Introduction
Abnormal connections between the left and right chambers of the heart are called “intracardiac shunts.” The most common of these in dogs is patent ductus arteriosus (“PDA”), which shunts blood between the pulmonary trunk arteries and the descending aorta. During prenatal life, this channel allows most fetal blood to bypass the nonfunctional lungs. This shunt is normal in fetuses, but should close within 24 hours of birth once the lungs are inflated. When the ductus arteriosus remains open -or “patent” - it puts increased burdens on the heart’s left chambers, causing them to dilate and causes reduced blood flow through the aorta. Left untreated, a PDA can contribute to congestive heart failure in dogs. PDAs occur in all breeds and ages of dogs, but most commonly are identified in young animals.
Causes of PDA in Dogs
Arterial shunts are normal in fetal animals (including people), but they should close within a short time of birth. PDAs are one of the most common congenital heart defects in dogs, but little is known about why this condition develops so frequently in dogs. Congenital defects are those which are present at birth. They can be caused for many reasons or combinations of reasons, such as environmental, infectious, nutritional, pharmaceutical, toxicological and others. Often the exact causes are unknown. However, there do appear to be genetic factors which predispose the ductus arteriosus to remain patent in certain animals, especially in some smaller dog breeds, including Maltese, Pomeranians, Yorkshire terriers, Shetland sheepdogs and toy and miniature poodles.
Signs of Patent Ductus Arteriosus
Clinical sign of PDA may take years to develop, but some dogs show mild signs early as one year of age. These signs can include exercise intolerance, coughing, lethargy, fatigue, seizures and other episodes of fainting or collapse. It is critical to detect PDA as early in a dog’s life as possible, because this congenital defect is almost always surgically correctable. Surgery has a much better chance of success if the PDA is detected before the onset of congestive heart failure or other irreversible heart damage. Also, reputable breeders will want to take affected animals out of their breeding programs.
Diagnosis and Treatment of Patent Ductus Arteriosus in Dogs
Patent ductus arteriosus is usually diagnosed during a routine physical examination of a young dog visiting the veterinarian for vaccinations and showing no overtly abnormal clinical signs. PDA shunts cause a continuous heart murmur that is louder and then softer at identifiable phases of the heart cycle, which a veterinarian can detect when listening to the heart through a stethoscope.
Dogs with PDAs also can have bounding pulses. Normally, a veterinarian will want to take radiographs (X-rays) of the chest, conduct an electrocardiogram (ECG) and possibly perform an ultrasound examination as well. Advanced tests can be done to confirm a diagnosis of PDA; these usually are performed by a specialized veterinary cardiologist. Once a PDA is diagnosed, the standard treatment in almost all cases is surgery to stop the flow of blood through the shunt. If an animal already has developed congestive heart failure, steps can be taken to help manage the condition before surgery is performed, including the use of diuretics, vasodilators and cage rest.
It is important to remember that the presence of a heart murmur in a puppy is not necessarily reflective of heart defects or disease. Many puppies have a low-great” heart murmur early in life, which disappears by about 6 months of age. These murmurs are normal.
Outlook for Dogs with Patent Ductus Arteriosus
The outlook for dogs with PDA is very good after surgical correction of the defect. Most animals have a normal lifespan following treatment.