Patent Ductus Arteriosus (PDA) in Dogs

Overview of Patent Ductus Arteriosus (PDA) in Dogs

The ductus arteriosus is a blood vessel that connects the two main arteries of the body – the aorta and the pulmonary artery. This blood vessel is normal in the fetus, but shortly after birth, it should close. When the ductus arteriosus remains open or patent after birth, this abnormal communication between the aorta and pulmonary artery passes extra volumes of blood into the lungs.

Patent ductus arteriosis (PDA) is a birth defect representing the second most common congenital heart defect of dogs. Approximately seven out of 1000 live birth puppies are affected.

Generally, there are no serious symptoms of PDA unless congestive heart failure has caused fluid buildup in the lungs. The condition is typically identified in puppies during a routine veterinary visit for vaccinations. Continual blood flow through the PDA into the lungs produces a continuous (machinery) heart murmur.

Even when the veterinarian identifies a PDA, most people believe their dog is normal. In some cases, the dog can be smaller than littermates or play less vigorously. However, the situation can be very misleading as symptoms usually occur within a year of diagnosis. If untreated, about 60 percent of affected dogs die within a year of diagnosis.

When caught early, and following treatment with successful closure of the PDA, most dogs live a normal life. Unless there are complications from other heart defects or heart failure has already developed, there is rarely any future need for medication. While special circumstances can influence the prognosis, most cases are straightforward.

PDA is genetically determined in almost every case, and this fact impacts the value of purebred dogs used for breeding. PDA is common in the miniature poodle, collie, Maltese, Shetland sheepdog, German shepherd dog, cocker spaniel, Pomeranian, and Labrador retriever. Female dogs are predisposed.

What to Watch For

• Breathing difficulties
• Coughing
• Exercise intolerance
• Lethargy

Diagnosis of Canine Patent Ductus Arteriosus

Various diagnostic tests are needed to recognize PDA, and exclude other diseases. Some of the necessary tests may include:

• Complete medical history and physical examination including auscultation (stethoscope examination) of the heart and lungs. The heart murmur of PDA is characteristic and most experienced veterinarians learn to make the diagnosis simply by listening. Since other birth defects can also cause heart murmurs, a veterinary cardiologist may be consulted if the diagnosis is in doubt.
• A chest X-ray (radiograph) can help determine the severity of the problem.
• An electrocardiogram (EKG) can assist with the diagnosis.
• An echocardiogram with Doppler (cardiac ultrasound) is the definitive diagnostic test. This may require referral.
• Routine blood tests may be performed prior to any anesthesia.

Treatment of Canine Patent Ductus Arteriosus (PDA)

• The conventional treatment is an operation done shortly after diagnosis. The PDA is closed with surgical suture.
• Aspirin, indomethacin and other prostaglandin inhibitors do NOT work in dogs and should not be given to close the ductus – these are dangerous drugs in young pets.
• Surgery should not be delayed by waiting for symptoms to develop.
• Medical treatment may be necessary before surgery if symptoms (coughing, difficult breathing) are present.
• In some referral centers, the PDA may be closed using special catheterization techniques.

Home Care and Prevention

Before any surgery, provide only the exercise your dog can tolerate. Do not allow your dog to become short of breath with activity.

Follow up with your veterinarian after surgery or surgical closure. In most cases, only a suture removal is needed and further follow-up is unnecessary.

There is no way to prevent PDA but dogs diagnosed should not be bred, even if the defect has been corrected.

In-depth Information on Patent Ductus Arteriosus (PDA) in Dogs

Patent ductus arteriosus (PDA) is a common birth defect. The pressure in the aorta is higher than the pressure in the pulmonary artery, therefore, blood crosses the ductus from left (aorta) to right (pulmonary artery). Very infrequently, the increased blood flowing into the lungs injures the pulmonary blood vessels. This can reverse the path of blood flow from right to left. In this case, unoxygenated blood flows into the aorta to the rear limbs, causing weakness and complications such as an elevated red blood cell count (polycythemia), which makes the blood thick. Symptoms are usually precipitated by exercise and include weakness and even seizures.

There are a number of reasons for heart murmurs in puppies. These conditions require different management and include:

• Anemia and fever can lead to soft to moderate intensity murmurs.
• Ventricular septal defect, a “hole in the heart” between the two ventricles, is common.
• Aortic stenosis (or subaortic stenosis) is the most common heart defect in dogs today. This is a narrowing of the outlet from the left ventricle and obstructs blood flowing into the aorta.
• Pulmonic stenosis is similar to aortic stenosis but affects the other side of the heart.
• Innocent murmurs (not pathologic) are common in growing puppies. These sound different from PDA to the experienced examiner. Furthermore, these murmurs become softer and most always go away by the time of the rabies vaccine, which is usually given between four and 6 months of age.

There are also many causes of stunted growth and of shortness of breath. Your veterinarian should investigate these symptoms.

Veterinary care should include diagnostic tests and subsequent treatment recommendations.

Diagnosis In-depth of Patent Ductus Arteriosus (PDA) in Dogs

Diagnostic tests are needed to recognize PDA and exclude other diseases. A definitive diagnosis may require additional tests including chest X-rays, electrocardiogram and ultrasound examination of the heart (echocardiography or cardiac echo). It is important to exclude other congenital heart defects. Tests may include:

• Examining the heart with a stethoscope and detecting a characteristic heart murmur
• Chest X-rays (thoracic radiographs) can demonstrate the heart size and characteristic changes found in PDA. Heart failure can be diagnosed from this examination.
• EKG is a supportive diagnostic test. It is less valuable than an echocardiogram, but is useful when an echo is not available.
• Echocardiogram is an ultrasound test that can image the heart. Though difficult to see, experienced examiners can visualize the PDA. Furthermore, other heart birth defects can be excluded. Doppler studies are blood flow studies capable of definitely diagnosing the abnormal flow across the ductus. This is a referral examination done by a specialist in most cases.
• Angiography (dye studies) is almost never done today.
• Biochemistry may be tested with serum blood tests to determine general health and check for secondary conditions.
• Routine blood tests may be performed prior to any anesthesia. In the rare case of right to left PDA, the complete blood count (CBC) may show an elevated packed cell volume (PCV).

Treatment In-depth of Patent Ductus Arteriosus (PDA) in Dogs

Treatments for PDA may include one or more of the following:

• The conventional treatment is surgery done shortly after diagnosis. This involves general anesthesia and an incision in the chest (thoracic surgery). The PDA is isolated and closed with surgical suture. There is no benefit to delaying surgery. In fact, the chances of a dog developing heart failure or suffering irreversible damage to the heart muscle only increase with time. Operative success should be greater than 90 percent, even in the smallest dogs. Activity should be restricted until surgery is completed.
• Medical treatment (furosemide, +/- digoxin) may be necessary before surgery if symptoms such as coughing or difficult breathing are present. These symptoms are typically caused by left-sided heart failure – the accumulation of fluid, or pulmonary edema, in the lungs.
• Aspirin, indomethacin and other prostaglandin inhibitors sometimes used to close the PDA in premature human babies do NOT work in dogs and should not be given to close the ductus. The canine ductus lacks the smooth muscle capable of responding to these drug therapies. Furthermore, these are dangerous drugs in young pets, capable of causing kidney injury and stomach bleeding.
• In some referral centers, the PDA may be closed using special catheterization techniques. Some of these procedures can be done without any incision at all (percutaneous PDA closure), but the techniques require special experience and equipment and are not widely available.
• When surgery is not an option, and heart failure has occurred, drug therapy with furosemide, enalapril or benazepril and digoxin is often prescribed. A salt-restricted diet is enforced.
• Dogs with polycythemia caused by right to left shunting PDA should be treated periodically by phlebotomy, which is removing blood to control the red blood count and viscosity of the blood. Surgery cannot be done in these pets.

Follow-up Care of Dogs with Patent Ductus Arteriosus (PDA)

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical. Administer prescribed medications as directed and be certain to contact your veterinarian if you are experiencing problems treating your dog.

Following successful PDA closure, the initial follow up is about 10 to 14 days later. In uncomplicated cases, no further follow-up is required. Referral to a veterinary cardiologist can be helpful in hard to diagnose cases or when there are questions about alternative treatment options.

If heart failure has occurred, follow-up care is critical.