Arteriovenous fistula or AV fistula is an abnormal connection between arteries and veins. It can occur at any point in the body, be of any size, and vary in length and number. It refers to both the surgical procedure done for dialysis and a symptom of disease or trauma.
Definition & Facts
Normally blood flow begins in the arteries and travels to the veins through the capillaries, whereas AV fistulas bypass the capillaries. This can result in reduced blood supply to the tissues. AV fistula can also be created surgically and used during dialysis for people with kidney failure. Dialysis requires access to the cardiovascular system and over half of the people who need it use AV fistulas, which creates a larger and tougher blood vessel that can tolerate multiple needle punctures needed for dialysis. AV fistula, whether created surgically or caused by disease or trauma, should be monitored carefully since it can lead to severe complications.
Symptoms & Complaints
- Pain in the arms and leg pain which may lead to swelling.
- Low blood pressure: Because of the decrease in blood volume, blood pressure also falls
- Bulging veins that look like varicose veins and with a purple hue.
- Deep vein thrombosis: This may be potentially caused by blood clots which can cause a life-threatening condition if the clot travels to the lungs.
- Skin turning blue (cyanosis)
- Clubbed fingers
- Coughing blood which indicates blood in the lungs
- Abnormal blood vessels (also called telangiectasias) on the skin or mucous membranes
- A large fistula may divert a lot of blood to cause symptoms of reduced blood flow in the affected arm or leg, causing subclavian steal syndrome
AV fistula can be caused by a variety of factors such as:
- Surgically: They are intentionally created for dialysis to make blood flow easily. They are usually done on the forearm.
- Congenital disorder: Arteries and veins for some unclear reason may not develop fully in the womb. A child is thus born with the condition. These usually don't require any treatment only monitoring since they heal on their own.
- Cardiac catheterization: This is a procedure where a catheter is inserted into the body via a vein or artery. If the long thin tube used crosses a vein and an artery an AV fistula will be formed.
- Genetics: A hereditary disease, Osler-Weber-Rendu syndrome commonly known as hereditary hemorrhagic telangiectasia (HHT) causes abnormal blood vessel development. This occurs throughout the body especially in the lungs causing pulmonary AV fistula.
- Skin injury: If an injury pierces skin occurs at the point where a vein and artery are next to each other, an AV fistula may form.
Diagnosis & Tests
When blood flows through an AV fistula it makes a humming or click sound known as a murmur. Diagnosis is done by using a stethoscope to listen to the blood flow on the suspected area and detect a murmur. Early detection makes the condition easier to treat and reduces the risk of complications developing. Once confirmed, additional tests are done to verify its existence. These tests might include:
- Complete blood count (CBC): This is used to measure the number of red blood cells and white blood cells, total amount of hemoglobin, average red blood cell size and platelet count.
- CT Angiogram: A dye-like substance is injected in the body and a CT scan takes images of the suspected arteries and can show if blood flow is bypassing any capillaries.
- Duplex ultrasound: Transducer that produces high-frequency sound waves is pressed over the suspected area. Speed of blood flow is then measured against the rate of change in frequency.
- Magnetic Resonance Angiography (MRA): This method is used if an AV fistula is suspected in an artery deep inside the skin.
Treatment & Therapy
Depending on the size of the AV fistula, various forms of treatment can be recommended. When small, they don't cause health problems and a doctor may suggest monitoring. However, treatment may include:
- Ultrasound-guided compression: This is a simple procedure carried out in 10 minutes and done when the AV fistula can be easily seen on ultrasound. The fistula is compressed by the ultrasound probe and blood flow to the damaged blood vessels is blocked. Unfortunately it only works in one out of three people.
- Catheter embolization: This involves inserting a catheter in an artery that's close to the AV fistula. An X-ray and other imaging techniques then guide the catheter to the fistula and a small coil or plug is placed there to reroute blood flow. It is a short procedure that may only require an overnight stay in hospital.
- Surgery: This is the last resort and used to treat fistulas that can't be treated using other methods. The type of surgery depends on location and size of the fistula.
Prevention & Prophylaxis