Arteriovenous Fistula in Dogs
In dogs, an arteriovenous fistula refers to an abnormal connection of low resistance between an artery and a vein. When sizable, this connection can divert a significant portion of the total cardiac output away from the capillary bed, resulting in insufficient oxygen delivery to tissues. Consequently, the heart compensates for the oxygen deficiency by increasing the rate of blood pumping to the body, potentially leading to “high output” congestive heart failure.
Arteriovenous fistulae can occur at various locations in dogs, including 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 linked with an arteriovenous fistula in dogs will vary based on the size and location of the fistula. Typically, a warm, non-painful lesion manifests at the fistula site. If the lesion occurs on a limb, observable symptoms may include:
- Swelling where pressing on the limb leaves a fingertip impression in the skin (pitting edema)
- Lameness
- Ulceration
- Scabbing
Gangrene (Tissue death resulting in green discoloration)
- Signs of congestive heart failure, often associated with this type of fistula, comprise:
- Coughing
- Difficulty breathing (dyspnea)
- Increased heart rate (tachypnea)
Exercise intolerance
- If the arteriovenous fistula leads to organ failure, your dog may exhibit:
- Abdominal distention (liver)
- Seizures (brain)
- Weakness or paralysis (spinal cord)
Causes
Arteriovenous fistulas are seldom congenital in dogs. Usually, dogs develop these fistulas as a result of traumatic injury to blood vessels, complications from surgery, tumors, or issues arising from blood draws or injections around blood vessels (e.g., barbiturates).
Diagnosis
When visiting the veterinarian, it’s essential to provide a detailed history of your dog’s health, including the onset and characteristics of symptoms. The veterinarian will conduct a thorough physical examination and may request a series of diagnostic tests, such as a biochemistry profile, urinalysis, complete blood count, and electrolyte panel, to detect any complications associated with an arteriovenous fistula. Biochemical abnormalities can indicate dysfunction in organs like the liver, kidneys, or others.
Since arteriovenous fistulas significantly alter blood flow in dogs, thoracic X-rays may reveal heart enlargement and signs of excessive blood circulation in the lungs. Additionally, a Doppler ultrasound may exhibit high-velocity, turbulent flow within the lesion.
To pinpoint the location of the arteriovenous fistula, your veterinarian may utilize an echocardiogram. Selective angiography may also be employed to delineate the lesion, which is crucial for a definitive diagnosis and highly beneficial for presurgical assessment.
Treatment
Dogs showing clinical symptoms typically necessitate surgery to separate and eliminate abnormal connections between blood vessels. However, surgery can be challenging and demanding, potentially requiring blood transfusions. Although often effective, arteriovenous fistulas may reoccur even after surgical intervention. In some cases, dogs may require amputation of the affected limb.
A more recent treatment option, known as transcatheter embolization, utilizes a catheter to block blood vessels. This method offers several advantages, as it is relatively noninvasive and allows access to remote lesions through the blood vessels.
Living and Management
Your veterinarian will recommend scheduling regular follow-up appointments to assess your dog’s condition, particularly if it has undergone surgery. These appointments will also allow the veterinarian to monitor for any recurrence of the arteriovenous fistula.