The aorta is the main artery that feeds oxygenated blood from the left side of the heart to the body. The pulmonary (lung) artery travels from the right side of the heart to the lungs, carrying deoxygenated blood to be oxygenated. Once the blood has been oxygenated by the lungs, it then returns to the left side of the hearty through the pulmonary veins to be pumped out into the body by the aorta.
In the womb, the fetus’ descending aorta is connected to the pulmonary artery by the ductus arteriosus blood vessel, allowing blood to flow directly from the right side of the heart to the aorta, without stopping for oxygen in the lungs. This is because the fetus gets its oxygen from the mother’s bloodstream and does not yet need to have its own blood oxygenated.
Normally at birth, this connection is no longer patent (open). Once a newborn has begun to breath on its own, the pulmonary artery opens to allow blood to flow from the right side heart into the lungs to be oxygenated, and the ductus arteriosus closes. But in patent ductus arteriosis (PDA) the connection remains patent. Consequently, blood is shunted (diverted) in abnormal patterns in the heart. PDA allows blood to flow from the aorta into the pulmonary artery, and then to the lungs.
If the shunt is moderate to large, it can cause left-sided congestive heart failure from blood volume overload on the left side of the heart. Less frequently, a large-diameter PDA will cause injury to the blood vessels in the lungs, from the excess amount of blood flowing into he lungs. High blood pressure in the lungs, and reversal of the shunt so that the blood goes from right to left (pulmonary artery to the aorta), as well as the typical PDA shunt direction of left to right (aorta to pulmonary artery) can be expected.
This atypical right to left shunting of a PDA can cause the aorta to carry blood that is low in oxygen, sending a signal to the body to produce more red blood cells (since they carry oxygen), making the blood too thick.
PDA can affect both dogs and cats.
Look out for respiratory (breathing) distress, coughing, exercise intolerance and increased breathing rates, hind legs may be weak during exercise, arrhythmias (an irregular heart beat), a blood clot from the right to left, pink or bluish gums, bluish skin around the anus or vulva, left-sided congestive heart failure, a rapid and irregular heart beat and stunted growth.
PDA is a genetic predisposition, a birth defect, and for owners, there is no way to prevent it. Breeders should not be breeding dogs with PDA.
To diagnose PDA, your veterinarian will need to perform a thorough physical examination, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. Your dog’s level of oxygen in his blood may also be tested (expect blood samples to be taken from different locations for comparison). Your vet may also need to use radiograph or ultrasound imaging to look at your dog’s heart. Oftentimes, an X-ray can show left heart enlargement, but a heart with PDA will appear as normal size on an X-ray.
Your vet may prescribe oxygen therapy, nitrates and cage rest. When he has regained stability, he will need surgery as soon as possible. The operation may be performed on puppies as young as seven to eight weeks of age. Unfortunately, if your dog has right to left shunting, he will not be eligible for surgery. After surgery and two weeks recovery time, your dog should be perfectly fine and you will all soon forget he was ever sick.