After birth, blood flows from the right heart to through the pulmonary artery to the lungs. The blood returns to the left side of the heart from where it flows to the rest of the body through the aorta. Before birth, the lungs are not yet needed for breathing, so blood simply flows from the pulmonary artery through the ductus arteriosus to the aorta. At birth, due to pressure changes within the bloodstream, the ductus normally closes permanently, forcing blood to now enter the lungs where oxygen can be exchanged.
In the case of PDA (patent ductus arteriosus), the vessel fails to close completely, so some blood continues to bypass the lungs. When this happens, even though the puppy is breathing, the proper amount of blood is not flowing to the lungs, and therefore, the puppy is not receiving enough oxygen to meet tissue demands. PDA can exist in all breeds. Poodles, German Shepherds, Cocker Spaniels, Pomeranians, and Shetland Sheepdogs have the highest incidence. It is also more common in females than males.
What are the symptoms?
Initially, the puppy may show no symptoms. As it grows, however, the circulatory system cannot keep up with the tissues' need for oxygen. As the puppy grows and the oxygen demands are not met, the puppy may compensate for this by becoming less active. A puppy at rest requires less oxygen than one at play. Inactivity is one of the initial signs of PDA. In periods of excitement, these puppies may become short of breath and collapse. The gums will appear bluish (cyanotic), reflecting the oxygen shortage. As the blood flows through the abnormal ductus arteriosus, a murmur (caused by turbulent blood flow) can sometimes be heard without a stethoscope. This abnormal blood flow can occasionally be felt if the chest is palpated. Many affected puppies will not grow at a normal rate and will be smaller than their littermates. Depending on the severity of the condition, the signs may be noted anytime during the first year of life.
What are the risks?
Without treatment, almost all dogs with PDA will live a shorter than normal life. Depending on severity, some will live only a few weeks, others can survive longer.
What is the management?
Treatment of PDA requires surgery. The surgical procedure involves tying off the ductus arteriosus with suture material, thus routing all of the blood flow through the lungs. Surgery is quite successful and is best if done early before growth is affected.