Definition and Overview
An arteriovenous graft (AVG) is an artificial conduit that connects an artery to a vein. It is used as a substitute for a dialysis fistula in cases where an AV fistula cannot be made. Both are used for the dialysis procedure as the primary access through which blood is removed, filtered, and returned to the body. Thrombosis, on the other hand, is a medical term used to refer to the formation of blood cloth. Thus, an arteriovenous graft thrombosis is the formation of a blood clot inside the arteriovenous graft.
An AV fistula is made using the patient’s own arteries and veins to create a conduit for the dialysis procedure. This means no artificial material is used. Fistulas are highly effective and useful for long-term (even permanent) access, with a very low risk of complications. They can last for years and even decades with no problems.
However, although the best type of access is through AV fistula surgery, there are some cases wherein it is not possible to create a fistula for dialysis, which necessitates an artificial option, such as the use of a catheter or an AV graft.
An AV graft is a tube that the surgeon inserts underneath the skin. One end of the tube is connected to an artery while the other is connected to a vein. The graft can be either straight or shaped like a horseshoe. It can be placed either in the arm or the leg depending on the size and condition of the patient’s arteries and veins. Unlike a fistula that has to mature first before it can be used, an AV graft can be used as early as two weeks after placement. It is also ideal for patients with small or weak veins.
The use of an AV shunt for peritoneal dialysis is not without its complications, and one of the most common problems is the formation of blood clots. Unfortunately, the risk of blood clot formation is higher among those with an arteriovenous graft than those with an AV fistula. If the fistula or graft becomes blocked, the patient will not be able to undergo dialysis.
Causes of Condition
An arteriovenous graft thrombosis is one of the potential complications that may arise following the placement of an AV graft for dialysis. In some cases, the problem begins with graft stenosis, in which the graft becomes narrow. Once this occurs, the risk of thrombosis rises exponentially.
Various case studies show blood clots in a fistula or an AV graft are commonly caused by:
Tight fitting garments
Jewellery that may restrict blood flow especially if the AV graft access is placed on the arm
Sudden spikes in blood flow in the AV graft, such as when undergoing a blood pressure test
Pressure on the AV graft
Bumping the access arm
Patients with a dialysis shunt are advised to monitor the blood flow through their access tubes on a regular basis. When left untreated, repetitive blood clots can completely block the flow of blood through the AV graft and this can result in graft failure.
Symptoms of an arteriovenous graft thrombosis include a reduced amount of blood flowing through the tube. Normally, patients will feel the blood rushing through the tube as well as hear a rumbling sound. These are signs of good blood flow through the fistula or graft.
Patients who notice a difference in the motion of blood through the tube should see their doctor immediately. Any changes in the pitch or sound of the blood flowing through the tube, such as an abnormal whooshing or whistling sound, may indicate either a narrowing (stenosis) problem or a blood clot formation.
An arteriovenous graft thrombosis can also cause swelling and pain in the affected arm. Other symptoms of a blood clot include:
Cold hands and fingers
Paleness or discolouration of the hands and fingers
Sudden bulging around the graft
Fever and chills
Bleeding from the graft outside the dialysis unit that continues longer than 20 minutes despite applying pressure
Who to See and Types of Treatments Available
An arteriovenous graft thrombosis is a common problem faced by patients undergoing dialysis, especially since grafts are more easily blocked or obstructed compared to a dialysis fistula. Hence, there are a lot of declotting interventions, which can either prevent a clot from forming or remove a clot that has formed. Many of these procedures are now performed using minimally invasive methods.
In case a blood clot has formed in an AV graft, the patient will have to undergo treatment. Available treatments include:
Angioplasty and vascular stenting - Similar to surgery used to resolve blood clots and treat cardiovascular conditions, this procedure use a mechanical device, such as a balloon, to widen the AV graft tube and keep it open with a stent to restore normal blood flow.
Catheter-directed thrombolysis - This treatment involves dissolving the blood clots in the AV graft by injecting medications into the tube.
Catheter-directed mechanical thrombectomy - A minimally invasive procedure that removes or mashes up the blood clot using a catheter and special surgical tools.
Patients can also supplement any of the above procedure with blood-thinning medications that are helpful in keeping blood from clotting.
Following treatment for an arteriovenous graft thrombosis, patients may experience slight bruising and tenderness near the graft. This is normal but should resolve within a few days.
“Vascular Access for Hemodialysis.” National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/kidney-disease/kidney-failure/hemodialysis/vascular-access
“Some facts about the AV graft.” The Kidney Foundation of Canada. https://www.kidney.ca/document.doc?id=762
Trimmer C. “Dialysis Graft Interventions.” RadiologyInfo.org. https://www.radiologyinfo.org/en/info.cfm?pg=dialysisfistulagraft#overview
Mickley V. “Stenosis and thrombosis in haemodialysis fistulae and grafts: the surgeon’s point of view.” Nephrol Dial Transplant. 2004. 19(2):309-311. https://academic.oup.com/ndt/article/19/2/309/1863752/Stenosis-and-thrombosis-in-haemodialysis-fistulae