Arteriovenous fistula

An arteriovenous (AV) fistula is an abnormal gateway or passageway that connects artery and vein. In normal conditions, blood flows from the arteries to veins through capillaries. The capillaries supply blood to the tissues of the body. In the case of arteriovenous fistula, blood flows directly into the vein from the artery escaping the capillaries. This results in the lack of blood flow to the tissues below the capillaries.

AV Fistula Symptoms

Small AV fistula doesn't cause symptoms. However, larger arteriovenous fistulas cause symptoms such as:

  • Purplish, bulging veins
  • Hypotension
  • Fatigue
  • Swelling in the arms and legs

If there is pulmonary AV fistula, the skin becomes bluish; there will be clubbing of fingers and severe cough with blood in the sputum. If there is AV fistula in the gastrointestinal tract, you can observe bleeding in the tract.

In rare cases, a large fistula can divert blood flow from the affected area (usually arms or legs), making that area numb, painful, cramping, and bluish colored.

Causes

AV fistula may be congenital, which may be due to abnormal development of arteries and veins in the womb.

This condition can also be seen due to cardiac catheterization.The catheter has a tube-like structure and consists of the needle. It is inserted into an artery or a vein.During this procedure, the blood vessel may get dilated leading to the formation of an arteriovenous fistula. Injuries that pierce the skin can also cause this condition.

Certain genetic conditions such as hereditary hemorrhagic telangiectasia cause pulmonary AV fistula. In some cases, AV fistula is created through surgery to aid in dialysis.

Complications

AV fistula can rupture and cause subarachnoid hemorrhage. They may also result in blood clots (can cause pulmonary embolism) or heart failure. The heart pumps with increased intensity to compensate the fall in blood pressure. Due to this, the heart muscle weakens leading to heart failure, which is a life-threatening condition.

Your doctor observes blood flow at the suspected area with the help of a stethoscope as the blood flowing through a fistula makes a clicking sound. If the sound is heard, your doctor may recommend you to undergo imaging tests such as:

Duplex ultrasound: This test helps to detect fistulas in arms and legs. The test can estimate how fast the blood flows with the support of a transducer that produces high-frequency sound waves.

Magnetic resonance angiography: This test helps to detect fistulas between deeper arteries and veins. The procedure involves the use of a special dye to make the blood vessels more visible.

Computed tomography (CT) angiogram: This test helps to detect fistulas with the injection of a contrast dye to produce clear images of the blood vessels. The test helps your doctor to confirm the diagnosis.

In the case of pulmonary AV fistula, tests such as arterial blood gas, complete blood count, echocardiogram, chest X-ray, and pulmonary arteriogram are performed.

If the fistula is small and doesn’t have symptoms, your doctor monitors the fistula. If there are symptoms, then the treatment of choice would be catheter embolization. The process involves blocking the fistula with the help of a catheter. A catheter is inserted into the artery near the fistula, and the stent is placed at the fistula to restore normal blood flow.

Other procedures include:

Ultrasound-guided compression : If the fistula is clearly visible on ultrasound, your doctor may recommend this procedure. With the help of an ultrasound probe, your doctor compresses the fistula and restores the blood flow.
Surgery : If the fistulas are large and cannot be treated with catheter embolization, then your doctor recommends surgery. Surgery involves removal of the abnormal blood vessels.

These procedures require a skilled surgeon as the surgery is extensive and AV fistulas present near the major structures such as eye or brain are difficult to treat.