Pulmonary atresia (PA) is a complicated congenital (present at birth) defect that occurs due to abnormal development of the fetal heart during pregnancy.
The pulmonary valve is found between the right ventricle (RV) and the pulmonary artery. It has three leaflets that function like a one-way door, allowing oxygen depleted blood to flow from the right pumping chamber (RV) out to the lungs to pick up oxygen. This valve closes as the RV relaxes so that blood does not go backwards into the right ventricle. With pulmonary atresia, problems with valve development prevent the leaflets from opening, therefore, blood cannot flow forward from the right ventricle to the lungs.
Pulmonary atresia occurs in about one out of every 10,000 live births.
PA occurs as the heart is forming during the first 8 weeks of fetal development. Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality, or environmental exposure, causing heart problems to occur more often in certain families. Most of the time, this heart defect occurs sporadically (by chance), with no clear reason for its development.
Before birth, while the fetus is developing, the placenta provides oxygen for the baby and the lungs are not being used to oxygenate the blood. Blood entering the right side of the fetal heart passes through an opening called the foramen ovale that allows oxygen-rich (red) blood from the placenta to pass through to the left side of the heart and proceed to the body. In some cases, there may be a second opening, this time in the ventricular wall, that allows blood in the right ventricle a way out. This opening is called a ventricular septal defect (VSD). If there is no VSD, the right ventricle receives little blood flow before birth and does not develop fully.
At birth, when the baby is separated from the placenta, the lungs open on the first breath and now must do the work of oxygenating the baby’s blood. However, with no pulmonary valve opening present, blood must find another route to reach the lungs and receive oxygen. The foramen ovale normally shuts at birth, but may stay open in this situation, allowing oxygen-poor (blue) blood to pass from the right atrium to the left atrium. From there, it goes to the left ventricle, out the aorta, to the body. This situation cannot support life, since blue blood cannot meet the body’s demands for oxygen. Newborns also have a connection between the aorta and the pulmonary artery, called the ductus arteriosus, that allows some of the blue blood to pass into the lungs. Unfortunately, this ductus arteriosus normally closes within a few hours or days after birth.
Cyanosis (blue color) is often present to some degree immediately after birth. Depending on other structural differences in the heart, it could range from mild to profound. The degree of cyanosis is related to the presence of other defects that allow blood to mix. These defects include:
- A patent (open) ductus arteriosus – used to bypass the lungs during fetal life. This ductus arteriosus begins closing shortly after birth. Closure is prompted by the introduction of oxygen into the blood once the baby starts breathing on it’s own. Closure of this ductus starts within hours of being born and can take a few days to a few weeks. As the vessel closes the cyanosis will increase.
- Collateral vessels – extra blood vessels that take blood from an artery to the lungs. Depending on the size of these vessels, the baby may not be blue as early and may not need a surgical intervention for a longer period. Eventually, however, the baby will outgrow the capacity of these vessels to get enough blood to the lungs for oxygenation.
The following are the most common symptoms of pulmonary atresia. However, each child may experience symptoms differently. Symptoms may include:
- Rapid breathing
- Difficulty breathing
- Pale, cool, or clammy skin
The symptoms of pulmonary atresia may resemble other medical conditions or heart problems.
This heart defect is often picked up before birth, during an ultrasound. Your obstetrician will refer you to a specialist who will perform a fetal echocardiogram. This can give you a chance to learn about this defect, and also helps your doctors prepare for the birth of your baby. When this diagnosis is known before birth, the baby can be stabilized with a medicine that can keep the fetal connections open until the baby is thoroughly examined and has an echocardiogram to confirm whether the baby will need surgery in the newborn period.
Specific treatment for pulmonary atresia will be determined by your child’s physician based on:
- Your child’s age, overall health, and medical history
- Extent of the disease
- Your child’s tolerance for specific medications, procedures, or therapies
- Expectations for the course of the disease
At first, the child will need to be admitted to the intensive care unit and possibly placed on oxygen and a ventilator that will help the child breathe. IV medications that assist the heart and lung function may be given. An IV medication called prostaglandin E1 stops the ductus arteriosus from closing, allowing mixing of the pulmonary and systemic circulations.
Another preliminary treatment is heart catheterization. It is used to evaluate the defect or defects of the heart; this procedure is much more invasive.
Ultimately, however, the patient will need to have a series of surgeries to improve the blood flow permanently. The first surgery will likely be performed shortly after birth. A shunt can be created between the aorta and the pulmonary artery to help increase blood flow to the lungs. As the child grows, so does the heart and the shunt may need to be revised in order to meet the body’s requirements.
The type of surgery recommended depends on the size of the right ventricle and the pulmonary artery. If they are normal in size and the right ventricle is able to pump blood, open heart surgery can be performed to make blood flow through the heart in a normal pattern. If the right ventricle is small and unable to act as a pump, doctors may perform another type of operation called the Fontan procedure. In this two-stage procedure, the right atrium is disconnected from the pulmonary circulation. The systemic venous return goes directly to the lungs, by-passing the heart.