And it can affect various parts of the body, such as the extremities, the brain or the lungs. Treatment is usually only necessary if the arteriovenous fistula is large and causes symptoms or impairs the drainage of normal veins, particularly in the brain. Embolization, in which we close the fistula, is used most frequently. Sometimes an operation is necessary. Alternatively, radiosurgery – a high-dose radiotherapy in one session – can also be performed.
What is an arteriovenous fistula?
An arteriovenous fistula – like an arteriovenous malformation – is a short-circuit connection between an artery and a vein. The blood then does not flow out of the artery via the fine capillaries, but enters the draining vein at high pressure. The vessel is overloaded and can bulge. In addition, the tissue below the bypassed capillaries receives too little blood. In general, a fistula is an unnatural passage between organs, vessels or tissues that does not normally belong there.
In principle, an arteriovenous fistula can form anywhere in the body. However, it often affects the leg, sometimes also the meninges (dural arteriovenous fistula), the spinal cord (spinal AV fistula) or the lungs (pulmonary AV fistula). It can also be congenital (rare) or acquired in the course of life. The causes in the latter case are often damage to the vessel wall due to an injury (trauma), for example with a knife, or venous thrombosis (brain). Doctors also make use of such short-circuit connections in medical treatments, for example in blood washing (dialysis). The arteriovenous fistula has other names: AV fistula, arteriovenous shunt or AV shunt.
The symptoms of an arteriovenous fistula depend on how large it is and where in the body it has developed. Smaller AV fistulas often go unnoticed. If the short circuit is close under the skin, the fistula sometimes appears reddish-blue and swollen. A larger arteriovenous fistula can cause low blood pressure, tiredness and fatigue. An arteriovenous fistula in the brain can cause a cerebral hemorrhage. Unfortunately, the symptoms of even dangerous arteriovenous fistulas in the brain are often non-specific (headaches, tinnitus, fatigue, visual disturbances, epileptic seizures).
The AV fistula does not always need to be treated. Small fistulas between arteries and veins usually cause no symptoms. If impairments do occur, the unnatural connection is closed by embolization or removed during an operation.
Arteriovenous fistula – frequency and age
The frequency of arteriovenous fistula cannot be quantified. Only in rare cases is it congenital. Those affected usually acquire them in the course of their lives. Sometimes doctors create the artificial connection on purpose, for example for blood washing.
Congenital arteriovenous fistula naturally affects younger people. Otherwise, AV fistula can occur at any age.
Arteriovenous fistula: causes and risk factors
The causes of arteriovenous fistulas vary. Doctors usually divide them up like this:
- Injuries that damage the skin: Examples include trauma caused by a bullet or a knife thrust in an area of the body where arteries and veins run close together.
- Thrombosis: Dural arteriovenous fistulas of the hard meninges usually develop as a result of thrombosis. This is rarely noticed by the patient. During the thrombosis, small arteries sprout into the thrombus. If the thrombosis dissolves again, an arteriovenous fistula remains.
- Congenital AV fistulas: Babies are born with an arteriovenous fistula. It is not known why this unnatural connection forms during embryonic development. But there is an error in vascular development in the womb.
- Genes: The cause of arteriovenous fistulas in the lungs can be a genetic disease, for example Osler-Weber-Rendu disease (also known as hereditary hemorrhagic telangiectasia, abbreviated to HHT). The blood vessels throughout the body develop incorrectly. The vessels in the lungs are particularly affected.
- Blood washing (dialysis): People with end-stage chronic kidney disease are often dependent on dialysis. To facilitate dialysis, doctors create an artificial connection between a vein and an artery during an operation. They usually place the dialysis shunt in the forearm. The short-circuit connection establishes a sufficient blood flow and ensures rapid dialysis.
Risk factors for arteriovenous fistulas
There are also some risk factors that may favor arteriovenous fistulas. These include, for example:
- Diagnostic and therapeutic procedures such as cardiac catheterization – especially if the procedure involves the blood vessels in the groin
- Certain medications, for example blood thinners (anticoagulants) or antifibrinolytics, which inhibit the dissolution of fibrin and counteract blood loss.
- High blood pressure (hypertension)
- High body mass index (BMI) in the case of severe overweight andobesity
- Older age
Symptoms: Arteriovenous fistula often goes unnoticed
Arteriovenous fistulas do not necessarily cause symptoms. Smaller AV fistulas in the leg, arm, lungs, kidneys or brain often go unnoticed because they do not cause any symptoms. Doctors do not usually have to treat them, but only check them at regular intervals. The situation is different with larger arteriovenous fistulas or dangerous arteriovenous fistulas of the brain. They can cause the following symptoms, for example:
- Purple-colored, bulging veins that stand out under the skin and are easily visible from the outside – they look similar to varicose veins.
- Neurological symptoms: headaches, tinnitus, fatigue, visual disturbances, epileptic seizures
- Swelling in the arms or legs due to water retention (edema)
- Skin inflammation and ulcers if the fistula diverts a lot of blood from an arm or leg. This is also referred to as the tapping phenomenon. The blood flow in the extremity is reduced, resulting in reduced perfusion.
- Low blood pressure (hypotension): The vein walls bulge due to the increased arterial pressure because they cannot withstand it. The blood then flows more easily into these dilated veins and the blood pressure drops.
- Tiredness, fatigue, exhaustion due to low blood pressure
- Heart failure: The heart pumps harder and faster to compensate for low blood pressure. This strains the heart over time and can lead to cardiac insufficiency. In the long term, it can even lead to heart failure.
- Bleeding in the gastrointestinal tract if the AV fistula has formed in the digestive tract
A large arteriovenous fistula in the lung (pulmonary AV fistula) can be a very serious condition. Signs of this are the following complaints:
- Blue coloration of the skin (cyanosis) – the reason is a lack of oxygen
- Drum flail fingers – the end phalanges of the fingers thicken
- Hemoptysis
As a general rule, seek medical advice for any symptoms that seem unusual to you and that you cannot explain.
Arteriovenous fistula: diagnosis with us
The diagnosis of an arteriovenous fistula begins with a medical history interview. We will ask you a few questions to help us make an initial assessment. Examples are:
- What symptoms do you experience?
- When did the symptoms first start?
- How intense are they?
- Have you continuously increased or improved in between?
- In which part of the body are the symptoms noticeable?
- Do you have any known underlying diseases?
- Are there any diseases in your family?
- Have you recently suffered an injury, for example with a knife?
- Have you undergone a procedure in the past, such as a cardiac catheterization?
- Are you taking any medications? If yes: Which ones and since when?
This is usually followed by a physical examination. We feel the body with our hands and detect changes, such as thickened veins. We also examine the skin and look for abnormalities such as discoloration. We use a stethoscope to listen to the heart, the lungs or the blood flow in the arms and legs (auscultation). Sometimes unusual flow noises can be detected that sound like a humming or machine noise.
AV fistula: diagnosis using imaging techniques
If an arteriovenous fistula is suspected, we use imaging techniques. They show whether an arteriovenous fistula is actually present. The most important methods are
Arteriovenous fistula: prevention, early detection, prognosis
You cannot prevent a congenital arteriovenous fistula, which is due to an abnormal development in the womb. The same applies if the AV fistula occurs as part of a genetic disease, such as hereditary hemorrhagic telangiectasia.
You can protect yourself to a certain extent against some types of acquired AV fistula. Avoid violent confrontations of any kind and prevent possible injuries to the blood vessels (and other organs!). Always keep a wide berth around people who pose a threat of danger and could involve you in fisticuffs. There are no preventive measures for arteriovenous fistulas of the brain.
Special early detection measures for AV fistula in the doctor’s office are also not known. Therefore, always consult your doctor if you experience unusual symptoms for which you cannot find an explanation. And medical advice is required for injuries of any kind anyway. If the arteriovenous fistula is diagnosed early, it is often easier to treat. The risk of complications is also reduced, for example heart failure or cerebral hemorrhage.
If there are genetic diseases in your family, such as hereditary hemorrhagic telangiectasia (HHT), there are some measures for early detection for first-degree relatives. Arteriovenous fistulas can also be detected during these examinations.
Course and prognosis of arteriovenous fistula
The course and prognosis of an arteriovenous fistula depend on how large it is and whether it causes symptoms. Smaller AV fistulas usually cause no symptoms and do not require treatment. Larger, untreated fistulas between an artery and vein, on the other hand, can cause a number of complications. Arteriovenous fistulas on the brain are divided into dangerous (high risk of bleeding) and harmless (no risk of bleeding) according to a separate classification.
Complications of arteriovenous fistulas can be, for example
- Cerebral hemorrhage (with arteriovenous fistula on the brain)
- Heart muscle weakness (heart failure) – up to and including heart failure
- Blood clots (thrombosis), for example in the case of an AV fistula in the leg. This can also be life-threatening if the blood clot is carried into the lungs by the bloodstream and a pulmonary embolism occurs. If it reaches the brain, those affected suffer a stroke.
- Pain in the leg when a deep vein thrombosis (DVT) develops. Existing leg pain can also worsen
- Bleeding in the digestive tract if the AV fistula affects the gastrointestinal tract.
With treatment, the course and prognosis are good in most cases. Those affected can usually lead a completely normal life.
Arteriovenous fistula: treatment depending on extent
The treatment of an arteriovenous fistula depends on how large it is, whether it causes symptoms and where it has formed. We do not necessarily have to treat smaller AV fistulas. We only monitor and check the short circuit between the artery and vein at regular intervals. A small fistula sometimes closes by itself without treatment.
Arteriovenous fistulas on the brain are divided into dangerous (high risk of bleeding) and harmless (no risk of bleeding) according to a separate classification. The indication for treatment is based on this classification.
At the USZ, we treat younger patients as well as adults. Children are usually referred to us by the children’s hospital and return there after the intervention.
Details of the treatments