Arteriovenous Fistulae in Dogs

An arteriovenous Fistula is a condition where the connection between an artery and a vein is abnormally fragile. When a fistula is large not enough oxygen gets to tissue and in some cases, no oxygen at all is received. Because of the defect a dog’s heart tries to compensate by pumping blood at a much faster rate and this can lead to dog's experiencing congestive heart failure. An arteriovenous fistula is a serious condition and one that needs diagnosing and treating as soon as possible.

Where a fistula develops varies and they can form in various places around the body which includes the following:

• Head
• Neck
• Ear
• Tongue
• Limps
• Flanks
• Spinal cord
• Part of the brain called the cerebrum
• Lungs
• Liver
• The major artery that leads back to the heart
• Gastrointestinal tract

Breeds Most at Risk

The condition can affect any dog, but some breeds are more predisposed to developing arteriovenous fistulae than others, with the English Bulldogbeing high on the list.

The Symptoms to Watch Out For

Because an arteriovenous fistula can appear anywhere on a dog's body, symptoms tend to be quite different depending on their location. However, a lesion will form on the site of a fistula and these lesions are warm to the touch, but they do not cause a dog any discomfort or pain. With this said, if the lesion forms on a dog's leg, the signs of there being something wrong may well include the following:

• Swelling - when touched or pressed, an imprint is left on the affected skin which is known as a pitting oedema
• Ulceration
• Scabbing
• Lameness
• Gangrene - this is where the tissue has died and therefore turns the colour green

When the fistula affects a dog's heart it could lead to them suffering congestive heart failure, the symptoms of there being something wrong could include the following:

• Difficulty breathing - a condition known as dyspnea
• Coughing
• An increased heart rate which is known as tachypnea
• A reluctance to be exercised

When an arteriovenous fistula negatively impacts a dog’s internal organ, the symptoms could include the following:

• Abdominal distention - a dog's liver has been impacted
• Seizures - a dog's brain has been affected
• Weakness - a dog's spinal cord has been affected
• Paralysis - a dog's spinal cord has been affected

The Causes

It is very rare for a dog to be born with the condition because they generally form due to traumatic damage to blood vessels or because a tumour has developed at a certain site on a dog’s body. It could be due to a complication that occurred during or after surgery. A fistula can form if a dog has been given an injection close or around a blood vessel.

Diagnosing the Problem

A vet would need to have a dog's full medical history and be told how the onset of their symptoms occurred and they would then typically recommend doing the following tests:

• A full biochemistry profile
• A urinalysis
• A complete blood count
• An electrolyte panel - this helps a vet identify any complications often associated with the condition

Because an arteriovenous fistula can seriously impact blood flow, a vet might recommend taking thoracic X-rays which would establish if a dog's heart is larger than it should be. This could also permit them to see if there are any signs of a dog’s heart having to work overtime to compensate for the defect. A vet may also recommend doing a Doppler ultrasound which could show up abnormalities in blood flow in a lesion. When it comes to locating where an arteriovenous fistula has formed, a vet might recommend doing an echcardiogram and if they want to determine its outline, they may well suggest doing a selective angiograph.

Treatment Options

When a dog is diagnosed with the condition, the problem would need to be corrected which means undergoing surgery. The downside is that there is always a risk of a fistula recurring and in some instances a vet might recommend removing an affected appendage altogether to prevent this from happening. There is another less invasive procedure called “transcatheter embolisation” of blood vessels which allows vets to reach more remote lesions through a dog's blood vessels.

Living with a Dog with an Arteriovenous Fistula

When a dog is diagnosed and subsequently treated for an arteriovenous fistula, a vet would need to see them on a regular basis to evaluate their condition, more especially if they had to undergo any sort of surgery to correct the problem. Regular visits allows the vet to see if the problem has recurred in which case things can be caught and put right earlier rather than later.