As human and veterinary cardiology advances, more treatment options are becoming available for people and animals born with heart defects. Thankfully, the most common cardiac birth defect in dogs is now easily correctable with minimally invasive catheter-based surgery.
A patent ductus arteriosus, PDA for short, is a congenital (present at birth) defect that occurs when the ductus arteriosus fails to close at birth. The ductus arteriosus is a normal developmental blood vessel in all mammals that allows blood to bypass the nonfunctioning lungs during fetal development. In puppies, the ductus normally begins to close at birth with full occlusion (closing) at one week of age.
Failure of closure results in the patent (meaning “open” or “unobstructed”) ductus arteriosus. After birth, a PDA allows abnormal blood flow from the aorta back to the lungs. This over-circulation of blood causes undue stress on the lungs and left side of the heart.
Who Is at Risk?
PDA is the most common congenital defect in the dog and likely has a genetic basis. While the responsible gene has not yet been identified in dogs, breeds at greatest risk include the Chihuahua, Welsh Corgi, Collie, Maltese, Poodle, Pomeranian, English Springer Spaniel, Keeshond, Bichon Frise, Cavalier King Charles, German Shepherd, and Shetland Sheepdog. PDA occurs more commonly in female than male dogs and is relatively uncommon in cats.
Typically, a PDA is diagnosed in a puppy at one of the first routine veterinary visits. A characteristic “continuous” murmur heard loudest over the chest high in the left armpit is strongly suspicious for this defect. While most puppies are asymptomatic at the time of diagnosis, others will show poor weight gain and exercise intolerance. More advanced puppies may be in congestive heart failure (fluid in the lungs) at the time of diagnosis, with symptoms of increased respiratory rate, effort, and/or cough.
Once PDA is suspected, confirmation and treatment should be pursued with a board-certified veterinary cardiologist as soon as possible because early repair provides an excellent long-term prognosis for a completely normal life. Left untreated, approximately two-thirds of dogs with a PDA will die from congestive heart failure within their first year of life.
A presumptive diagnosis of PDA is confirmed with echocardiography (ultrasound of the heart). This noninvasive, non-painful tool can confirm the presence of a PDA, evaluate its current effect on the heart, and often characterize the size and shape of the ductus to best guide therapy. An echocardiogram is typically performed on awake puppies; extra-wiggly patients may require light sedation. Chest X-rays may be suggested to evaluate the lungs if respiratory symptoms are present and there is concern about congestive heart failure.
Treatment and Prognosis
Today, multiple treatment options are available for puppies with a PDA. Options include both minimally invasive catheter-based occlusion and open-chest surgical ligation.
In a catheter-based procedure, a long, thin, bendable catheter is inserted into a blood vessel in the neck or groin and gently threaded into the heart under the visual guidance of fluoroscopy (a real-time, moving X-ray image) – just as it is done in people. From this catheter, various devices can be deployed to occlude the PDA from the inside of the shunt.
Historically, catheter procedures were limited to depositing “coils” in the PDA. These spring-like loops of metal could block blood flow but had moderate potential for complications, such as coil movement or unsuccessful occlusion of blood flow.
Today, occluding devices made specifically for dogs are available and are quickly becoming the most common tools for transcatheter PDA closure. These devices are self-expanding, mesh-like structures made of nitinol (a metal alloy of nickel and titanium). They are available in a variety of sizes to fit snugly to the contour of the canine PDA. When open, the device physically obstructs the open ductus and promotes clot formation to definitively occlude blood flow and close the shunt. Success rates are greater than 95 percent with fewer complications than if using traditional coil techniques.
Catheter procedures are performed under general anesthesia but only require a small incision (often 3-4 cm) in the groin. Recovery time is very quick, and most puppies go home the next day with minimal restrictions. Given the success and limited invasiveness of catheter occlusion, open-chest surgical ligation is more often reserved for those patients whose size or specific PDA shape prevents a transcatheter approach.
Fortunately, either treatment provides an excellent long-term prognosis for a normal life.
Dr. Williams is a board-certified veterinary cardiologist who sees patients at both VCA San Francisco Veterinary Specialists (415-401-9200) and VCA Animal Care Center of Sonoma County in Rohnert Park (707-584-4343).