What is AV fistula? Why it is done?

An AV fistula, also known as arteriovenous fistula, is a  condition in which an artery and vein have an abnormal connection with each other. Normally, blood flows from your arteries to your capillaries, and then on to your veins. 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. This condition usually occurs in the legs, but it can develop in any part of the body. Sometimes, it is surgically created for the treatment of other conditions.

What is AV fistula?

An AV fistula is an unusual connection established, either naturally or artificially, linking an artery and a vein. Usually, blood flows from your arteries to your capillaries, and then into your veins. An AV fistula causes a direct flow of blood from an artery into a vein. As a result, less blood is sent to the tissues below the bypassed capillaries.

What Are The Symptoms Of AV fistula?

Small AV fistulas in your limbs, brain, lungs, or kidneys don’t usually show signs and rarely require any treatment. However, large fistulas cause visible signs and symptoms. They include:

• Bulging, purple veins. You can observe these veins running under your skin. They appear similar to varicose veins.
• Swelling in your limbs
• Fatigue
• Heart failure
• Low blood pressure

A large AV fistula located in your lungs, also called a pulmonary arteriovenous fistula, is a critical condition. The symptoms of this condition are:

• A shade of blue on your skin.
• Coughing up blood
• Clubbing of fingers (the fingers spread out and become abnormally round)

An arteriovenous fistula in your gastrointestinal tract may cause bleeding in the digestive tract.

When To Consult A Doctor?

If you have any slightest suspicion of having an AV fistula, especially after noticing symptoms specific to this condition, visit a doctor immediately. Early diagnosis and treatment can help in recovery without any serious complications. 

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What are the causes of AV fistula?

An AV fistula may be caused by:

• Genetic conditions: Pulmonary AV fistulas (an AV fistula in the lung) may be caused by a genetic disease called Osler-Weber-Rendu disease, otherwise known as hereditary hemorrhagic telangiectasia. This disease causes blood vessels to develop abnormally in the lungs.
• Congenital AV fistula: In some babies, the blood vessels fail to develop properly in the womb. In these cases, the baby is born with an AV fistula.
• Pierced skin caused by injuries: An AV fistula may develop as a result of a piercing injury. For instance, a stab injury or a gunshot wound on a part of your body where your veins and arteries run close together may lead to an AV fistula at the site.
• Dialysis-related surgery: Those who suffer fromlate-stage kidney failure may have a surgically created arteriovenous fistula in the forearm to make it easier for dialysis.

When Is An AV fistula Done Artificially?

Sometimes, an AV fistula is introduced into your body surgically to treat kidney failure in a procedure called hemodialysis.

Hemodialysis is a procedure that uses a machine to send your blood through a dialyzer outside the body. A surgically created fistula may be used to remove and return your blood during the procedure. Inside the dialyzer, wastes and extra fluid in the blood are removed through thin fibers that filter them out. The filtered blood is brought back to the body through another tube. An AV fistula allows large amounts of blood to flow continuously to filter as much blood as possible at a go. An AV fistula should be created before the first treatment.

An AV fistula is usually placed in the forearm or upper arm. This provides reliable access to the blood vessels. Without this access, hemodialysis would be impossible. When the session starts, two needles are inserted into the fistula. One carries blood from the body to the dialyzer while the other carries the filtered blood back to the body.

An AV fistula is suggested over the other types of access because it:

• Provides improved blood flow for hemodialysis.
• Is more reliable and durable compared to other types of access
• Is unlikely to get infected or cause problems compared to other types of access.

If you don’t have a vein of sufficient size for an AV fistula, an artificial vein may be fitted via AV bypass graft surgery. If dialysis is required immediate, a dialysis catheter can be inserted in a vein until a longer-term solution is created

How Is An AV fistula Diagnosed?

Initially, a doctor will listen to your blood flow using a stethoscope at the site of suspicion. An AV fistula produces a humming sound. To confirm the condition, the following tests are done:

• Duplex ultrasound: Sound waves are used to assess the blood flow. This test is the most effective way to diagnose AV fistula.
• CT angiogram: This test shows if your blood flow is bypassing the capillaries. You will receive an injection of a dye prior to the procedure. This is done to allow your arteries and veins to be displayed more clearly on the CT images.
• Magnetic resonance angiogram: This test is performed when the AV fistula is deep under your skin. A special dye is used in this procedure as well.

How is  an AV fistula treated ?

Sometimes, small fistulas close by themselves without any treatment. However, fistulas that have existed for a long time and are causing problems, must be attended to immediately .

• Ultrasound-guided compression: This treatment employs an ultrasound procedure and is commonly used when the AV fistula is in your leg. In this procedure, a probe is used to compress the fistula using ultrasound and block the flow of blood to the damaged blood vessels. This procedure only works for 1 in 3 people.
• Catheter embolization: Here, a catheter is inserted in an artery close to the fistula. X-rays and other images are used to guide the catheter to your AV fistula. Your blood flow is redirected using a small coil placed at the site of your fistula.
• Surgery: AV fistulas, especially large ones that cannot be treated with other methods may require surgery. The type of surgery needed depends on the location of your AV fistula.

Conclusion

Untreated AV fistulas may result in serious issues. Seek immediate medical help and cure yourself of this condition as early as possible. If you have a surgically placed AV fistula, your doctor will monitor it regularly.

Frequently Asked Questions (FAQs)

1. What are the types of arteriovenous fistula for dialysis?

There are three types of AV fistula for dialysis:

• Radiocephalic fistula: This is a forearm fistula
• Brachiocephalic fistula: This is an upper arm fistula
• Brachial artery-to-transposed basilic vein fistula (BTB): This is also an upper arm fistula. It differs from brachiocephalic fistula in the type of vein and artery that are fused.

2. What are the complications of AV fistula?

If this condition is left untreated, several complications may arise. Some of these complications are:

• Heart failure: This is the most dangerous complication of this condition. Blood flows quicker through an AV fistula than it does through normal arteries and veins. This causes the heart to pump faster and harder to compensate for the increased blood flow. The suddenly increased workload on your heart can interfere with normal cardiac functions, leading to heart failure.
• Blood clots: An AV fistula in your limbs, particularly your legs, may lead to blood clots, potentially causing deep vein thrombosis. Deep vein thrombosis may become a life-threatening condition if the clot reaches your lungs. It may also lead to a stroke.
• Bleeding in your gastrointestinal system: AV fistulas may cause bleeding in your digestive system.

3. What are the risk factors of AV fistula?

Some of the risk factors of AV fistulas are:

• The female sex
• Cardiac catheterization (a treatment for cardiac problems)
• Certain medications such as blood thinners and antifibrinolytics.
• Older age
• High BMI
• High blood pressure