Arteriovenous Fistula in Dogs
An arteriovenous fistula is an abnormal, low resistance connection between an artery and a vein. If large enough, the fistula may cause a significant fraction of the total cardiac output to bypass the capillary bed, making it so that the tissues receive little or no oxygen. The heart, in turn, tries to compensate for the lack of oxygen by pumping blood out to the body at a faster rate, which may lead “high output” congestive heart failure.
The location of arteriovenous fistulae varies; reported sites include the head, neck, ear, tongue, limbs, flank, spinal cord, cerebrum (part of the brain), lung, liver, vena cava (major vein leading back to the heart), and gastrointestinal tract.
Symptoms and Types
The symptoms associated with an arteriovenous fistula will ultimately depend on the size and location of the fistula. Typically, there is a warm, non-painful lesion at the site of the fistula. If the lesion is on a limb, the dog may display:
- Swelling where you can touch the limb and a fingertip impression is left in the skin (pitting edema)
- Lameness
- Ulceration
- Scabbing
- Gangrene (Tissue dies and turns green)
Signs of congestive heart failure, which is often associated with this type of fistula, include:
If the arteriovenous fistula causes organ failure, your dog may display:
- Distention of the abdomen (liver)
- Seizures (brain)
- Weakness or paralysis (spinal cord)
Causes
Dogs are rarely born with arteriovenous fistulas. Typically, they acquire the fistula due to traumatic damage to blood vessels, surgery complications, tumor(s), or problems arising from drawing blood or injections around the blood vessels (e.g., barbiturates)
Diagnosis
You will need to give a thorough history of your dog’s health, including the onset and nature of the symptoms, to the veterinarian. He or she will then perform a complete physical examination as well as a biochemistry profile, urinalysis, complete blood count, and electrolyte panel to help identify complications associated with an arteriovenous fistula. Biochemical abnormalities, for example, may suggest liver, kidney or other organ dysfunction.
Because arteriovenous fistulae significantly affect the dog's blood flow, thoracic X-rays may show enlargement of the heart and signs of over-circulation to the lungs. In addition, a Doppler ultrasound may show high-velocity, turbulent flow within the lesion.
To locate the arteriovenous fistula, your veterinarian may employ an echocardiogram on the dog. And to outline the lesion, which may be necessary for definitive diagnosis and is highly desirable for presurgical evaluation, the veterinarian may use selective angiography.
Treatment
Dogs with clinical signs must undergo surgery to divide and remove abnormal connections between blood vessels. However, surgery can be difficult and labor-intensive and may require blood transfusions. While often successful, the arteriovenous fistula may recur even after surgery. Some dogs may even require amputation of the affected appendage.
A newer treatment option called transcatheter embolization involves using a catheter to block blood vessels. This method is particularly advantageous because it is relatively noninvasive and provides access to remote lesions via the blood vessels.
Living and Management
Your veterinarian will want to schedule regular follow-up appointments to evaluate your dog, especially if it underwent surgery. This will also enable him or her to determine whether the arteriovenous fistula has recurred.