Patent Ductus ArteriosusPatent ductus arteriosus (more commonly shortened to PDA) is considered to be the most common congenital heart defect in dogs. Remember, congenital means present at birth and is not necessarily synonymous with hereditary.
The ductus arteriosus is a normal blood vessel in the developing fetus that shunts blood from the pulmonary artery on the right side of the heart directly to the aorta, detouring around the left heart and the lungs that are not working in the uterus (no air to breath yet). Generally this duct closes in the first few days after birth. If it does not, or if it only closes on one side (a ductus diverticulum), then blood can be pushed through the duct, causing a distortion in the flow of blood which will result in a murmur that can be heard with a stethoscope. Most often it is described as a 'washing machine' like murmur since the blood 'swishes' from its normal course, much like the increasing sound when water in a creek enters rocky rapids. These puppies may have a 'bounding' femoral pulse or you might be able to feel a 'thrill' over the area of the chest where the heart lies on the left.
Most of the time the shunt is from the left side (oxygenated blood in the aorta) to the right side, causing back flow into the lungs and left side of the heart.
Generally the murmur is detected during a routine puppy check up. Signs can include puppies that fail to thrive or grow on as well as their siblings. One very young puppy I had years ago (the only PDA I've ever had in Cardigans) was crying continuously and very distressed. The murmur was so bad in this puppy the cardiologist and I were convinced it was either an atrial septal or a ventricular septal defect. On necropsy, it turned out to be a PDA. We were both surprised at the puppy's actions because rarely does a PDA puppy appear this sick until well advanced with heart and lung disease.
Most commonly surgery is performed to correct PDA and should be done before any lasting damage occurs to the heart and lungs (generally before 5 months of age). There are some more recent non-surgical techniques being used to close PDAs. Early correction of a PDA usually leads to a normal life in a dog ; fortunately dogs do not often have more congenital heart defects with a PDA (unlike cats). Left untreated, PDAs will usually develop left side heart failure and eventually die.
Dogs with a right-to-left shunt usually develop pulmonary hypertension. Once this occurs, surgical correction is of little use because duct closure may lead to right sided heart failure. These puppies are usually lethargic and may have weakness of the rear limbs as well as an increased red blood cell count and cyanosis (due to poor oxygenation of the blood). These also do not usually have the washing machine murmur but a different type of murmur more difficult to detect.
Breeds where it appears more commonly (depending upon the textbook consulted) include Miniature Poodles (where breeding trials have demonstrated it as an inherited disease and it is believed to be polygenetic), Pomeranians, Collies, Shelties, Maltese, English Springer Spaniels and Welsh Corgis (Pembroke or Cardigan rarely specified). The only published case report (as opposed to personal communication) I'm personally aware of in corgis is in Pembrokes, where a related family had an increased tendency to develop PDA with pulmonary hypertension (see abstract below), so the reference of Lauren's would probably list Pembrokes if they wanted to be breed specific.
Kathleen M. Harper
29 October 2003
Patent ductus arteriosus and pulmonary hypertension in related Pembroke Welsh corgis
J Am Vet Med Assoc (Journal of the American Veterinary Medical Association.) 1993 Mar 1; 202(5): 761-4
Abstract: Patent ductus arteriosus (PDA) and pulmonary hypertension were diagnosed in 5 related 12- to 24-week-old Pembroke Welsh Corgi dogs. A ductus diverticulum and small PDA were diagnosed in the pups' sire. Multiple factors likely contribute to the early development of pulmonary hypertension, including pulmonary hyperperfusion, genetic predisposition, and atmospheric pressure. The dogs of this report had a strong genetic predisposition to PDA, had large-diameter PDA associated with pulmonary hyperperfusion, and lived at altitudes of 5,000 to 7,000 feet above sea level. This combination of factors likely had an additive influence on the pulmonary vasculature, resulting in accelerated development of pulmonary hypertension in these dogs. Early recognition and treatment of PDA is critical in this setting before the development of severe pulmonary hypertension and uncorrectable disease.