An arteriovenous fistula (AVF) is an abnormal joining of an artery and a vein. If an AVF is affecting health, early treatment can help prevent complications.

An AVF occurs if an artery connects to a vein, rather than the capillaries. This abnormal connection can affect blood flow and pressure, which may cause serious problems without treatment.

An AVF may be present from birth, or occur through traumatic injury or blood vessel damage during a medical procedure. An AVF is also a common part of dialysis treatment to allow access to the blood vessels.

This article looks at symptoms, causes, diagnosis, treatment, and outlook for an AVF.

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An AVF is an abnormal connection between an artery and a vein.

Arteries carry blood away from the heart, while veins carry blood to the heart. Capillaries are small blood vessels that connect arteries and veins.

Normally, the arteries connect to capillaries, which connect to the veins. With an AVF, the artery connects directly to the vein, instead of through the capillaries. Depending on the size and location of the AVF, it may cause serious problems.

Blood pressure within the veins is lower than that in the arteries. When blood flows directly from an artery to a vein with an AVF, it alters the usual blood flow and pressure. This can cause problems, such as putting strain on the heart. In severe cases, an untreated AVF may lead to heart failure.

In some cases, a doctor may create an AVF in people with kidney failure to provide vascular access for dialysis. In these cases, an AVF can be an important part of treatment.

Otherwise, AVFs are rare and may be present from birth or occur through severe injury. AVFs can occur anywhere in the body. The location of an AVF may depend on the cause.

The symptoms of an AVF can vary depending on its location and cause.

AVFs in the arms or legs may present with:

If an AVF occurs in the brain, people may experience:

In some cases, an AVF may restrict blood flow to certain areas of the body. Symptoms of ischemia, or reduced blood flow, include:

If people have any symptoms of an AVF, they will need to contact a doctor.

Causes of an AVF include the following:

  • Dialysis: Creating an AVF is a common procedure for end-stage kidney disease to create long-term vascular access for dialysis. The AVF allows a large amount of blood to flow and pass through the dialyzer.
  • Medical injury: An AVF may occur due to some medical treatments, such as if surgery damages the blood vessels. This can happen with procedures such as heart catheterization or spinal surgery.
  • Traumatic injury: A penetrating injury that damages an area where an artery and vein are close together may cause an AVF. The most common cause of traumatic AVFs is gunshot wounds, but they may also occur with long bone fractures, skull fractures, or hyperextension injuries.
  • Congenital: Congenital AVFs are those present from birth. There is little understanding of them. They may occur due to injury, collagen disorders, blood vessel disorders, or a genetic disorder of the nervous system.

Risk factors for an AVF include:

  • medical procedures that may damage blood vessels, such as heart catheterization
  • chronic kidney disease, which may progress to kidney failure, in which people can require an AVF for dialysis
  • traumatic injury
  • previous injury affecting the blood vessels, which may cause an AVF at a later date

Researchers are unclear on the causes of congenital AVFs, so there is little understanding of possible risk factors for these.

A doctor may first take a medical history and carry out a physical examination to check for symptoms of an AVF.

The doctor can feel the area and use a stethoscope to listen to blood flow where the fistula may be, as an AVF can cause abnormal sounds or a murmur that sounds like machinery.

To confirm an AVF diagnosis, a doctor may carry out the following tests: Duplex ultrasound and angiography.

A duplex ultrasound uses sound waves to show blood flow in the arteries and veins. An angiography is an imaging test that combines either a CT or MRI scan with an injection of a contrast dye to show the blood vessels.

Doctors may also use a duplex ultrasound to assess the correct placement of an AVF for dialysis purposes.

If an AVF is not causing any symptoms or complications, or if the AVF is likely to resolve by itself, people may not need any treatment.

A person may need treatment for an AVF if it is causing problems, such as:

  • abnormal or unstable blood pressure
  • bleeding from a blood vessel
  • ischemia
  • congestive heart failure
  • difference in limb sizes
  • sores or ulcers that do not heal
  • impaired function

If an AVF is congenital, doctors may treat it as soon as they are aware, as it can cause problems later in life. Doctors can treat a dialysis AVF if it is no longer working or necessary.

Treating an AVF early may help to prevent complications. Doctors can use endovascular surgery to treat an AVF, or if this fails, open surgery.

Endovascular surgery is a minimally invasive surgery within the blood vessels. A doctor inserts a catheter into the blood vessels and uses a coil, tube, or cyanoacrylate glue to close the fistula.

Open surgery involves large incisions to access the blood vessels. A doctor may then close the fistula, repair or remove the damaged blood vessel, or create a bypass.

Endovascular surgery has fewer risks and less pain postsurgery and may result in quicker recovery with better outcomes than open surgery.

An AVF that is not causing any symptoms or problems may not need treatment, and people may only have to monitor for any changes.

Although some congenital AVFs can be life threatening, the overall outlook is positive. Around 15% of AVFs affect blood flow, whereas AVFs in peripheral areas usually do not.

If an AVF does need treatment, early diagnosis and treatment are essential to help prevent complications.

Doctors may stage AVFs from 1 to 4 to predict treatment success. A lower stage indicates milder symptoms and less severe complications. Ischemia occurs in stage 3, and heart failure in stage 4.

It may be possible to completely reverse decompensated or severe heart failure after treating an AVF, although the outlook is much better with early diagnosis and treatment.

An AVF is an abnormal connection between an artery and a vein, which can disrupt normal blood flow and blood pressure.

Some AVFs cause no symptoms or problems and may not need treatment. Others cause serious complications and require prompt treatment.

To treat an AVF, doctors may use endovascular surgery to close the fistula. Early treatment means the outlook for an AVF can be positive and it may prevent complications.