Patent Ductus Arteriosus: PDA in Dogs

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Patent ductus arteriosus (PDA) is a heart condition in dogs. It's more common in female than male dogs and occurs most often in small or toy breeds.

What Is Canine PDA?

PDA occurs when a duct connecting the two main blood vessels of the heart, the descending aorta and the pulmonary artery, doesn't close like it should when the dog is born.

As a fetus, the pup gets oxygen for all the tissues through the placenta, and the lungs aren't working yet. So, most of the circulating blood goes around (bypasses) the lungs by going through the ductus arteriosus. When a puppy begins breathing air and using the lungs at birth, the ductus arteriosus normally closes, so the blood can pass through the lungs and get oxygenated.

When the ductus arteriosus does not close as it should at birth, blood goes through it and is directed back to through the lungs when it doesn't need to. That leaves the left side of the heart working harder to pump enough oxygenated blood to the body, and the result, eventually, is left-sided heart failure.

A PDA can be small or huge, and its size contributes to how enlarged the heart becomes.

Signs of PDA in Dogs

Signs of a patent ductus arteriosus in dogs include:

• Coughing
• Exercise intolerance
• Loud heart murmur
• Stunted growth

As the shunt worsens or if it is very large, it may reverse and become right to left. In that case, the blood gets sent back out to the body without first picking up oxygen in the lungs. There is no murmur in the case of a reverse PDA, but the dog may have blue skin on the paws, a weak hind end, and collapse.

Diagnosis of PDA in Dogs

PDA is usually diagnosed by a veterinarian who hears the classic murmur through a stethoscope. It is described as a machinery murmur and sounds like a loud washing machine. X-rays of the chest may reveal an enlarged heart, especially the left side. An echocardiogram may allow the vet to visualize the PDA as well as determine how much the heart activity is affected by it. It is not unusual for a puppy with PDA to have other congenital heart defects as well, and echocardiography can help diagnose those too.

Treatment of PDA in Dogs

Surgery is the usual way of treating a PDA. A suture is used to close the abnormally open duct. Most of the time, this surgery requires a veterinary cardiology specialist to perform.

If a dog is in congestive heart failure, that will need to be treated and controlled before surgery.

Devices that can block or occlude the patent ductus arteriosus can be delivered into the open duct through a heart catheter. This is less invasive than suturing the duct but will still likely require a specialist to perform, and it may not be possible on tiny dogs or those with large PDAs.

If reverse PDA has occurred, surgery is not an option to correct it. The only treatment is to thin the blood, which becomes thick during the condition.

The prognosis for dogs with PDA treated surgically or with an occlusion device is good if the correction is done before heart failure develops. The prognosis for dogs with reverse PDA is poor long-term.

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