Arteriovenous Graft Thrombosis

When an arteriovenous graft becomes blocked by a blood clot, it prevents patients from receiving life-sustaining dialysis treatment and can lead to the loss of this vital connection to their bloodstream.

Table of contents

• What is arteriovenous graft thrombosis?
• Affected body parts
• What causes thrombosis?
• How common is this problem?
• Warning signs and prevention
• Treatment options

What is arteriovenous graft thrombosis?

Arteriovenous graft thrombosis occurs when a blood clot blocks an arteriovenous graft (AVG), which is a soft synthetic tube placed between an artery and a vein to create an artificial high-flow blood vessel.^[1] This type of access is commonly used in patients with kidney failure who need hemodialysis, a treatment that uses a special machine to remove waste materials from the body when the kidneys can no longer do this job properly.^[2]

When blood does not flow smoothly through the graft, it can begin to coagulate, turning from a free-flowing liquid to a semi-solid gel called a thrombus or blood clot.^[3] When this happens, the graft becomes blocked and dialysis cannot be performed.

An arteriovenous graft is created by surgically connecting an artery and vein using polytetrafluoroethylene (PTFE) or other synthetic materials. The graft is tunneled under the skin to facilitate regular needle access for dialysis treatments.^[4] These grafts are typically tapered, ranging from about 4 millimeters at the connection to the artery to at least 7 millimeters at the connection to the vein.^[5]

Affected body parts

• Arteries (usually in the arm)
• Veins (usually in the arm)
• Blood vessels

Arteriovenous grafts are most commonly placed in the upper arm, connecting the brachial artery near the elbow to the axillary vein near the armpit.^[6] However, grafts can also be created in other locations depending on the patient’s blood vessel health and previous access sites.

What causes thrombosis?

The main cause of arteriovenous graft thrombosis is narrowing of the blood vessels, known as stenosis. When a vein and artery are connected through a graft, the vein is at risk for damage caused by changes in blood flow rate and pressure from the high-pressure, high-flow arterial system.^[7] Your body responds to this damage by sending extra cells to repair the problem, but these extra cells can build up over time and cause narrowing.

Stenosis is the number one cause of dysfunction in arteriovenous grafts and accounts for 65 to 85 percent of cases of permanent access loss.^[8] This narrowing usually develops gradually over time and most often occurs at the anastomosis, which is the surgical connection site where the graft meets the vein.^[9]

Additional factors that can contribute to thrombosis include inadequate arterial inflow to the graft. Arterial narrowing and calcification are relatively common in patients with chronic kidney disease, especially those with diabetes and hypertension.^[10] When stenosis develops and blood does not flow smoothly, blood clots can form and completely block the graft.

How common is this problem?

Approximately 430,000 patients in the United States are dependent on hemodialysis.^[11] Arteriovenous graft thrombosis occurs approximately 0.5 to 2.0 times per year in patients with grafts.^[12] This complication may lead to multiple missed dialysis sessions, hospital admission, and the need for placement of a temporary dialysis catheter.^[13]

Access thrombosis is a serious problem because it is the leading cause of permanent access loss, accounting for 65 to 85 percent of cases.^[14] As many as 25 percent of hospital admissions in the dialysis population have been attributed to problems with vascular access, including graft malfunction and thrombosis.^[15]

Warning signs and prevention

Many problems that affect an arteriovenous graft can be identified through regular monitoring using a “look, feel, and listen” approach.^[16] Physical examination should be performed at least monthly by a qualified healthcare provider and includes looking at, feeling, and listening to the access to identify possible narrowing that places the access at risk of thrombosis.^[17]

Signs that may indicate problems with your graft include increased pulsatility, which may be a sign of outflow stenosis. A discontinuous thrill (the vibration you normally feel over the graft) or a high-pitched sound when listening with a stethoscope in the outflow vein can also indicate narrowing.^[18] Additional warning signs include prolonged bleeding after needle removal, difficulty with needle placement during dialysis, and swelling in the arm.

Patients should be taught to examine their graft regularly to understand the feel of a healthy vibration and to look for any redness or swelling that indicates infection. This helps expedite treatment interventions to save the graft and avoid the need for surgery and potential loss of this valuable access site.^[19]

Blood flow through the graft can be assessed using duplex ultrasound, a relatively easy imaging test for superficial vascular grafts. Studies have shown that when access flow is measured repeatedly, trends of decreasing flow add predictive power for detecting narrowing.^[20]

Treatment options

When an arteriovenous graft becomes blocked by a clot, interventional radiologists use image-guided interventions to fix the problem. These minimally invasive procedures are performed to improve or restore blood flow in the graft.^[21]

Percutaneous treatment (through the skin) is generally preferred over surgical removal of the clot. Various approaches can be used, including:^[22]

• Catheter-directed thrombolysis, which dissolves blood clots that build up in grafts by injecting medicine through a thin tube
• Catheter-directed mechanical thrombectomy, where the clot is physically removed or broken up using devices inserted into the vein
• Angioplasty, which uses mechanical devices such as balloons to open the graft and help it remain open
• Vascular stenting, where a small wire mesh tube called a stent may be implanted to keep the graft open if angioplasty alone fails

The surgical approach for graft thrombosis involves making an incision and using a specialized catheter to remove clots from both the venous and arterial sides of the graft. Surgical repairs require general anesthesia, which may be a limiting factor in this patient population given the high incidence of other medical conditions.^[23]

The decision of whether to perform minimally invasive salvage or surgical intervention for a blocked graft depends on the expertise of the medical center and the specific characteristics of each case. When available, minimally invasive options are often preferred because they can be performed without general anesthesia and typically allow patients to return home the same day.^[24]

After treatment, ongoing monitoring and care of the graft remain important to detect and address any future problems before complete blockage occurs again.