Arteriovenous fistula is a rare condition. It involves the formation of a direct channel between an artery and a vein through which blood flows and therefore bypasses the capillary bed. The blood doesn’t reach its intended destination and is “short-circuited” away down the vein.
Let’s look at the blood supply to a paw:
- Blood flows toward the paw in an artery, which eventually forms arterioles (tiny arteries) in the paw tissue leading into the capillary bed, a lace-like web of tiny vessels through which oxygen is supplied to the tissue and carbon dioxide removed.
- The “dirty” blood is removed from the capillaries via veinules and then veins to circulate back to the heart for re-oxygenation.
- When a fistula forms, this system is short-circuited. The blood doesn’t make it as far as the paw, but travels from artery to fistula to vein. Thus the tissue of the paw doesn’t get the blood flow it needs to remain healthy.
The signs that a pet has an arteriovenous fistula depend on the location.
If we take the paw example, in the early stages the paw may swell (develop edema). The lack of proper blood supply means metabolic toxins build up in the paw, damaging the tissue and causing ulcers to develop and become infected.
Ultimately, the lack of blood supply can result in serious conditions such as gangrene.
However, an arteriovenous fistula is not always serious. There are multiple arteries supplying any particular region, and if one stops working, then another (or collateral) artery may take over its work. In these cases, you may either not be aware of the fistula or, if it is near the surface of the skin, notice a distended, pulsating blood vessel.
Unfortunately, some cases can be life-threatening, such as if a fistula develops in the lungs. In this case, blood bypasses the lung and the patient may have difficulty breathing, have a blue tinge to their mucus membranes or even have a stroke.
Don’t Miss: 5 Symptoms of a Stroke in a Dog or Cat
Some animals are born with an arteriovenous fistula, but more commonly it results from trauma.
In the case of trauma, scar tissue forms, impeding the regular blood flow, and the circulation adapts and forms new vessels, but not necessarily to the long-term benefit of the patient.
Diagnosis usually involves specialist imaging. Until the availability of MRI scanners, the most common method was using contrast agents to see where they went.
This involves anesthetizing the patient and injecting a liquid contrast agent into the artery supplying the fistula that shows up on radiography. A series of special radiographs map out the flow of the contrast to see if the pattern is normal or involves extra vessels.
MRI scans have largely superseded this method, and provide a highly detailed 3-D map of the vessels to a particular area.
Don’t Miss: What to Do If Your Dog or Cat Has a Heart Murmur
Correction of this problem is a specialist procedure. Traditional methods of treatment include identifying and ligating the nutrient artery to the fistula.
However, newer and more sophisticated techniques are emerging that require placing a special catheter into the fistula and inflating a balloon cuff around it so it is blocked. The aim is to plug the fistula so that the blood supply resumes along its proper route.
It is difficult, if not impossible, to prevent an arteriovenous fistula from forming other than to be a responsible pet caregiver and take steps to ensure your pet is not exposed to unnecessary risks of accident or trauma.
- “Acquired peripheral arteriovenous fistula in a dog.” Butterfieled, Hix, Pickrel & Johnson. J Am Vet Med Asso. 1980 Mar 1: 176(5): 445–448.
- “Circulatory changes in the dog produced by acute arteriovenous fistula.” Van Loo & Heringman. Am Jour Physiology. 1 July 1949: 158, No. 103–112.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 1, 2015.