Patent Ductus Arteriosus (PDA) in Dogs & Cats

Understanding Your Pet's Heart Condition

A patent ductus arteriosus (PDA) is a congenital cardiac anomaly, or a structural abnormality in the heart that is present at birth, rather than developing later in life. Specifically, a PDA is characterized by the persistent functioning (or patency) of a certain blood vessel called the ductus arteriosus that normally spontaneously closes and stops carrying blood within a few hours to several days after birth. To understand the significance of a PDA, a brief explanation of blood circulation through the body is helpful.

The heart is divided by a septum down the middle into a right side and a left side, with two chambers (an atrium followed by a ventricle) on each side. The right side of the heart is dedicated to pumping blood to the lungs via the pulmonary artery. The left side of the heart is responsible for pumping blood to the rest of the body's organs via the aorta. Normally, there is no direct connection between any of the right- and left-sided structures once an animal is born and begins breathing air.

Why This Blood Vessel Matters

In the unborn fetus, the ductus arteriosus is critical to normal blood flow, allowing blood to be diverted away from the lungs (which are not yet being used) by connecting the pulmonary artery to the aorta. After birth, however, due to a pressure drop that occurs in the lungs as the neonate begins to breathe, a PDA carries blood in the opposite direction and allows excessive return of blood to the chambers on the left side of the heart. Eventually, the overload placed on these chambers leads to the development of congestive heart failure in many dogs and cats with a PDA.

How Will My Veterinarian Diagnose PDA?

A congenital heart condition is often first suspected following detection of a heart murmur during routine physical examination in a young dog. This is an abnormal "whooshing" noise associated with the normally crisp heart sounds, heard while listening to the heart with a stethoscope. Although many different conditions result in the presence of a heart murmur, the murmur associated with a PDA typically has a distinctive sound often described as continuous or resembling a washing machine.

If congestive heart failure is already present at the time of first examination, other findings may include abnormally loud lung sounds (also heard with a stethoscope) as well as rapid or labored breathing.

Tests Your Pet May Need

Diagnosis of a PDA is confirmed by performing an echocardiogram. This is an ultrasound examination of the heart, during which information is collected about the size and function of the heart, as well as blood flow through its chambers. In the case of a PDA, observation of turbulent blood flow through the ductus arteriosus leads to this specific diagnosis. Assessment of the shape of the PDA is also made, since this has implications regarding therapy.

Chest x-rays are used to obtain a "big picture" view of the heart within the chest cavity. They allow evaluation of the lungs and are necessary to rule out congestive heart failure. An electrocardiogram is performed in order to identify and characterize arrhythmias that may be present, and to guide antiarrhythmic therapy if necessary. Bloodwork is performed prior to general anesthesia for PDA correction or if cardiac medications are begun or changed.

Treatment Options for Your Pet

Currently, two options exist for correction of PDAs in dogs and cats, both aimed at terminating blood flow through the ductus arteriosus. Each procedure has pros and cons which are discussed in detail prior to deciding which way to proceed.

Surgical Ligation

The more traditional and invasive approach involves surgical ligation of the PDA. In this procedure, the PDA is isolated within the chest cavity and a surgical knot is tied around it, thereby occluding blood flow through it.

Transvascular Occlusion

The newer and less invasive approach is called transvascular occlusion. This is a catheter based procedure where a device called an Amplatz Canine Ductal Occluder (ACDO) is placed within the PDA. Here, the ACDO, which is made of a fine wire mesh, is advanced into a small artery in the leg, and then through progressively larger arteries to reach the ductus arteriosus. The ACDO is delivered directly into the PDA where it blocks blood flow from within the vessel.

The success of transvascular occlusion depends on the PDA having the shape of a cone or funnel, as opposed to a simple tubular shape which will not retain the deposited ACDO device. Preliminary determination of the shape of the PDA is made during the initial echocardiogram. If a conical or funnel-shaped PDA is suspected and coil occlusion is chosen, a special "contrast" x-ray study (angiogram) is used to confirm the shape and size of the PDA just prior to delivery of the device.

Transvascular occlusion with the ACDO device is preferred over surgical ligation due to its minimally invasive nature, higher success rate, and lower incidence of complications. However, in some cases, transvascular occlusion is unsuccessful or not possible and surgical ligation must be performed after all.

What to Expect: Prognosis and Recovery

Dogs and cats that have their PDA successfully corrected via one of the above procedures have an excellent prognosis for long-term survival and are expected to have a normal lifespan with no restrictions of any kind. Unfortunately, the majority of dogs and cats that do not undergo surgical ligation or coil occlusion go on to develop congestive heart failure during the first year of life, a condition which ultimately leads to death.

Signs to Watch For at Home

Many dogs and cats are asymptomatic at the time of diagnosis and should remain so following correction of the PDA. For dogs and cats diagnosed later in the course of disease or for those not corrected, symptoms may include lethargy, weakness, intolerance to activity or exercise, coughing, and rapid or labored breathing.

Observation of even the milder of these symptoms warrants a phone call to your veterinarian. More severe symptoms, such as difficulty breathing, require immediate attention on an emergency basis.

Moving Forward with Confidence

Learning that your pet has a heart condition can be frightening, but a PDA diagnosis comes with real hope. This is a condition that is well understood, and both treatment options have proven success rates. Dogs and cats that have their PDA corrected early are expected to live completely normal lives—running, playing, and bringing you joy for years to come. The key is moving forward with treatment before heart failure develops. Your veterinary team is here to guide you through every step of this journey and answer any questions you may have.