Pulmonary atresia (PA) is a serious congenital heart defect where the pulmonary valve, which controls blood flow from the heart to the lungs, fails to develop properly. This condition is present at birth, typically resulting in a complete blockage that prevents blood from flowing out of the heart’s right ventricle and into the pulmonary artery. This blockage severely limits the body’s ability to oxygenate blood, making immediate medical intervention necessary for survival. PA is therefore considered a cyanotic heart disease.
Understanding the Heart Defect
The fundamental problem in pulmonary atresia is the obstruction of the pulmonary valve, a structure normally situated between the right ventricle and the pulmonary artery. In a healthy heart, the right ventricle pumps oxygen-poor blood through this valve to the lungs for gas exchange. With PA, the fused or absent valve leaflets create a solid barrier, forcing the blood to find an alternate route to the systemic circulation.
To survive, a newborn with pulmonary atresia must rely on two temporary circulatory structures that are supposed to close shortly after birth. The patent ductus arteriosus (PDA), a vessel connecting the aorta and the pulmonary artery, provides the only reliable path for blood to reach the lungs. An opening between the upper chambers (foramen ovale or atrial septal defect) allows oxygen-poor blood from the right atrium to bypass the right ventricle and mix with oxygenated blood in the left side of the heart.
Pulmonary atresia is categorized into two main anatomical types based on the ventricular septum.
Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)
PA/IVS occurs when the wall separating the right and left ventricles is whole. In these cases, the right ventricle often becomes underdeveloped (hypoplastic) because it receives little blood flow before birth. This anatomy typically necessitates a single-ventricle repair approach.
Pulmonary Atresia with Ventricular Septal Defect (PA/VSD)
In PA/VSD, a hole exists in the wall between the two lower chambers. This defect allows blood to flow between the ventricles, which often helps the right ventricle develop to a more normal size. The presence of a VSD means that a two-ventricle repair, aiming to restore normal blood flow, may be possible.
Developmental Origins
Pulmonary atresia occurs during the first eight weeks of fetal development when the heart structure is forming. While the precise cause for most cases remains unknown, the condition is believed to arise from a combination of genetic and environmental factors. Most instances are sporadic, meaning they occur randomly without a clear inheritance pattern.
Risk factors include maternal conditions such as poorly controlled diabetes and the use of certain medications known as teratogens. A family history of congenital heart defects can also slightly increase the risk. Genetic abnormalities, such as certain chromosomal defects, have been linked to a small percentage of cases. However, for the majority of affected infants, the condition develops by chance due to an error in the complex process of cardiac development.
Identifying Pulmonary Atresia
Symptoms of pulmonary atresia typically appear immediately or within the first few hours or days after birth as the ductus arteriosus begins to narrow naturally. The most noticeable sign is cyanosis, a bluish tint to the skin, lips, and nail beds, caused by the low oxygen levels in the circulating blood. Other common symptoms include rapid or troubled breathing, fatigue, and difficulty feeding.
The diagnostic process often begins with a prenatal assessment if the defect is suspected during a routine ultrasound. A fetal echocardiogram, which is a detailed ultrasound of the baby’s heart, can confirm the diagnosis before birth. After delivery, a physical examination may reveal a heart murmur, although this is not always present.
The primary diagnostic tool used postnatally is the echocardiogram, which uses sound waves to create a moving picture of the heart structure. This test confirms the atretic pulmonary valve and assesses the size of the right ventricle and the flow through the patent ductus arteriosus. Other tests, such as pulse oximetry screening, chest X-rays, and cardiac catheterization, provide additional details about blood oxygen saturation, heart size, and the architecture of the pulmonary arteries.
Treatment Strategies
Immediate medical stabilization is required due to the infant’s dependence on the patent ductus arteriosus (PDA) for pulmonary blood flow. The first line of treatment is a continuous intravenous infusion of Prostaglandin E1 (PGE1). This medication prevents the PDA from closing, maintaining the pathway for blood to reach the lungs to receive oxygen.
Surgical intervention is necessary to provide a durable source of blood flow to the lungs. The specific surgical strategy depends entirely on the baby’s anatomy, particularly the size of the right ventricle (RV). If a two-ventricle repair is possible, the goal is to create a functional connection between the RV and the pulmonary artery, often involving a shunt or a patch, and closing any associated defects like a VSD.
If the right ventricle is too small to function as a pumping chamber for the lungs, a staged single-ventricle palliation approach is necessary. This multi-step process aims to redirect all the oxygen-poor blood directly to the lungs, bypassing the right ventricle entirely. The first stage is often the placement of a systemic-to-pulmonary shunt, such as a Blalock-Taussig shunt, to provide a temporary, regulated source of blood flow to the lungs.
The single-ventricle palliation involves two further stages. The second stage, typically performed between four and twelve months of age, is the Glenn procedure, which connects the superior vena cava directly to the pulmonary artery. This redirects blood from the upper body directly to the lungs. The final stage, usually completed between two and four years of age, is the Fontan procedure, which connects the inferior vena cava to the pulmonary artery, completing the bypass of the right ventricle.
Long-Term Outlook
The prognosis for individuals treated for pulmonary atresia has improved due to advancements in surgical techniques and postnatal care. Survival into adulthood is common, but it requires lifelong specialized follow-up care. The long-term outcome is highly dependent on the initial anatomy and the success of the chosen repair pathway, whether it is a two-ventricle repair or a Fontan palliation.
Individuals with PA must remain under the care of a cardiologist specializing in Adult Congenital Heart Disease (ACHD) to monitor for complications. Potential long-term issues can include heart rhythm problems, known as arrhythmias, and a weakening of the heart muscle, which may lead to heart failure over time. Subsequent surgeries or catheter-based procedures may be necessary decades later to replace failing valves or conduits.
Even after successful intervention, regular testing, including echocardiograms and cardiac MRIs, is necessary to assess heart function and the condition of the pulmonary arteries. While the life expectancy is generally positive for those who reach the completion of their staged treatment, vigilance and proactive management are required to address the unique challenges associated with a repaired congenital heart defect.