Patent Ductus Arteriosus
In order to understand this disease, it is first important to understand normal blood flow through the heart. Blood drains from the body into the right collecting chamber (the right atrium). It then passes through the tricuspid valve into the right pumping chamber (the right ventricle). From here, blood is pumped via the pulmonary artery to the lungs to receive oxygen. Oxygenated blood then drains into the left atrium, through the mitral valve and into the left ventricle. From here, it is pumped via the aorta to deliver oxygenated blood to all tissues of the body.
What is Patent Ductus Arteriosus?
In the developing foetus, blood entering the right heart is already well oxygenated as it is coming via the mother’s placenta. Hence, blood does not need to pass through the foetus’s lungs to pick up oxygen. There are a number of mechanisms in place that allow the blood to bypass the lungs in the foetus. One of these is a vessel called the ductus arteriosus. The ductus arteriosus is a small vessel that connects the pulmonary artery (the vessel that takes the blood to the lungs) to the aorta (the vessel taking oxygenated blood to the body). The ductus arteriosus should start to close at birth and is normally completely closed by 3 days. Occasionally this does not happen and the ductus arteriosus remains open or ‘patent’.
Once born, blood flows from the high pressure aorta to the low pressure pulmonary artery, to the lungs and back to the left side of the heart. Over time, the extra blood flow to the lungs and left heart causes these chambers to increase in size. If left uncorrected, congestive heart failure (fluid in the lungs) is the result. In 65% of dogs this occurs by 1 year of age.
How Do I Know if my Puppy has a PDA?
Physical examination: Your regular veterinarian will usually pick up a heart murmur at the first puppy check. A PDA has a very characteristic murmur called a ‘continuous’ murmur. This murmur sounds like a washing machine. 99% of the time a puppy with this kind of murmur has a PDA.
Echocardiogram (heart ultrasound): An echocardiogram is essential to confirm the initial physical exam diagnosis of a PDA. The echocardiogram allows visualisation of the PDA, assessment of chamber enlargement and any potential complicating factors that may affect your puppy’s treatment.
Chest Xrays: Chest xrays may be recommended if your puppy’s heart is already very large or if he/she has any respiratory signs. This is the best way to evaluate the lungs for evidence of congestive heart failure (pulmonary oedema).
Electrocardiogram (ECG): Occasionally an ECG will be recommended to evaluate your puppies’ heart rhythm.
How is PDA Treated?
Surgery was the traditional method of repair. In a PDA surgery, the chest is opened, the PDA carefully dissected free from the surrounding vessels and a piece of suture is used to tie off the patent vessel. This surgery requires a specialist surgeon with complication rates of < 10% in experienced hands. In more recent times, a non-invasive method of correction is preferred. In this method, a small nickel-titanium plug (called an Amplatz Canine Ductal Occluder) or a small metal coil is delivered via a catheter to plug up the PDA. The catheter is usually delivered via the femoral artery. Transvascular occlusion has the advantage of not having to open the chest. Hospital stay and postoperative medications are minimized with this approach, however, it is often not feasible to use this approach in very small puppies due to the small size of their femoral artery. In this situation, open chest surgery is usually recommended.
Amplatz Canine Ductal Occluder
Treatment is nearly always recommended for PDA as, if left uncorrected, 65% of puppies will die of heart failure by 1 year of age. If corrected and the surgery or procedure is successful, your puppy should go onto live a completely normal life.