The Ductus Arteriosus
Between the aorta and the pulmonary artery (the two main blood vessels from the heart) is an arterial shunt called the ductus arteriosus. It usually develops along with the fetus, and it serves the purpose of allowing most of the circulating blood to bypass the lungs and supply the body with oxygen from the placenta. This means that while the fetus is still in the mother's uterus, the ductus arteriosus is usually open (patent).
When a puppy is born and takes their first breath, this stimulates the ductus arteriosus to close, ensuring the blood circulates normally through the now-inflated lungs and becomes oxygenated.
Patent Ductus Arteriosus (PDA) In Dogs
A patent ductus arteriosus (PDA) is a defect in a puppy's heart that occurs when the ductus arteriosus doesn't properly close at the animal's first breath at birth.
Normally, blood enters the right side of the heart before being pumped via the pulmonary artery into the lungs, where it is oxygenated before entering the left side of the heart. 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 because the left side works harder to pump blood to the whole body, compared to the right side pumping blood through the lungs.
If a defect or issue is preventing the ductus arteriosus, there is a difference in the pressure between the pulmonary artery and aorta, leading to blood taking the path of least resistance – from the aorta, through the open ductus and into the pulmonary artery that supplies the lungs. This means that this already-oxygenated blood is being circulated again to the lungs without reason, pumping less blood where it is needed in the aorta. The left side of the heart works harder to make up for the demands of the dog's body.
The size of the defect will have an impact on how much harder the heart works. A small defect can lead to a mildly enlarged left ventricle (mild left ventricular hypertrophy); a medium-sized defect causes a moderate enlargement in hearts, and as the organ works harder and harder to supply the body with oxygenated blood it can lead to serious conditions like congestive heart failure.
If the PDA is large, 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.
Symptoms Of PDAs In Dogs
If a dog has a small PDA defect, there may not be obvious signs of the condition at first. As the PDA increases in size, there is more and more blood shunting through it, leading to more obvious symptoms. These signs can 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 other complex heart conditions can cause a heart murmur. Having your pet examined and tested (e.g. ECG) can help to differentiate between a PDA and several other potential issues.
If the condition is not diagnosed or treated, blood will continue to shunt through the PDA, which can cause irreversible changes to the heart muscle and could later lead to congestive heart failure. If the PDA is this advanced, additional symptoms could also include heart arrhythmia, and noisy breathing when listened to with a stethoscope.
If the shunt is quite large, the pulmonary circulation pressure could increase until it is more than the pressure in the aorta. If this occurs, the shunt might reverse – this means that blood returning from the body takes a shortcut through the aorta before continuing to the lungs for oxygenation. This 'reverse PDA' causes the symptoms of heart murmurs to disappear, but others to become significantly more severe. Advanced cases and/or 'reverse PDA' can cause the following symptoms:
- Abnormal heartbeats
- Cyanosis (blueness) footpads on
- Hind leg collapse during exercise
- Weakness or lethargy
Are Some Dogs More At Risk For Developing A PDA?
Female dogs tend to develop PDAs more commonly than male dogs, and although it can affect any dog breed it seems to have an element of heritability in smaller dog breeds. Some breeds that may be prone to this defect include:
- Maltese
- Pomeranians
- Shetland Sheepdogs
- English Springer Spaniels
- American Cocker Spaniels
- Keeshonden
- Bichon Frise
- German Shepherds
- Collies
- Irish Setters
- Kerry Blue Terriers
- Labrador Retrievers
- Newfoundlands
- Miniature and Toy Poodles
- Chihuahuas
- 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 see the heart and lungs, and an electrocardiogram (ECG) will be carried out to observe the heart rhythm. There may also be blood tests taken to ascertain whether other internal organs are being negatively affected by abnormal blood flow or unusual red blood cell values.
Other tests such as echocardiography (cardiac ultrasound) are needed to accurately diagnose a PDA. 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 repair should be performed by a vet specialist as soon as possible. If surgical treatment is delayed, it becomes more likely that there will be irreversible damage to the dog's heart.
Unfortunately, there is no surgical treatment for a reverse PDA. The symptoms can be managed with medical treatment, but the condition is not curable.
Success Rates For Surgical Treatment Of PDAs In Dogs
If your pet receives treatment before having experienced heart failure, the rate of success associated with surgery is quite high, and the majority of them can return to normal life. If irreversible heart damage has already occurred, your dog might need to be on heart medication 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.
Supporting Your Dog's Heart Health
Routine care for new puppies is important for diagnosing heart conditions like PDAs early so that they can be treated. Whether your dog is eligible for surgical intervention or medical support, our Englewood team will work with you to support your pet's health, comfort, 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.