An arteriovenous fistula is an abnormal connection between an artery and a vein. The fistula may cause a portion of the cardiac output to bypass the capillary bed, so that the tissues receive little or no oxygen. To compensate for the lack of oxygen, the heart tries to pump blood at a faster rate, which may lead to “high output” congestive heart failure.
The location of arteriovenous fistulae could be anywhere including head, neck, ear, tongue, limbs, flank, spinal cord, cerebrum, lung, liver, vena cava, and gastrointestinal tract.
The symptoms associated with an arteriovenous fistula will 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 (pitting edema)
Signs of congestive heart failure, which is often associated with this type of fistula, include:
Difficulty breathing (dyspnea)
Increased heart rate (tachypnea)
If the arteriovenous fistula causes organ failure, the dog may display:
Distention of the abdomen (liver)
Weakness or paralysis (spinal cord)