How AV fistulas are diagnosed
For the diagnosis of an AV fistula, an imaging examination of the blood vessels must be performed. There are various methods for these so-called angiographies, such as DSA (digital subtractive angiography), in which X-rays are used to visualise the vessels. An alternative is MR angiography (magnetic resonance), which does not require X-rays or other ionising radiation.
In both procedures a contrast medium must be introduced into the bloodstream. In addition, the diagnosis can also be made by a special ultrasound examination if necessary. The so-called Doppler effect even makes it possible to measure and determine the pathological blood flow typical of an AV fistula.
Another simple method of detecting a possible AV fistula is listening to the doctor with a stethoscope. Superficially located AV fistulas, such as those in the groin, can be noticed by a characteristic flow noise. However, at least one of the imaging procedures mentioned above must still be performed in order to make a diagnosis.
Causes of an AV fistula
There are three different types of AV fistulas. – Firstly, it can be a congenital malformation which may only become noticeable after many years or may never cause 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 connections of an artery and vein for dialysis treatment (blood washing) in cases of severe kidney dysfunction. This vascular connection is usually also called a dialysis shunt. This is created to ensure the high blood flow necessary for dialysis.
- The third type of AV fistula is the acquired form. This is usually the result of an injury or vascular disease. For example, an AV fistula in the brain can be the result of a skull-base fracture caused by a serious accident.
AV fistulas in the groin are in most cases the result of an injury caused by a medical intervention. For example, a cardiac catheter advanced through the inguinal artery can cause an injury to the vessel wall, which leads to the formation of an AV fistula. Dialysis (“blood washing”) is a renal replacement procedure that is used for severe kidney dysfunction.
At each treatment appointment, a vascular access has to be established through a puncture in a vein. This can easily lead to an inflammation of the blood vessel and clots can form. Ultimately, scarring can occur, which leads to a loss of vein function.
Dialysis prevents these consequences by specifically creating an arteriovenous fistula through vascular surgery. For this purpose, a connection between an artery and an adjacent vein is usually made on the arm. This causes the vein to dilate and the blood flow to increase.
The blood vessel can now be easily punctured with the needle during each dialysis treatment. Because of the faster blood flow, a blood clot does not form as quickly. Nevertheless, the artificially produced AV fistula (usually called a shunt) can become blocked over time or inflamed by the repeated punctures.
In such a case, another artery and vein may have to be used to create a new AV fistula for dialysis. The formation of an AV fistula after a cardiac catheterisation is a possible typical complication, occurring in about one in a hundred cases. During the procedure, the heart catheter is usually inserted through a puncture in one of the two inguinal arteries and advanced up to the coronary arteries.
Alternatively, the access route is via an artery in the arm. It is possible that the vessel wall is punctured by the inserted instrument and the adjacent thinner-walled vein is also injured. This results in a direct flow of blood from the blood-carrying artery and the blood-discharging vein, bypassing the lower body regions and smaller blood vessels.
Due to the high pressure of the blood flowing through the vein, the resulting connection does not heal on its own but remains intact. In order to detect a possible AV fistula after a heart catheter at an early stage, the doctor will examine the groin region (or arm) after the operation. The presence of an AV fistula can often already be detected by palpation and listening with the stethoscope. On the basis of an imaging examination it can be decided whether the AV fistula needs to be removed by a further operation.