the access and Doppler to measure blood flow velocities and volumes. It can accurately identify stenoses, measure flow rates, and detect thrombus without radiation or contrast. It is often used for surveillance or as a first-line screening tool. However, it can be limited by vessel depth, patient body habitus, and operator experience. Crucially, it does not provide the detailed roadmap of the entire venous outflow to the heart that is necessary for planning an intervention, nor does it allow for immediate treatment.

Other imaging modalities are rated as Usually not appropriate for this specific scenario.

  • CTA extremity area of interest with IV contrast provides excellent anatomic detail but requires a significant intravenous contrast load, which is a concern in patients with end-stage renal disease. It also delivers a higher radiation dose (rated as Varies) compared to the targeted fluoroscopy (rated ☢☢☢, 1-10 mSv) and provides less dynamic flow information.
  • MRA extremity area of interest without and with IV contrast is generally avoided. Gadolinium-based contrast agents carry a risk of nephrogenic systemic fibrosis (NSF) in patients with severe renal impairment. While newer agents have a better safety profile, the risk is not zero. Furthermore, MRA is often susceptible to artifacts in the high-flow access environment.

Once you’ve decided on fluoroscopic fistulography, our protocol guide covers the technique, contrast, and reading principles: IR Central Venous Access (PICC, Tunneled, Port).

What’s Next After Fluoroscopic Fistulography? Downstream Workflow

The results of the fistulogram directly guide the subsequent steps, often within the same interventional radiology procedure.

If the study is positive for a significant stenosis: This is the most common finding. The interventional radiologist will typically proceed with percutaneous transluminal angioplasty (PTA). A balloon catheter is advanced across the narrowed segment and inflated to stretch the vessel open. If the vessel recoils or the result is suboptimal, a stent may be placed to hold it open. The patient can often use the access for dialysis that same day or the next.

If the study is positive for a non-occlusive thrombus: The thrombus is often associated with an underlying stenosis. Treatment involves addressing the stenosis with angioplasty, which may be sufficient to restore flow and resolve the clot. In some cases, pharmacologic (e.g., tPA) or mechanical thrombectomy may be performed to remove the clot before treating the underlying lesion.

If the study is negative: A technically adequate fistulogram that shows no significant stenosis or other anatomical abnormality is a rare but important finding. In this case, the cause of dysfunction may be related to arterial inflow issues not visualized, patient-specific factors like hypotension, or cannulation technique. The patient should be referred back to the nephrology and dialysis teams for a comprehensive re-evaluation of their clinical parameters and dialysis prescription.

If the study identifies central venous stenosis: This requires a more complex intervention, often involving high-pressure balloon angioplasty and stenting of the large central veins. This is a specialized procedure with different risks and outcomes compared to peripheral access intervention.

Pitfalls to Avoid (and When to Get Help)

Navigating dialysis access dysfunction requires careful coordination and attention to detail. Here are a few common pitfalls to avoid:

  • Ignoring Early Warning Signs: Do not wait for the access to thrombose completely. Declining flow rates and rising venous pressures are the key indicators to act upon. Early intervention has a much higher success rate.
  • Incomplete Physical Examination: Before ordering imaging, perform a thorough physical exam of the access. Palpate for the thrill along its entire length and listen for the bruit. A change in character (e.g., a high-pitched bruit) can help localize a stenosis.
  • Poor Communication with IR: Provide the interventional radiologist with all relevant clinical information, including the specific hemodynamic data from dialysis, the location of cannulation sites, and any prior interventions. This context is crucial for a successful procedure.
  • Confusing Dysfunction with Infection: While a dysfunctional access can become infected, do not assume signs of dysfunction are infectious without evidence like erythema, purulence, or systemic fever. Delaying a workup for dysfunction to give a course of antibiotics can lead to access loss.

If a patient presents with an absent thrill and bruit, escalate immediately for emergent thrombectomy evaluation, as this represents a different, more urgent clinical scenario.

Related ACR Topics and Tools

For a comprehensive overview of all clinical variants related to dialysis access imaging, please consult our parent guide. For specific questions about other scenarios or to explore the technical details of the recommended studies, the following resources are invaluable.

Frequently Asked Questions

Why not just start with a Duplex Ultrasound for every patient with suspected access dysfunction?

Starting with Duplex Ultrasound is a very reasonable and common strategy, as it is non-invasive and provides excellent functional data. However, if the clinical suspicion for a treatable stenosis is high based on clear hemodynamic trends, proceeding directly to fistulography can be more efficient. A fistulogram allows for both diagnosis and immediate treatment in a single session, preventing delays and potentially saving the access from thrombosis.

What defines a ‘significant’ stenosis on a fistulogram that requires treatment?

A stenosis is generally considered hemodynamically significant and warrants intervention if it causes a narrowing of the vessel lumen by more than 50%. However, the decision to intervene is also based on the clinical context. Even a less severe stenosis may be treated if it is associated with a clear drop in access flow, elevated venous pressures, or other signs of dysfunction.

Is there a role for CTA or MRA in this specific scenario?

For the initial workup of access dysfunction with declining flow, CTA and MRA are rated as ‘Usually not appropriate’ by the ACR. The primary reasons are the risks associated with contrast agents in renal failure patients (iodine for CT, gadolinium for MRI) and the fact that fistulography provides superior dynamic information and the ability to intervene immediately. CTA/MRA may have a role in complex cases, such as evaluating the central veins or arterial inflow when ultrasound and fistulography are inconclusive, but they are not first-line tests.

How soon after an angioplasty can the patient use their fistula or graft for dialysis?

In most cases, the access can be used for dialysis immediately after a successful angioplasty. The puncture sites from the fistulogram are typically small and heal quickly. The interventional radiologist will provide specific post-procedure instructions, but a primary goal of the intervention is to restore function for the next scheduled dialysis session.

What if the patient has a known allergy to iodinated contrast?

A known contrast allergy requires careful management. For patients with a mild allergy, a premedication protocol with corticosteroids and antihistamines is typically effective. For severe, anaphylactic allergies, alternative imaging like Duplex Ultrasound becomes the primary diagnostic tool. In some cases, carbon dioxide (CO2) can be used as an alternative contrast agent for the fistulogram, though image quality can be lower than with iodine.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026