Definition: What is an AV fistula?

The term "AV fistula" is an abbreviation for the term arteriovenous fistula. It refers to a direct short circuit connection between an artery and a vein. Normal blood flows from the heart, through the arteries, to the smallest blood vessels in the individual organs, and from there back to the heart via the veins. An AV fistula leads to a direct blood flow from the artery into the vein via a connection.

Most AV fistulas are manufactured artificially, for example for dialysis treatment. In addition, there are morbid AV fistulas, which are usually the result of a blood vessel injury, for example in the context of a cardiac catheterization. In addition, AV fistulas can also be innate. Possible localizations here are the inguinal region, the brain or the spinal cord. Since the pathological AV fistula leads to a disruption of the normal blood flow, it may need to be surgically eliminated.

Therapy of AV fistulas

The treatment of an AV fistula depends first on where in the body it is and on the other hand on whether and to what extent it leads to discomfort or stress for the patient. Smaller superficial arteriovenous fistulae can often be treated with a compression bandage. This is to achieve that the vascular connection closes spontaneously again. Often, however, surgical or interventional therapy is needed to treat AV fistula.

For example, if it is localized in the brain, a small platinum spiral can be inserted into the fistula through a catheter inserted into the blood vessels. This ensures that the vascular connection closes. Such a procedure is called embolization. Another method to achieve embolization of an AV fistula is the injection of certain substances. This is also done by a targeted advanced vascular catheter. If embolization is not possible or if there are reasons to object to such a procedure, treatment of AV fistula can only be done with a vascular surgery. The vascular connections are usually dissolved by means of a scalpel or laser beam and the blood vessels are prevented or closed. Depending on where the AV fistula is located, how tall it is and how much blood flows through it, this can be a minor procedure 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 comorbidities of the patient. If a treatment-requiring fistula is diagnosed and treated in good time, the prognosis is often good. However, the outlook for therapy depends strongly on the organ or region of the body where the AV fistula is located.

The prognosis for an artificially created AV fistula for dialysis, for example, is often limited due to the renal dysfunction and a common simultaneous restriction of other organs to healthy people. Nevertheless, many people can live many years even with dialysis with an AV fistula. In some cases, a kidney transplant may even eliminate the need for dialysis so the prognosis can be very good.

Symptoms of AV fistula

Because an AV fistula can generally occur in any body region, there are also a variety of possible symptoms that may indicate this. Generally there may be pain or a feeling of pressure through the AV fistula. Special symptoms can be seen in an AV fistula in the brain, for example. Some patients feel a flow-induced ear noise. If the AV fistula lies in a region of the brain behind the eye, it can cause pulsation and protrusion of the eyeball (exophthalmos). It is also possible that the AV fistula causes pressure on the cranial nerve, which can result in various failures. Examples include visual disturbances such as double images up to the paralysis of eye movement.

Localization of different AV fistulas

AV fistula in the groin

The AV fistula in the groin is a pathological shunt between the groin artery and vein. In rare cases, the disorder is innate. More commonly, it is a consequence of blood vessel injury, for example, in a cardiac catheterization over the groin. It can cause swelling and pain in the groin. Since these are large blood vessels, another possible consequence of an AV fistula in the groin is a significant extra burden on the heart. This is because the blood through the fistula only has to overcome resistance and flow back directly to the heart.

AV fistula in the brain

An AV fistula in the brain is usually a carotid-sinus-cavernous fistula. This is an acquired morbid connection between the carotid artery and the blood-draining vessel, the cavernous sinus, in the skull. There are two different forms. The direct fistulas were the result of an injury with skull base fracture or due to tearing of a vascular graft of the artery (brain aneurysm). In this form, there is a high blood flow between the vessels.

An indirect fistula, however, usually arises spontaneously as a result of vascular disease or sinusitis. These are rather small connections of branches of the artery with the sinus, through which only small amounts of blood flow. Relevant, therefore, are above all the direct AV fistulas with high blood flow and flow reversal into the sinus system. The result may be a reduced blood flow to the cerebral vessels, which can lead to deficits such as blurred vision, dizziness or impaired consciousness

AV fistula in the spinal cord

An AV fistula in the spinal cord is a rare disease, but undetected and untreated in the worst case can lead to paraplegia. The cause is usually a acquired miscarriage between a small artery of the hard spinal cord and a vein of the spinal cord. The resulting increased pressure in the venous system can lead to slowly progressive damage to the spinal cord.

First symptoms may be paralysis, for which no other causes can be found (such as a herniated disc). The diagnosis is most likely to be made with magnetic resonance imaging, but is also often not sure. The treatment of AV fistula in the spinal cord can be done by occlusion using a vascular catheter. The earlier the disease is detected and treated, the better the prognosis.

AV fistula in the kidney

An AV fistula of the kidney is a direct morbid connection between the renal artery supplying blood and the blood-draining renal vein. In one of four cases, it is congenital, in the other cases, injury, inflammation, or surgery such as surgery. Frequently, the AV fistula does not cause any discomfort. In some cases, however, there is increased blood pressure, flank pain or bloody urine. For the diagnosis, in addition to an ultrasound examination, computer tomography of the abdomen as well as a representation of the vessels (angiography) are usually performed.

Usually, the AV fistula of the kidney is treated by the occlusion via a vascular catheter that has been advanced over the inguinal vessels. In some cases, surgery may require removal of part or even all of the kidney. Since the kidneys are among the most perfused organs, it can lead to life-threatening internal bleeding without treatment.

This is how AV fistulas are diagnosed

For the diagnosis of an AV fistula, an imaging examination of the blood vessels must be carried out. For these so-called angiographies, there are different methods such as DSA (Digital Subtraktiosangiography), in which X-rays are used to represent 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 may also be made by a special ultrasound examination. By the so-called Doppler effect, even the abnormal blood flow typical of an AV fistula can be measured and determined. Another simple way to detect a possible AV fistula is to listen to the stethoscope by the doctor. Superficial AV fistulas, such as in the groin, can be noticed by a characteristic flow noise. However, at least one of the mentioned imaging methods still has to be performed in order to be able to make a diagnosis.

Causes of AV fistula

There are three different origins of the causes of AV fistulas.

  1. On the one hand, it can be a congenital malformation, which may only become noticeable after many years or never causes any symptoms. It can then be detected, for example, as a random finding in an imaging examination. e
  2. A further form of AV fistula is the artificially produced compounds of an artery and vein for a dialysis treatment ("blood wash") in the case of severe renal dysfunction. This vascular connection is also usually called a dialysis shunt. This is created to ensure the necessary for dialysis high blood flow.

    These consequences are prevented during dialysis, in that a vascular surgical procedure specifically produces an arteriovenous fistula. This is usually done on the arm a connection between an artery and an adjacent vein. This causes an expansion of the vein and increased blood flow. The blood vessel can now easily be pierced with the needle during each dialysis treatment. Due to the faster blood flow it is not so fast to the formation of a blood clot.

    Nevertheless, the artificially produced AV fistula (usually referred to as a shunt) may close over time or be ignited by the repeated punctures. In such a case, if necessary, another artery and vein may be used to create a new AV fistula for dialysis.

    AV fistula after a cardiac catheter

    The emergence of an AV fistula after a cardiac catheter is a possible typical complication that occurs in about one in a hundred cases. In the procedure, the cardiac catheter is usually inserted through a puncture in one of the two groin arteries and advanced to the coronary vessels. Alternatively, the access path is via an artery on the arm. It can happen that the vascular wall is pierced by the introduced instrument and the adjoining, thin-walled vein is also injured. This results in a direct blood flow from the blood-bearing artery and the blood-draining vein bypassing the lower-lying body regions and smaller blood vessels.

    The resulting connection does not heal by itself because of the high pressure of the flowing blood, but it remains. In order to detect a possible AV fistula after a cardiac catheter at an early stage, the doctor will examine the inguinal region (or the arm) after the procedure. By scanning and listening with the stethoscope, the presence of an AV fistula can often already be detected. By means of an imaging examination, it can be decided whether the AV device must be repaired by another intervention.

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