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 Patent Ductus Arteriosus (PDA): A Parent's Guide






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Patent Ductus Arteriosus (PDA): A Parent's Guide

Written by:
Robert J. Sommer, M.D.
Associate Professor of Pediatrics
Director, Pediatric Cardiac Catheterization Laboratory
Division of Pediatric Cardiology
Mount Sinai Medical Center
New York, New York

Edited by: Mona Barmash

What is a PDA?

The ductus arteriosus is a normal part of the circulation of the fetus. It is a blood vessel that connects the two large arteries coming out of the heart, the aorta and the pulmonary artery.

Blood coming out of the right ventricle has a choice. It can flow to the lungs, as it will later in life, or it may flow across the ductus arteriosus to the aorta and back to the placenta.

Since there is fluid and no air in the fetal lungs, there is little need for blood to flow in that direction. Thus, in the fetus, the ductus allows blood from the right side of the heart to bypass the non-functioning lungs.

With the baby's first breath, the lungs fill with air and become the source of oxygen for the newborn once the umbilical cord is cut. At that moment, the blood from the right ventricle changes course, and begins to flow to the lungs. The ductus is no longer necessary for diverting blood from the lungs. Some blood from the aorta may cross the PDA to also help fill the lungs.

The ductus itself is a blood vessel lined with muscles, which serves a specific function. When the level of oxygen in the blood rises (this usually happens immediately after birth), the muscles contract, squeezing closed the ductus. In the first 48 to 72 hours of life, more than 95% of all babies have a closed ductus. Once the ductus is closed, the blood from the right side of the heart only travels to the lungs, as is the case in the adult circulation.

In some children, the ductus does not close, or remains partially open. This is due to either an absence of the normal oxygen sensors in the ductus muscle, or a weakness of the muscle which does not allow complete closure. When the ductus does not close within the first few days of life, it is called a persistently Patent Ductus Arteriosus (PDA). Patent means open.

Why is a PDA important?

In the normal newborn, the lungs mature over the first few weeks of life. With this maturation, the blood pressure in the lungs falls rapidly compared with the blood pressure in the rest of the body.

In the child with a PDA, blood flowing through the aorta has a choice. It can either flow forward into the body against the normal high blood pressure, or it can flow across the PDA to the low pressure in the lungs. Since it is easier for the blood to flow to the lungs, blood will preferentially flow in that direction, and mix with the normal blood coming out of the right heart.

The amount of additional blood reaching the lungs depends on the size of the ductus itself. If it is very small, for example when the ductus muscles did not close the vessel completely, little extra blood can squeeze through the PDA. In this case, the child will have no symptoms at all, and will appear to be perfectly healthy.

The small PDA will likely only be discovered when the pediatrician detects a "heart murmur", an extra heart sound created when the blood squirts through the small opening of the PDA. The sound the doctor is hearing is similar to the sound created by water flowing through the end of a garden hose when the opening is partially covered by a finger. A small PDA like this can be discovered at any age. The smaller the opening, the less flow goes through the vessel, and the softer the sound of the heart murmur. The smaller the opening the more likely it is to be undetected at an early age, even though it has been present since birth.

If the PDA is large, an enormous amount of additional blood may "flood" the lungs. These children are often quite sick in the first few days or weeks of life, with symptoms of poor feeding, poor weight gain, constant sweating, hard breathing and fast heart rate. The cardiologist and neonatologist refer to these symptoms when they use the term "congestive heart failure". Congestive heart failure is most often seen in premature infants in the hospital. These babies often require treatment before they leave the hospital.

While children with small PDA's do not face the risk of congestive heart failure, even patients with a tiny PDA are at risk of another problem called endocarditis. Endocarditis is literally an infection of the heart, its valves, or its blood vessels. It is a potentially life-threatening illness which may be associated with death, stroke, and cardiac dysfunction.

Endocarditis occurs when germs in the baby's bloodstream stick at the site of a heart abnormality. A local infection is therefore established as the germs grow and multiply. Under normal circumstances, the heart, its valves and its vessels are protected from this infection by a smooth inner lining which keeps the blood cells and germs from attaching. When blood flow is turbulent or rough, due to the jets of blood squirting through the PDA under high pressure from the aortic side, the smooth lining of the vessels around the PDA can be disrupted. This helps the germs to stick to the walls of the vessels. As long as the PDA is present, the patient remains at risk of endocarditis. This risk has been estimated at 0.5% per year for the life of the patient. In other words, over a 100 year lifespan, there is a 50-50 chance of getting endocarditis at least once.

Antibiotic treatment before dental and other minor surgical procedures has helped to eliminate the risk of endocarditis for the patients with PDA. Once the PDA is closed, by either surgical or transcatheter techniques (see below), antibiotic pre-treatment for procedures may be discontinued 6 months after closure. During that six month period, the smooth lining of the blood vessel grows over the surgical or catheter site. Thereafter, the blood flowing past that area cannot distinguish this smooth surface from the normal blood vessels.

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