# Dialysis Access Stenosis: Angioplasty and Stent Grafts

## Introduction

**Stenosis** is the most common cause of dialysis access dysfunction and the primary precursor to thrombosis. Regular surveillance and timely treatment of hemodynamically significant stenoses preserve access function and reduce thrombosis events. **Percutaneous transluminal angioplasty (PTA)** is the mainstay of treatment, with **stent grafts** reserved for specific indications including recurrent or refractory stenoses.

## Pathophysiology of Access Stenosis

**Neointimal hyperplasia** is the predominant mechanism: smooth muscle cell proliferation and extracellular matrix deposition. Occurs most commonly at sites of **turbulent flow**: venous anastomosis (AVGs), juxta-anastomotic region (AVFs), swing point of grafts. **Central venous stenosis** results from prior catheter-related endothelial injury, typically in the subclavian or brachiocephalic veins. Wall shear stress, surgical trauma, and repetitive cannulation contribute to progressive narrowing. Lesions are progressive; untreated stenosis > 50% with hemodynamic significance leads to thrombosis.

## Clinical Detection of Stenosis

### Surveillance Methods

**Physical examination**: diminished thrill, pulsatile access, prolonged bleeding after needle removal, arm edema. **Access flow monitoring**: flow rate < 600 mL/min (AVF) or < 600 mL/min (AVG) suggests significant stenosis. **Venous pressure monitoring**: elevated dynamic or static venous pressures during dialysis. **Ultrasound dilution**: detects declining access flow over serial measurements. **Duplex ultrasound**: directly visualizes stenoses and measures peak systolic velocity ratios (PSV ratio > 2:1 indicates > 50% stenosis).

### Indications for Intervention

**> 50% stenosis** with associated clinical or hemodynamic abnormality. Declining access flow, elevated venous pressures, inadequate dialysis clearance. Prolonged bleeding post-cannulation, arm or hand swelling, difficulty with cannulation. Do **not** treat stenoses that are asymptomatic and hemodynamically insignificant.

![Dialysis access stenosis detection and surveillance algorithm](images/access-stenosis-surveillance.png)

## Angioplasty Technique

### Standard Balloon Angioplasty

Access the fistula or graft under ultrasound guidance; perform diagnostic fistulography. Identify all significant stenoses from anastomosis to central veins. Select balloon diameter based on the **adjacent normal vessel size** (typically 6-8 mm for forearm, 8-10 mm for upper arm AVFs; matched to graft diameter for AVGs). Inflate at **rated burst pressure** or higher using high-pressure or ultra-high-pressure balloons. Hold inflation for **1-2 minutes** to achieve optimal remodeling. Residual stenosis **< 30%** is the goal for technical success.

### Specialized Balloons

| Balloon Type | Pressure Rating | Mechanism | Indication |
|-------------|----------------|-----------|------------|
| Standard high-pressure | 20-30 atm | Radial force dilation | First-line for most stenoses |
| Ultra-high-pressure | 30-40 atm | Maximum radial force | Resistant fibrous stenoses |
| Cutting/scoring | Variable | Controlled intimal incisions | Resistant elastic recoil lesions |
| Drug-coated (DCB) | Standard | Paclitaxel inhibits neointimal hyperplasia | Recurrent AVF stenoses |

**High-pressure balloons** (rated to 20-30 atm): for resistant or fibrous stenoses. **Cutting/scoring balloons**: create controlled intimal incisions to facilitate dilation of resistant lesions. **Drug-coated balloons (DCBs)**: paclitaxel-coated; emerging evidence supports improved patency in AVF stenoses. **Ultra-high-pressure balloons**: for extremely resistant stenoses unresponsive to standard high-pressure balloons.

## Stent and Stent Graft Indications

### When to Use Stent Grafts

**Elastic recoil**: > 30% residual stenosis immediately after adequate angioplasty. **Vessel rupture**: covered stents (stent grafts) for extravasation during angioplasty. **Rapidly recurrent stenosis**: stenosis requiring intervention every < 3 months despite adequate angioplasty. **Venous anastomotic stenosis in AVGs**: stent grafts (e.g., **Flair, Gore Viabahn**) have demonstrated improved patency versus angioplasty alone.

### Central Venous Stenosis

**Bare metal stents or stent grafts** for symptomatic central venous stenosis (subclavian, brachiocephalic, SVC). **Wallstent** and **Viabahn** are commonly used; size to the normal adjacent vessel. Avoid stents at the **venous thoracic outlet** due to risk of compression and fracture. Treat concurrent peripheral stenoses in the same session.

![Stent graft placement indications and device selection](images/stent-graft-indications.png)

## Drug-Coated Balloon Technology

**Paclitaxel-coated balloons** inhibit neointimal hyperplasia at the treatment site. Evidence from randomized trials shows improved 6-month and 12-month target lesion primary patency. Most studied in **AVF juxta-anastomotic and outflow stenoses**. May reduce the frequency of re-interventions compared to standard PTA. Cost-effectiveness data are evolving; currently not universally adopted.

## Complications

**Vessel rupture**: 2-5% incidence; managed with prolonged balloon tamponade or covered stent placement. **Thrombosis**: can occur during or after intervention; treat with thrombectomy if needed. **Residual or recurrent stenosis**: the most common long-term issue; planned surveillance mitigates impact. **Access site hematoma**: manual compression and post-procedure monitoring. **Stent migration or fracture**: uncommon with modern devices; avoid high-mobility locations.

## Outcomes

**Technical success** of PTA: > 95% for most stenoses. **Primary patency** at 6 months: 40-60% for standard PTA; improved with DCBs and stent grafts. **Assisted primary patency** at 12 months: 70-85% with surveillance and re-intervention. Stent grafts at the venous anastomosis of AVGs: improved primary patency compared to PTA alone (RENOVA, REVISE trials). Central venous stents: variable patency; depends on location and etiology.

![Angioplasty and stent graft outcomes comparison chart](images/angioplasty-outcomes.png)

## Key Clinical Pearls

Neointimal hyperplasia is the dominant pathology; stenosis is progressive and requires ongoing surveillance. Angioplasty is the first-line treatment; reserve stent grafts for elastic recoil, rupture, and rapidly recurrent stenoses. Drug-coated balloons show promise in improving patency, particularly for AVF stenoses. Central venous stenosis often results from prior catheter use and may require stent placement. Assisted primary patency through surveillance and timely re-intervention is the key outcome metric.

## References

1. Haskal ZJ, Trerotola S, Dolmatch B, et al. Stent Graft versus Balloon Angioplasty for Failing Dialysis-Access Grafts (RENOVA). *New England Journal of Medicine*. 2010;362(6):494-503.
2. Trerotola SO, Lawson J, Roy-Chaudhury P, et al. Drug-Coated Balloon Angioplasty in Failing AV Fistulas: A Randomized Controlled Trial. *Clinical Journal of the American Society of Nephrology*. 2018;13(8):1215-1224.
3. National Kidney Foundation. KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update. *American Journal of Kidney Diseases*. 2020;75(4 Suppl 2):S1-S164.
4. Beathard GA, Litchfield T. Effectiveness and Safety of Dialysis Vascular Access Procedures Performed by Interventional Nephrologists. *Kidney International*. 2004;66(4):1622-1632.