The developing fetus within the womb does not use its own lungs to mix blood and oxygen. Instead, it receives oxygen-rich blood from its mother through placental circulation. A blood vessel (the ductus arteriosus) in the unborn fetus bypasses the lungs to send blood to the rest of the body. Only a small amount of fetal blood flows through the lungs.
Normally, the ductus arteriosus closes within a few hours of birth. In some animals, the ductus does not close, and blood continues to bypass the lungs and not pick up oxygen. A human infant with patent ductus arteriosus is called a “blue baby.”
This defect occurs more in Poodles, Collies, Pomeranians, and Shetland Sheepdogs than in other breeds. Many affected pups die of heart failure within the first few weeks of life, but most affected pets that live to 8 weeks of age survive into adulthood. When the bypass is small, the dog may live a normal life without ever showing any ill effects. Patent ductus arteriosus also occurs in cats.
Important Points in Treatment
1. Surgical closure is the only means of correcting patent ductus arteriosus. Medical therapy helps stabilize animals in heart failure only for short periods.