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2016 Specialty



Patent Ductus Arteriosis in Dogs

Canine Congenital Heart Failure

What is Patent Ductus Arteriosus (PDA)?
A PDA is an abnormal persistent arterial connection between the aorta and the pulmonary artery after birth. At birth, mammals must adapt from living in a fluid environment (the amniotic fluid) and acquiring oxygen through the mother's blood, to breathing air and acquiring oxygen through their own lungs. The ductus arteriosus is very important in the adaptation process. This is a small communicating blood vessel between the pulmonary artery (which carries blood to the lungs), and the aorta (which carries blood to the rest of the body). Before birth, most of the blood from the fetal heart bypasses the fetal lungs via the ductus arteriosus. The lungs gradually become functional fairly late in fetal development.

  • Symptoms and Types—The degree to which your dog is affected depends on the magnitude of the defect. This can range anywhere from a small blind pocket off the aorta which doesn't cause any problems, to varying degrees of abnormal blood flow through the ductus between the aorta and the pulmonary artery. Most commonly there is a shunt from the left to the right side of the heart , with blood from the higher pressure aorta continuously shunted to the main pulmonary artery. This means an increased volume of blood to the lungs which results in fluid build-up (pulmonary edema) and volume overload to the left heart. You may see coughing, reduced tolerance of exercise, loss of weight, and eventually, congestive heart failure. Without surgery, premature death is likely.
  • Causes — Unfortunately, little is known about why PDA develops so frequently in domestic dogs. It may be influenced by a number of factors or combinations of factors, including environmental, infectious, nutritional, pharmaceutical and/or toxicological factors, among others. Usually, the exact causes of PDA are never determined. However, there are strong genetic factors which predispose certain dogs to retain a patent ductus arteriosus, especially in some smaller dog breeds. This is considered to be an inherited disorder by most veterinary cardiologists. At birth, the blood supply from the mother is of course cut off, the dog (or other mammal) begins breathing on its own, and blood flow through the ductus arteriosus decreases dramatically. Within a few days, the ductus closes off completely. Where the ductus does not close, the dog is left with a patent ductus arteriosus (PDA). The extent to which this affects the dog depends on the degree of patency, or opening, of the ductus.
    Less commonly, there is a right-to-left shunt. This may be the case from birth or, it may develop because the PDA is so large that the pressure in the lungs, and resultant resistance to this pressure, markedly increase. In effect, the circulation is the same as when the dog was a fetus - that is, some of the blood leaving the right side of the heart bypasses the lungs entirely. This results in circulation of poorly oxygenated blood. Your dog may have shortness of breath and weakness or collapse in the hind limbs.
  • Diagnosis—PDA is the most commonly diagnosed congenital heart defect in dogs. It occurs in many breeds and is seen more often in females. Usually a PDA is first suspected when the veterinarian hears the characteristic continuous "machinery" heart murmur when your dog is examined at the time of vaccination. There are radiographic and electrocardiographic signs to confirm the diagnosis. At this point your puppy will not likely show any clinical signs relating to the PDA.
    It is important to remember that the presence of a heart murmur in a puppy does not necessarily mean that the puppy has heart defects or disease. Many puppies have a low-grade heart murmur early in life that disappears by about 6 months of age. These puppy murmurs are completely normal.
  • Treatment—Patent ductus arteriosus (“PDA”) is one of the congenital canine conditions that is highly treatable – in fact, surgically correctible – in most affected dogs. The therapeutic goal is to occlude or tie off the shunt defect and thereby restore normal blood flow between the right and left heart chambers. This treatment it is extremely effective in young animals that have not yet deteriorated to the point of congestive heart failure.
    The current preferred surgical technique is called a ductus ligation, which basically involves entering the thoracic (chest) cavity and tying off (ligating) the abnormal vessel. This procedure is not especially long or complicated, but of course any surgery involving general anesthesia carries with it certain risks. If a dog has progressed to congestive heart failure before surgery, diuretics and vasodilators may be prescribed pre-operatively, together with enforced cage rest, to help manage the condition and increase the dog’s chances of successful surgery. Diuretics help to reduce the fluid retention that commonly accompanies congestive heart failure, and vasodilators can relieve the effects of high blood pressure.
  • Prevention—No known prevention at this tme.

    *NOTE: The outlook for most dogs after PDA repair surgery is very good to excellent. Once the shunt is closed off and blood flow returns to normal, the heart and heart vessels seem to bounce back to good function and health. Indeed, many dogs are able to enjoy physical activities that they could not before the surgery. Heart surgery understandably is intimidating, but, it really is the best option for dogs with a patent ductus arteriosus. Most animals have a normal lifespan following surgical treatment. Without treatment, the prognosis is grave. Untreated PDA almost always leads to congestive heart failure and, ultimately, to death .

Other health problems can occur in your Maltese. If you notice anything unusual with your dog, take it to the vet immediately. This webpage is for general information only and is not intended to be a medical guide.

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