Types of AV Fistulas

An arteriovenous (AV) fistula occurs when a channel is formed between an artery and a vein. Veins carry blood toward the heart, and arteries carry blood away from the heart. A connection between an artery and a vein causes pressurized blood from the artery to flow into a lower-pressure vein. The result is that blood pressure drops, which causes the heart to pump faster. This puts increased strain on the heart, which can lead to heart failure if the fistula is large.

Congenital

• Some people are born with an AV fistula, although this condition is not common, according to the Merck Medical Library. A congenital AV fistula is usually small and will not create problems. Congenital AV fistulas usually appear near the surface of a patient's skin, creating a swollen reddish blue patch. They may also appear on the face, which will look like a bruise that never fades away. A large AV fistula will require surgery in order to eliminate the connection between an artery and a vein.

Surgical

• Sometimes arteriovenous fistulas will be created as part of medical treatment. Patients with damaged or no kidneys require kidney dialysis, a process that uses a machine in order to filter toxins out of a patient's blood. Every time dialysis is conducted, a vein must be pierced in order to circulate blood through the dialysis machine. If the same vein is pierced over time, the vein may become agitated, which will cause the vein to clot. Clotting can cause scar tissue to develop, which may kill off the vein. If this occurs, a surgeon will create an AV fistula, which connects the deadened vein to an adjacent artery or vein. Since veins cannot usually withstand the pressure from blood being pumped back into the patient from a dialysis machine, a doctor may create an artificial AV fistula to enlarge the vein. If a patient undergoing dialysis obtains a kidney donation, a surgeon will close off this artificial AV fistula.

Injury

• The third type of AV fistula develops during extreme physical trauma. A gunshot wound or a knife wound can cause internal scarring. If this internal scarring is extensive, a fistula between an artery and a vein may develop. This type of fistula can develop anywhere an individual has been injured, including the brain, face, legs, arms and trunk of the body. Trauma-based fistulas usually cause serious complications if they are not fixed. Doctors usually monitor a patient's blood pressure after trauma to ensure that an AV fistula has not developed.