Definition: what is an AV fistula?
The term "AV fistula" is an abbreviation for the expression arteriovenous fistula. It describes a direct short-circuit connection between an artery and a vein.
Normal blood flow takes place from the heart via the arteries to the smallest blood vessels in the individual organs and from there via the veins back to the heart. An AV fistula connects directly to blood flow from the artery to the vein.
Most AV fistulas are artificially made, for example for dialysis treatment. There are also pathological AV fistulas that are usually the result of a blood vessel injury, for example during a cardiac catheter examination. AV fistulas can also be congenital. Possible locations here are the groin region, the brain or the spinal cord. Since the pathological AV fistula leads to a disruption of normal blood flow, it may have to be surgically removed.
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Therapy of AV fistulas
The treatment of an AV fistula depends on the one hand on where it is located in the body and on the other hand whether and to what extent it leads to discomfort or stress for the patient. Smaller superficial arteriovenous fisteles can often be treated with a pressure bandage. This is intended to ensure that the vascular connection closes again spontaneously. However, surgical or interventional therapy is often required to treat an AV fistula.
If this is located in the brain, for example, a small platinum coil can be inserted into the fistula through a catheter pushed into the blood vessels. This ensures that the vascular connection closes. Such a procedure is called embolization. Another method to embolize an AV fistula is the injection of certain substances. This is also done through a vascular catheter that is specifically advanced. If embolization is not possible or there are reasons that speak against such a procedure, the treatment of an AV fistula can only be carried out with a vascular surgical operation. The vascular connections are usually loosened with a scalpel or laser beam and the blood vessels are tied off or closed. Depending on where the AV fistula is, how big it is and how much blood is flowing through it, this can be a minor intervention or a complex operation.
This is the prognosis for an AV fistula
The prognosis in the presence of an AV fistula depends essentially on the general condition and the accompanying illnesses of the patient. If a fistula that needs treatment is diagnosed and treated in good time, the prognosis is often good. However, the outlook for therapy is heavily dependent on the organ or region of the body in which the AV fistula is located.
The prognosis for an artificially created AV fistula, for example for dialysis, is often limited due to the kidney dysfunction and the often simultaneous restriction of other organs compared to healthy people. Nevertheless, many people can live with an AV fistula for many years, even if they are on dialysis. In some cases, a kidney transplant can even eliminate the need for dialysis, so the prognosis can be very good.
Symptoms of an AV fistula
Since an AV fistula can basically occur in any region of the body, there are also a large number of possible symptoms that can indicate this.
In general, the AV fistula can cause pain or a feeling of pressure. Special symptoms can show up, for example, with an AV fistula in the brain. Some patients experience noise in their ears caused by the flow.
If the AV fistula is located in a brain region behind the eye, the eyeball may pulsate and protrude (exophthalmos). It is also possible that the AV fistula will put pressure on a cranial nerve, which can result in various failures. Examples of this are visual disturbances such as double vision up to paralysis of the eye movement.
Localization of various AV fistulas
AV fistula in the groin
The AV fistula in the groin is a pathological short-circuit connection between the inguinal artery and vein. In rare cases, the disorder is congenital.
It is more often the result of an injury to the blood vessels, for example during a cardiac catheter examination of the groin.
There may be swelling and pain in the groin. Since the blood vessels involved are large, another possible consequence of an AV fistula in the groin is a noticeable increase in stress on the heart. This is because the blood only has to overcome resistance through the fistula and flows directly back to the heart.
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AV fistula in the brain
An AV fistula in the brain is usually a so-called carotid sinus cavernosus fistula. This is an acquired pathological connection between the carotid artery and the blood-draining sinus cavernosus in the skull. There are two different forms.
The direct fistulas are the result of an injury with a fracture of the skull base or a tear in a vascular sac in the artery (cerebral aneurysm). In this form, there is high blood flow between the vessels.
An indirect fistula, on the other hand, usually develops spontaneously as a result of vascular diseases or sinus infections. These are rather small connections between branches of the artery and the sinus through which only small amounts of blood flow. The direct AV fistulas with high blood flow and flow reversal into the sinus system are therefore particularly relevant. The result can be a reduced blood supply to the cerebral vessels, which can lead to deficiency symptoms such as impaired vision, dizziness or impaired consciousness
AV fistula in the spinal cord
An AV fistula in the spinal cord is a rather rare disease, which, however, undetected and untreated, can lead to paraplegia in the worst case. The cause is usually an acquired misconnection between a small artery in the hard skin of the spinal cord and a vein in the spinal cord. The resulting increased pressure in the venous system can lead to slowly progressive damage to the spinal cord.
The first symptoms can be signs of paralysis for which no other cause can be found, such as a herniated disc. The diagnosis can best be made with magnetic resonance imaging, but it is often not possible to determine it with certainty. The treatment of an AV fistula in the spinal cord can be carried out using a vascular catheter. The earlier the disease is recognized and treated, the better the prognosis.
AV fistula in the kidney
An AV fistula of the kidney is a direct pathological connection between the blood-supplying renal artery and the blood-evacuating renal vein. In one of four cases this is congenital, in the other cases it is the result of an injury, inflammation or medical intervention such as an operation.
The AV fistula often causes no symptoms. In some cases, however, you experience increased blood pressure, flank pain or bloody urine. In addition to an ultrasound examination, a computed tomography of the abdomen and an image of the vessels (angiography) are usually carried out for the diagnosis.
The AV fistula of the kidney is usually treated by closing it using a vascular catheter that is advanced through the inguinal vessels. In some cases, however, surgery may require some or all of the kidney to be removed. Since the kidneys are one of the organs with the most blood supply, life-threatening internal bleeding can occur without treatment.
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This is how AV fistulas are diagnosed
An imaging examination of the blood vessels is required to diagnose an AV fistula.
There are different methods for these so-called angiographies, such as DSA (digital subtractiosangiography), in which X-rays are used to visualize the vessels. An alternative is MR angiography (magnetic resonance), which works without X-rays or other ionizing radiation. In both procedures, a contrast agent must be introduced into the bloodstream.
In addition, the diagnosis can also be made with a special ultrasound examination if necessary. The so-called Doppler effect can even measure and determine the pathological blood flow typical of an AV fistula. Another easy way to detect a possible AV fistula is to have your doctor listen to it with a stethoscope. Superficial AV fistulas, such as those in the groin, can be noticed by a characteristic flow noise. However, at least one of the imaging methods mentioned must still be carried out in order to be able to make a diagnosis.
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Causes of an AV fistula
A distinction is made between three different forms of development for the causes of an AV fistula.
- On the one hand, it can be a congenital malformation which may only become noticeable after many years or which never causes symptoms. It can then be determined, for example, as a chance finding during an imaging examination.
- Another form of AV fistula is the artificially created connection of an artery and vein for dialysis treatment (blood washing) in the case of severe kidney dysfunction. This vascular connection is usually also referred to as a dialysis shunt. This is applied to ensure the high blood flow required for dialysis.
- The third type of AV fistula are the acquired forms. These are usually the result of an injury or a vascular disease. For example, an AV fistula in the brain can be the result of a fracture of the skull base caused by a serious accident. AV fistulas in the groin are, in most cases, the result of a medical intervention injury. If a cardiac catheter is advanced via the inguinal artery, the vascular wall can be injured, which leads to the formation of an AV fistula.
AV shunts during dialysis
Dialysis ("blood washing") is a kidney replacement procedure that is used in severe kidney dysfunction. At each treatment appointment, a vascular access must be made by puncturing a vein. This can easily cause inflammation of the blood vessel and clots can form. Ultimately, scarring can occur, which leads to a loss of function of the vein.
These consequences are prevented with dialysis by creating an arteriovenous fistula by means of a vascular surgery. For this purpose, a connection is usually made on the arm between an artery and an adjacent vein. This causes the vein to expand and increase blood flow. The blood vessel can now easily be pierced with the needle during each dialysis treatment. Because of the faster blood flow, blood clots will not form as quickly.
Nevertheless, the artificially created AV fistula (usually referred to as a shunt) can close over time or become inflamed due to the repeated punctures. In this case, a different artery and vein may need to be used to create a new AV fistula for dialysis.
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AV fistula after a cardiac catheter
The development of an AV fistula after a cardiac catheter is a typical complication that occurs in about one in a hundred cases.
During the procedure, the cardiac catheter is usually inserted through a puncture into one of the two inguinal arteries and advanced to the coronary arteries. Alternatively, access is via an artery on the arm. It can happen that the vessel wall is pierced by the inserted instrument and the adjacent, thinner-walled vein is also injured. This leads to a direct flow of blood from the blood-carrying artery and the blood-discharging vein, bypassing the deeper body regions and smaller blood vessels.
The resulting connection does not heal by itself due to the high pressure of the blood flowing through it but remains in place. In order to identify a possible AV fistula after a cardiac catheter at an early stage, the doctor will examine the groin region (or the arm) after the procedure. The presence of an AV fistula can often already be determined by palpation and listening with the stethoscope. An imaging examination can be used to decide whether the AV fist needs to be removed by further intervention.
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