An arteriovenous (AV) fistula is an abnormal connection between an artery and a vein. Normally, blood flows from your arteries to your capillaries, and then on 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 less blood.

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:

• Purplish, bulging veins that you can see through your skin, similar to varicose veins
• Swelling in the arms or legs
• Decreased blood pressure
• Fatigue
• Heart failure

A significant arteriovenous fistula in your lungs (pulmonary arteriovenous fistula) is a serious condition and can cause:

• A bluish tinge to the skin
• Clubbing of fingers (the fingertips spread out and become rounder than normal)
• Coughing up blood

An arteriovenous fistula in your gastrointestinal tract can cause bleeding in your digestive tract.

When to see a doctor

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. It also may reduce your risk of developing complications, including blood clots or heart failure.

Causes of arteriovenous fistulas include:

• Injuries that pierce the skin. An arteriovenous fistula may occur if you have a piercing injury, such as a gunshot or stab wound, on a part of your body where a vein and artery are side by side.
• Being born with an arteriovenous fistula (congenital). The exact reason why isn't clear, but in some babies, the arteries and veins don't develop properly in the womb.
• Genetic conditions. Arteriovenous fistulas in the lungs (pulmonary arteriovenous fistulas) can be caused by a genetic disease (Osler-Weber-Rendu disease, also known as hereditary hemorrhagic telangiectasia) that causes blood vessels to develop abnormally throughout your body, but especially in the lungs.
• Dialysis-related surgery. People who have late-stage kidney failure may have an arteriovenous fistula surgically created in the forearm to make it easier to perform dialysis.

In addition to certain genetic or congenital conditions, the following risk factors may make you more likely to develop an arteriovenous fistula:

• Being female
• Cardiac catheterization, especially if the procedure involves blood vessels in your groin
• Certain medications, including some blood thinners (anticoagulants) and medications used to control bleeding (anti-fibrinolytics)
• High blood pressure
• High body mass index (BMI)
• Older age

Left untreated, an arteriovenous fistula can cause complications, some of which can be serious. These include:

• Heart failure. This is the most serious complication of large arteriovenous fistulas. Blood flows more quickly through an arteriovenous fistula than it does through normal blood vessels. As a result, your heart pumps harder to make up for the increase in blood flow. Over time, the increased workload on your heart can interfere with how the heart works, leading to heart failure.
• Blood clots. An arteriovenous fistula in your legs can cause blood clots to form, potentially leading to deep vein thrombosis, a painful and potentially life-threatening condition if the clot travels to your lungs (pulmonary embolism). Depending on where your fistula is, it can lead to a stroke.
• Leg pain. An arteriovenous fistula in your leg can cause pain in your leg (claudication), or can worsen pain you already have.
• Bleeding. Arteriovenous fistulas may lead to bleeding in your gastrointestinal system.

Your doctor will use a stethoscope to listen to the blood flow in your arms and legs. The blood flow through an arteriovenous fistula makes a sound similar to humming.

If your doctor suspects a fistula, you'll have other tests to confirm your diagnosis. Tests to diagnose an arteriovenous fistula can include:

• Duplex ultrasound. Duplex ultrasound is the most effective and common way to check for an arteriovenous fistula in your legs or arms. In duplex ultrasound, sound waves are used to evaluate the speed of blood flow.
• Computerized tomography (CT) angiogram. A CT angiogram can show if blood flow is bypassing the capillaries. Before the test starts, you'll receive an injection of a dye (contrast) that makes your blood vessels show up more clearly on CT images.
• Magnetic resonance angiography (MRA). Your doctor may use this test if he or she thinks you have an arteriovenous fistula deep under your skin. Like an MRI, an MRA uses a magnetic field and radio waves to create pictures of the body's soft tissues. However, you're also given a special dye that helps create images of your blood vessels.

If your arteriovenous fistula is small and doesn't cause any other health problems, you may need only close monitoring by a doctor. Some small arteriovenous fistulas close by themselves without treatment.

If your arteriovenous fistula requires treatment, your doctor may recommend:

• Ultrasound-guided compression. This may be an option for you if you have an arteriovenous fistula in your legs that's easily seen on ultrasound. In this treatment, an ultrasound probe is used to compress the fistula and block blood flow to the damaged blood vessels. This procedure takes about 10 minutes. But it only works for about 1 in 3 people.
• Catheter embolization. In this procedure, a catheter is inserted in an artery near the arteriovenous fistula. Doctors use X-rays and other images to guide the catheter to your fistula. Then, a small coil or stent is placed at the site of your fistula to reroute your blood flow. Many people who have catheter embolization stay in the hospital for less than a day and can resume daily activities within a week.
• Surgery. Large arteriovenous fistulas that can't be treated with catheter embolization may require surgery. The type of surgery you'll need depends on the size and location of your arteriovenous fistula.

If you think you may have an arteriovenous fistula, make an appointment with your primary care doctor. You may be referred to a blood vessel (vascular) specialist or heart specialist (cardiologist).

Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to be prepared for your appointment. Here's some information to help you get ready for your appointment, and know what to expect from your doctor.

What you can do

• Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance, such as restrict your diet. Since tests for an arteriovenous fistula usually include an ultrasound, it's possible you'll need to fast for several hours before your appointment.
• Write down any symptoms you're experiencing, including any that may seem unrelated to an arteriovenous fistula.
• Write down key personal information, including previous piercing injuries or a family history of arteriovenous fistula or other blood vessel diseases.
• Make a list of all medications, vitamins or supplements that you're taking.
• Take a family member or friend along, if possible. Sometimes it can be difficult to recall all of the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. For arteriovenous fistula, some basic questions to ask your doctor include:

• What's the most likely cause of my symptoms?
• Are there any other possible causes for my symptoms?
• What kinds of tests will I need?
• What treatments are available, and which do you recommend?
• What's an appropriate level of physical activity?
• I have other health conditions. How can I best manage these conditions together?
• Should my children or other biological relatives be screened for this condition?
• Are there any brochures or other printed material that I can take home with me? What websites do you recommend visiting?

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

• When did you first begin experiencing symptoms?
• Have your symptoms been continuous, or do they come and go?
• How severe are your symptoms?
• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?