Abnormal Passage Between Artery and Vein in Dogs

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:

• Coughing
• Difficulty breathing (dyspnea)
• Increased heart rate (tachypnea)
• Exercise intolerance

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.