Our vets in Boulder are here to discuss Patent Ductus Occlusion (PDA) in dogs. It's an arterial shunt that occurs between the aorta and the pulmonary artery, which are the two major blood vessels leading from the heart. In this article, we will cover the symptoms, causes, and treatment options for PDAs in dogs.
What is Patent Ductus Occlusion?
There is a blood vessel called the ductus occlusion located between the main blood vessels of the heart, the aorta, and the pulmonary artery. This shunt is present in the fetus and allows most of the circulating blood to bypass the lungs and receive oxygen from the placenta. Normally, the ductus occlusion is open in the fetus while still in the mother's uterus.
After a puppy is born and takes their first breath, the ductus occlusion should naturally close to ensure that blood circulates properly through the now-inflated lungs and becomes oxygenated. However, in some cases, the ductus occlusion remains open, which can lead to health complications.
Patent Ductus Arteriosus Occlusion (PDA) In Dogs
A patent ductus arteriosus occlusion (PDA) is a defect in a puppy's heart that occurs when the ductus occlusion doesn't properly close at the animal's first breath at birth.
Usually, blood enters the right side of the heart before being pumped via the pulmonary artery into the lungs, which is oxygenated before entering the left side. After this, the left side of the heart pumps the blood through the aorta, carrying the oxygenated blood to the rest of the body. The left side of the heart usually has thicker, stronger muscles and higher pressure in both the right side and the pulmonary artery and veins. This is due to the fact that the left side works harder to pump blood to the whole body, compared to the right side pumping blood through the lungs.
If there is a defect or issue that prevents the ductus arteriosus from functioning properly, there will be a pressure difference between the pulmonary artery and the aorta. This will cause the blood to flow through the open ductus and into the pulmonary artery, which supplies the lungs, taking the path of least resistance. As a result, already-oxygenated blood circulates back to the lungs unnecessarily, reducing the amount of blood pumped to where it is required in the aorta. This places an additional burden on the left side of the heart as it tries to meet the body's demands.
The size of a heart defect can affect the amount of work the heart has to do. A minor defect may result in a slightly enlarged left ventricle, while a moderate-sized defect can cause more significant enlargement. As the heart works harder to supply oxygenated blood to the body, serious conditions like congestive heart failure may develop.
If the PDA is large in size, a larger amount of blood will go to the lungs, causing the pulmonary artery, pulmonary vein, and the right side of the heart to thicken in an attempt to handle the excess amounts of blood. This can lead to elevated blood pressure in the lungs (pulmonary hypertension) and can even cause reverse flow in the shunt.
Early Signs of Heart Disease in Dogs
When a dog has a small PDA defect, the symptoms may not be apparent initially. However, as the PDA grows, more blood flows through it, resulting in more noticeable symptoms. These symptoms may include:
- Difficulty breathing
- Loud heart murmur
- Abnormal pulses
- Intolerance for exercise
- A puppy with a PDA may sleep more than usual, be thinner or smaller in growth than average, or appear stunted in growth.
- Accumulation of fluid in lungs/abdomen (more advanced cases)
It is important to note that there are other complex heart conditions that can cause a heart murmur. Having your pet examined and tested (e.g., ECG) can help to differentiate between a PDA and a number of other potential issues.
If the condition of PDA remains undiagnosed or untreated, it can lead to irreversible damage to the heart muscle and eventually cause congestive heart failure. Advanced cases of PDA can also result in heart arrhythmia and noisy breathing when examined with a stethoscope.
When a shunt is oversized, it may cause the pressure in the pulmonary circulation to surpass that of the aorta. In such a situation, the shunt may invert, whereby blood travels through the aorta before proceeding to the lungs for oxygenation. This condition, known as 'reverse PDA,' causes heart murmurs to disappear, but other symptoms become more pronounced. In severe cases of 'reverse PDA,' the following symptoms may occur:
- Abnormal heartbeats
- Cyanosis (blueness) footpads on
- Hind leg collapse during exercise
- Weakness or lethargy
Are Some Dogs More At Risk For Developing A PDA?
It is more common for female dogs to develop PDAs than male dogs. Although this condition can affect any breed of dog, there is a higher likelihood of it being hereditary in smaller breeds. Some of these breeds that may be prone to this defect include:
- Shetland Sheepdogs
- English Springer Spaniels
- American Cocker Spaniels
- Bichon Frise
- German Shepherds
- Irish Setters
- Kerry Blue Terriers
- Labrador Retrievers
- Miniature and Toy Poodles
- Yorkshire Terriers
Since there appears to be a hereditary element to the defect, it is advised that dogs with this condition not be bred, even if they have been successfully treated for PDA. If your puppy or dog is showing signs indicating potential heart problems, as listed above, contact your veterinarian at once to book an examination.
Diagnosing PDAs In Dogs
When your vet listens to your puppy's chest during a routine physical check, they may hear a 'continuous' heart murmur (present during the entirety of the heart cycle, also called a 'washing machine murmur' due to its sound). There are two scales of grading heart murmurs in dogs: one is graded between 1–4 and 1–6. Using this scale, your veterinarian can have an idea of the severity of your dog's condition.
Your dog's chest will be X-rayed to more clearly see the heart and lungs more, and an electrocardiogram (ECG) is carried out to observe the heart rhythm. Blood tests may also be taken to ascertain whether other internal organs are being negatively affected by the abnormal blood flow or unusual red blood cell values.
Other tests, such as echocardiography (cardiac ultrasound), are needed to diagnose a PDA accurately. The technician can assess a moving image of the heart to observe the structure and functionality of the affected heart walls.
Treatment For PDAs In Dogs
The main focus of treating a PDA in a dog is stopping the blood from flowing through the shunt. Your primary vet will refer you to a veterinary cardiovascular surgeon, who can help to choose the best treatment for your dog's unique case. Whether the condition can be treated via heart surgery to tie off the ductus or a less invasive procedure to block off (occlude) the ductus with a special device, a vet specialist should perform a repair as soon as possible. If surgical treatment is delayed, it becomes more likely that there will be irreversible damage to the dog's heart.
Regrettably, there isn't a surgical solution for a reverse PDA. However, medical treatment can be used to manage the symptoms. It's important to note that the condition cannot be cured.
Success Rates For Surgical Treatment Of PDAs In Dogs
If your pet undergoes treatment prior to experiencing heart failure, the chances of surgical success are high, and they can return to their normal life. However, if there has been irreversible damage to the heart, your dog may require medication for their heart in the future.
Dogs With A Reverse PDA
If the symptoms associated with a reverse PDA can be controlled with vet-recommended medications, your dog can live in comfort for several more years.
In Conclusion ...
It is crucial to provide regular care for new puppies to detect heart conditions such as PDAs early and ensure prompt treatment. Our team at Boulder is dedicated to working with you to determine whether your dog requires surgical intervention or medical assistance and to promote your pet's overall health, well-being, and quality of life.
Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.