An arteriovenous (AV) fistula is an abnormal connection between an artery and a vein. Normally, blood flows from your arteries to your capillaries to your veins. Nutrients and oxygen in your blood travel from your capillaries to tissues in your body.
With an arteriovenous fistula, blood flows directly from an artery into a vein, bypassing some capillaries. When this happens, tissues below the bypassed capillaries receive a diminished blood supply.
Arteriovenous fistulas usually occur in the legs, but can develop anywhere in the body. Arteriovenous fistulas are often surgically created for use in dialysis in people with severe kidney disease.
A large untreated arteriovenous fistula can lead to serious complications. Your doctor monitors your arteriovenous fistula if you have one for dialysis.
Small arteriovenous fistulas in your legs, arms, lungs, kidneys or brain often won't have any signs or symptoms and usually don't need treatment other than monitoring by your doctor. Large arteriovenous fistulas may cause signs and symptoms.
Arteriovenous fistula signs and symptoms may include:
An arteriovenous fistula in your lungs (pulmonary arteriovenous fistula) is a serious condition and can cause:
An arteriovenous fistula in your gastrointestinal tract can cause bleeding in your digestive tract.
If you have any of these signs and symptoms and think you might have an arteriovenous fistula, make an appointment to see your doctor. Early detection of an arteriovenous fistula may make your condition easier to treat and may reduce your risk of developing complications, such as blood clots or, in severe cases, heart failure.
Causes of arteriovenous fistulas include:
Cardiac catheterization. An arteriovenous fistula may develop as a complication of a procedure called cardiac catheterization. During cardiac catheterization, a long, thin tube called a catheter is inserted in an artery or vein in your groin, neck or arm and threaded through your blood vessels to your heart.
If the needle used in the catheterization crosses an artery and vein during your procedure, and the artery is widened (dilated), this can create an arteriovenous fistula. This rarely happens.
Surgical creation (AV fistula procedure). People who have late-stage kidney failure may have an arteriovenous fistula surgically created to make it easier to perform dialysis. If a dialysis needle is inserted into a vein too many times, the vein may scar and be destroyed.
Creating an arteriovenous fistula widens the vein by connecting it to a nearby artery, making it easier to insert a needle for dialysis and causing blood to flow faster. This AV fistula is usually created in the forearm.
To diagnose an arteriovenous fistula in your arms or legs, your doctor will use a stethoscope to listen to the blood flow through the area where he or she thinks you may have a fistula. The blood flow through an arteriovenous fistula makes a sound similar to clicking or humming machinery (machinery murmur).
If your doctor suspects a fistula, you'll have other tests to confirm your diagnosis. These can include:
Duplex ultrasound. Duplex ultrasound is the most effective and common way to check for an arteriovenous fistula in the blood vessels of your legs or arms. In duplex ultrasound, an instrument called a transducer is pressed against your skin over the suspicious area.
The transducer produces high-frequency sound waves, which bounce off red blood cells. A duplex ultrasound can estimate how fast blood flows by measuring the rate of change in its pitch (frequency).
Magnetic resonance angiography (MRA). Your doctor may use an MRA if he or she thinks you may have an arteriovenous fistula in an artery that's deep under your skin. This test allows your doctor to see the soft tissues in your body. It uses the same technique as magnetic resonance imaging (MRI), but also includes the use of a special dye that helps create images of your blood vessels.
During an MRI or MRA, you lie on a table inside a long tubelike machine that produces a magnetic field. An MRI machine uses the magnetic field and radio waves to create pictures of your body's tissues. Using the images from the test, your doctor may be able to see an arteriovenous fistula.
Left untreated, an arteriovenous fistula can cause complications, some of which can be serious. These include:
Beyond genetic or congenital conditions, your risk of developing an arteriovenous fistula may increase due to certain factors, including: