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What Is an AV Fistula?

AV Fistula RoomAn arteriovenous (AV) fistula is an abnormal connection between an artery and a vein. Normally, blood flows from your arteries into your capillaries—where nutrients and oxygen in your blood travel to tissues in your body—then into your veins.

When you have an AV fistula, blood flows directly from the artery into the vein, bypassing the capillaries. This causes the tissues that the capillaries normally feed to receive less blood supply. AV fistulas usually occur in the legs but can also develop in the brain, lungs or arms.

Leaving an AV fistula untreated can lead to serious complications. Small fistulas in your legs, arms, lungs or kidneys often won't have any symptoms and usually don't need treatment other than monitoring by your doctor. However, larger AV fistulas may cause symptoms including:

  • Swelling and reddish appearance on the skin’s surface
  • Purplish, bulging veins that you can see through your skin, similar to varicose veins 
  • Decreased blood pressure

An AV fistula in your lungs (a pulmonary arteriovenous fistula) is a serious condition that can cause:

  • Coughing blood
  • Difficulty breathing, especially when exercising
  • Nosebleeds
  • A bluish look to the skin
  • Clubbing of fingers (fingertips and fingernails spread out and become rounder)
  • Infections in your heart valves

What Causes an AV Fistula?

Causes of AV fistulas include:

  • Cardiac catheterization—An AV fistula can develop as a complication of a cardiac catheterization. During the procedure, a catheter is inserted in an artery or vein and threaded through the blood vessels. If the needle crosses an artery and vein, and the artery is widened (dilated), it can create an AV fistula. Although this is the most common way an AV fistula develops, it is still rare.
  • Injuries that pierce the skin—An AV fistula can also develop after a piercing injury, such as a gunshot or stab wound, if the wound is on a part of your body where a vein and artery are side by side.
  • Congenital anomaly—Doctors aren't sure what causes congenital AV fistulas, and being born with one is quite uncommon.
  • Genetic conditions—Pulmonary AV fistulas are usually caused by a genetic disease called Rendu-Osler-Weber disease, or ROWD. The disease causes blood vessels to develop abnormally, especially in the lungs.
  • Surgical creation—People who have late-stage kidney failure may have an AV fistula surgically created to make dialysis easier. If a dialysis needle is inserted into a vein too many times, the vein can scar and be destroyed. Creating an AV 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 more quickly.

How Is an AV Fistula Diagnosed?

To diagnose an AV fistula, 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. He or she may also use one of these diagnostic tests:

  • Doppler ultrasound—Doppler ultrasound is the most effective and common way to check for an AV fistula. It uses high-frequency sound waves to measure how fast blood flows.
  • Computerized tomography (CT) angiogram—A CT angiogram allows your doctor to check the artery he or she believes is narrowed to see if blood flow is bypassing the capillaries.
  • Magnetic resonance imaging (MRI)—Your doctor may use MRI if he or she thinks you have an AV fistula in an artery that’s deep under your skin.

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