Patent ductus arteriosus, also known as PDA, is a congenital heart defect that can be found in any breed or species of animal including humans. When I graduated from veterinary school in 1960 we were taught about this condition but very few, if any, veterinarians were prepared to do thoracic surgery to attempt a correction.
While we were in school, Dr. Smith lectured to us about heart murmurs, including the continuous murmur associated with a PDA. I remember him standing at the lectern making a very particular noise, mimicking this murmur. The sound was “whoosh, whoosh, whoosh, whoosh.” I never heard the murmur in an animal when in school but the first time I did hear the murmur it sounded exactly like the noise Dr. Smith made in the lecture hall. The condition can also be detected by feeling the animal’s pulse.
When trying to explain this condition, I resort to a sketch where I draw a rough outline of the heart. I have the aorta coming off the left ventricle and supplying the body with arterialized blood, and the pulmonary artery coming off the right ventricle going to the lungs so carbon dioxide can be expelled from the blood and oxygen taken on. Before any mammal is born the lungs haven’t inflated yet, the fetus doesn’t need blood to go the lungs. There’s an opening between the pulmonary artery and the aorta so the blood can cross over into the aortam because until the lungs are inflated the pressure in the pulmonary artery is higher than the pressure in the aorta. The blood crosses over through a structure called the ductus arteriosus.
As soon as the newborn takes a couple of breaths, the alveoli — the little air sacs in the lungs — open and the blood vessels that surround each alveolus also open. The resistance to blood flow into the lungs is reduced and the blood pressure in the pulmonary artery drops below the blood pressure in the aorta. This causes the aortic side of the ductus to close since the ductus is more of a slit than a tube. So normally the ductus closes shortly after the animal starts breathing.
Unfortunately sometime, for reasons not yet completely understood, the ductus stays open. When that happens, it’s called a patent ductus arteriosus, or PDA. Since the pressure in the aorta is higher than the pressure in the pulmonary artery, the blood leaks continuously through the opening. With each heartbeat, the pressure increases in the aorta and that causes the leak to be greater.
When we listen to the heart of a normal animal it makes a noise that sounds like “lub dub . . . lub dub . . . lub dub.” A continuous murmur makes the whoosh, whoosh, whoosh sound as the pressure and blood flow into the pulmonary artery increase with each beat while the blood flows continuously surging with the beating heart.
The defect causes both the left and right sides of the heart to work harder and harder. The heart enlarges and finally it fails. Since my time in practice, veterinary medicine has made enormous advances. We now have board-certified veterinary surgeons capable of performing the relatively simple surgery to tie off the patent ductus.
We also have board-certified veterinary cardiologists who, if they make the diagnosis early enough, can use a catheter system to deliver a plug to the ductus and correct the problem without surgery. The key to a successful outcome is early diagnosis before the animal goes into heart failure, and that means a thorough physical examination by your veterinarian for your new pet while it is still young.
— By Dr. David Gross
Dr. David Gross of Edmonds graduated from Colorado State University’s veterinary school in 1960 and was in private practice for 10 years. He retired in 2006 as Professor and Head of Veterinary Biosciences, at the University of Illinois, Urbana-Champaign. Dr. Gross is the author of “Animals Don’t Blush,” which describes the unique patients and even more unique clients of a veterinary practice in Sidney, Montana in the early 1960s.