What Is an Arteriovenous Fistula?

An arteriovenous (AV) fistula is a connection between an artery and a vein. Normally, blood flows from the arteries to the capillaries then to the veins. With an AV fistula, blood will flow from an artery to a vein, bypassing some capillaries.

This can affect the tissues downstream from the bypassed arteries, causing them to receive less blood, or affect the veins and create swelling of an extremity. AV fistulas usually affect the legs, but they can occur anywhere throughout the body.

Often, AV fistulas are created surgically for patients who require dialysis. These are used as an access point to connect the patient to a dialysis machine.

Untreated, large arteriovenous fistulas can cause serious problems. Keep reading to learn more about AV fistulas, including the types, symptoms, causes, diagnosis, and treatment.

Types and Symptoms

Small AV fistulas occur in the legs, arms, lungs, gastrointestinal (GI) tract, or brain. They don’t always cause signs or symptoms, and may not need treatment other than monitoring. However, larger AV fistulas may cause symptoms.

AV Fistula of a Leg or Arm

AV fistulas commonly occur in a leg or arm. They are also surgically created in an arm for use in dialysis.

Symptoms of an AV fistula in a leg or arm might include:

• Purple, bulging veins that can be seen through the skin; may appear like varicose veins
• Swelling of the arms and legs
• Hypotension: Decreased blood pressure
• Heart failure signs: Shortness of breath with lying down and exertion, rapid or irregular heartbeat, persistent wheezing or cough, rapid weight gain, fluid retention

In addition to heart failure, large AV fistulas that are left untreated can lead to blood clots, leg pain, stroke, or bleeding.

Pulmonary AV Fistula

AV fistulas can also affect the lungs. A pulmonary arteriovenous fistula is a very serious condition.

Symptoms of this type of pulmonary AV fistula might include:

• Bloody sputum
• Problems breathing
• Difficulty with exercising
• Nosebleeds
• Shortness of breath with exertion
• Chest pain
• Cyanosis (blue skin)
• Finger clubbing

AV Fistulas of the GI Tract

AV fistulas also affect the gastrointestinal tract and cause bleeding there. These types of AV fistulas are rare.

Dural Arteriovenous Fistulas

Dural arteriovenous fistulas (DAVF) are abnormal connections between an artery and vein in the dura mater (tough covering) of the brain or spinal cord. These types of AV fistulas affect people later in life. They are not passed on genetically.

DAVFs usually involve large brain veins. They develop from narrowing or blockage in the brain’s venous sinuses. The venous sinuses are responsible for routing circulated blood from the brain back to the heart.

Most people do not have symptoms with a DAVF. If a person has symptoms, they are either benign or aggressive.

Benign symptoms might include:

• Hearing issues: Including pulsatile tinnitus (thumping or whooshing sounds in one or both ears)
• Vision problems: Including vision loss, eye bulge, swelling of the lining of the eye, eye palsies (limited eye movement), and cavernous sinus syndrome (headaches with tearing of the eyes, drooping eyelids, swelling and irritation of one or both eyes, vision loss or double vision, and inability to move the eye) 

Aggressive symptoms of a DAVF result from bleeding within the brain (intracerebral hemorrhage) or neurological effects caused by the DAVF.

Bleed in the brain can lead to sudden headaches with varying degrees of neurological disability. On the other hand, neurological deficits tend to develop gradually over days or months and will cause symptoms based on the location of the DAVF.

Aggressive symptoms might include:

• Seizures
• Speech and language difficulties
• Face pain
• Dementia
• Coordination problems
• Burning or prickling sensation
• Weakness
• Lethargy: Unrelenting exhaustion
• Apathy: Lack of interest or motivation
• Symptoms related to pressure from the bleed: Headaches, nausea, vomiting

Causes

AV fistulas are either congenital or acquired. Congenital means a person was born with the AV fistula. An acquired AV fistula is one that developed or was created after a person’s birth and/or later in life.

Congenital AV Fistulas

Congenital AV fistulas are rare. The exact reasons for why they might occur are unknown, but they may occur in some babies whose arteries and veins don’t develop correctly while in the womb.

Pulmonary AV fistulas can result from the abnormal development of blood vessels located in the lungs. These types of fistulas are also common in people with a condition called hereditary hemorrhagic telangiectasia (HHT). People with HHT have abnormal blood vessels in many areas of their bodies.

Acquired AV Fistulas

These are usually caused by some time of trauma. They can also be surgically created.

An injury that pierces the skin, such as a stab wound, can lead to an AV fistula in an area of the injury where the vein and artery are side-by-side. This type of fistula can appear right away or may develop after a few hours. The area will swell up if the blood makes its way into surrounding tissues.

A surgical AV fistula is a connection of an artery to a vein made by a vascular surgeon. The AV fistula is usually placed in the forearm (upper arm). Having a larger vein provides easy and reliable access to blood vessels.

The AV fistula is created for hemodialysis, an ongoing treatment that filters wastes and water from the blood in the same way healthy kidneys do.

Diagnosis

Your healthcare provider might suspect an AV fistula based on your symptoms. A large acquired AV fistula can cause what is called a machinery murmur. A medical professional can hear a sound similar to a moving motor when placing a stethoscope over the affected area.

Confirming an AV fistula requires imaging, including doppler ultrasonography, computerized tomography (CT) angiogram, and magnetic resonance angiography (MRA):

• Doppler ultrasonography is often used to confirm a diagnosis or rule out an AV fistula. It is one of the most effective and common ways to check for AV fistulas of the arms or legs. Doppler ultrasonography evaluates the speed of blood flow.
• CT angiogram is used to look at blood flow that is bypassing the capillaries. Before the test is started, you will be given an injection of a contrast dye that makes it easier for blood vessels to show up on the CT images.
• MRA is used if your healthcare provider thinks there is an AV fistula deep under the skin. Like magnetic resonance imaging (MRI), it uses a magnetic field and radio waves to take pictures of soft tissues. It is different than MRI because you are given a special dye that makes it easier to see blood vessels on images.

Treatment

Small AV fistulas usually don’t cause any problems. But your healthcare provider will want to monitor you to see if the AV fistula closes on its own. If you need treatment, your practitioner might recommend ultrasound-guided compression or catheter embolization:

• Ultrasound-guided compression compresses the AV fistula to block blood flow to the damaged blood vessels. According to the University of Pennsylvania Medical Center, this is a quick 10-minute procedure, but it only works for about one in three people.
• Catheter embolization involves inserting a catheter in the artery near the AV fistula site using imaging techniques, including ultrasound. A stent is placed at the AV fistula to reroute blood flow.

A Word From Verywell

Many AV fistulas will resolve on their own. However, larger ones need to be treated, or they can cause serious complications, such as stroke, heart failure, or neurological deficits. Fortunately, the prognosis can be positive once an AV fistula is treated.

If you experience symptoms of shortness of breath with exertion, problems with breathing, chest pain, severe headache, neurological problems, or other symptoms of any type of AV fistula, it is important to let your healthcare provider know right away. Prompt recognition and early treatment are important for a good outcome.