Pulmonary atresia is a developmental defect that mainly affects the valve between the right cardiac ventricle and the pulmonary artery. In patients suffering from pulmonary atresia, the valve remains closed and blood flow from the right ventricle into the pulmonary artery is interrupted.
PA is a cardiac malformation that leads to severe consequences immediately after birth. Thus, it is commonly diagnosed within hours after birth. Children may be born cyanotic and their condition does not improve with oxygenation. Their skin is usually pale, clammy, and sometimes even cool.
Additional symptoms may be present right from the beginning and may aggravate when the ductus arteriosus closes or the symptoms may manifest only after closure of the ductus. Physiologically, the ductus arteriosus closes during the first days of life. However, there is an increased risk for patent ductus arteriosus in PA patients. Symptoms result from restricted oxygen supply to the whole body and generally consist of tachycardia, tachypnea, and dyspnea. An affected child tends to demonstrate feeding difficulties and fatigue. All these symptoms are not specific for either cardiovascular or respiratory problems.
Symptoms present at birth or shortly after with severe cardiovascular or respiratory distress. If a child is born with cyanosis and this condition does not normalize within a very short time span, diagnostic measures need to be taken to identify its cause.
While arrhythmias may be detected in an electrocardiogram, echocardiography will directly visualize the defect pulmonary valve. If additional malformations such as a ventricular septal defect are present, these may also be seen in an echocardiographic examination.
If radiographic images will reveal a slightly enlarged heart. More striking may be the lack of or abnormal appearance of pulmonary vascular structures. Collaterals may be visible in the form of speckled areas. If pulmonary vessels seem to be well developed on one side and appear abnormal on the other, then the problem might be at the level of one of the two pulmonary arteries rather than cardiac. Pulmonary artery stenosis can then be considered in differential diagnosis.
Magnetic resonance imaging may help to further determine the vascular anatomy of the heart, lungs and surrounding tissues . This may be facilitated by administering intravenous contrast agents . A precise definition of the individual case is essential before planning surgical treatment.
Such pre-surgical information may be supplemented by results of cardiac catheterization.
Treatment depends on the overall condition of the child, on the extent of the disease and the individual development of pulmonary arteries and collaterals. Treatment needs to be initiated as soon as possible since an untreated PA may be fatal within a few days.
To gain some time, the closure of the ductus arteriosus is prevented by administering prostaglandin E1 intravenously immediately following diagnosis. In children with PA, an atrial septal defect favors circulation and passage of blood low in oxygen to the left atrium and finally to the ductus arteriosus, the foramen ovale may be dilated in a procedure called balloon atrial septostomy. It may be performed via cardiac catheterization and does not require open surgery.
These treatments provide only short term relief. Surgical interventions are necessary to restore physiological heart function. There are different options that may be considered depending on the existence of a ventricular septal defect and development of pulmonary arteries. The former may prove beneficial for limited periods of time, the latter may be stimulated by increasing blood flow through the respective vessels. Certain interventions may only be carried out at a later time because pressure ratios do not favor them initially. Also, staged procedures are much better tolerated than one stage, major surgeries .
For instance, the pulmonary valve and parts of the pulmonary artery may be transplanted in the form of a homograft. If such treatment cannot be performed then a shunt may be temporarily placed between the right ventricle and the pulmonary artery. This shunt is removed in a second surgery that takes place when the child is approximately six months old. During that same intervention, the superior vena cava is connected to the pulmonary artery (hemi-Fontan procedure). This connection allows the blood to bypass the right heart. The same child needs to undergo a third surgery between the age of 3 to 6 years. During the third surgery the inferior vena cava is connected to the pulmonary artery (Fontan completion). Other surgical approaches may be chosen depending on the individual case.
Prognosis depends on the individual case, but is generally good if adequate treatment is provided. Depending on the extent of malformation, several surgeries may be required to ensure optimal heart function and oxygen supply to the body . However even after surgical correction patients should undergo regular follow-ups during their lifetime.
The exact etiology of PA is not known. However, genetic factors seem to play a role in this and other cardiac developmental disorders. This hypothesis is supported by the fact that the risk for such diseases is increased in siblings of affected patients and in children born to parents who have been diagnosed with cardiac malformations themselves .
There is a high incidence of patent ductus arteriosus among PA patients. Furthermore, this malformation has been associated with a variety of other congenital defects, e.g., Alagille syndrome, DiGeorge syndrome, Down syndrome and VACTERL association (vertebral anomalies, anal atresia, cardiac defects, tracheoesophageal fistula, esophageal atresia, renal anomalies and limb defects).
The overall incidence of PA has been estimated in several studies and seems to range between 5 and 15 per 100,000 births   . PA only accounts for a small subset of congenital cardiac malformations  .
With regards to gender distribution, males seem to be affected slightly more than females.
Development of the pulmonary arteries, potential collaterals and the ductus arteriosus depends on demands for blood flow and as PA patients maintain pulmonary circulation by means of different blood vessels, distinct anatomical situations may be encountered in these individuals.
Poorly oxygenated blood may reach the lungs via native pulmonary arteries in this condition. Due to PA there is no direct connection between the right ventricle and these arteries and a patent ductus arteriosus may supply blood to the latter. If the ductus arteriosus closes, there may be major aortopulmonary collaterals that lead aortic blood into native pulmonary arteries. While most collaterals originate from the thoracic aorta, the existence of branches of bronchial, pleural or mammary arteries that serve as pulmonary collaterals has been described. In rare cases, collaterals may originate from coronary arteries . If blood flow to the pulmonary trunk or to both pulmonary arteries is assured by a patent ductus arteriosus or collateral arteries, pulmonary vessels usually develop normally.
However, not all collaterals do necessarily connect to pulmonary arteries. They may instead reach the lungs themselves. Here, intrapulmonary vessel development will be altered.
In some cases, collaterals are the only vessels supplying the lungs with blood. If native pulmonary arteries have never been connected to the cardiovascular system, they do not develop and are virtually absent. Patients presenting this last anatomic situation are often diagnosed with pulmonary artery atresia to distinguish their condition from that of local PA, which mainly affects the pulmonary valve.
A significant number of patients with collateral arteries supplying blood to the pulmonary circulation also present with some degree of stenosis of these arteries. Stenosis often progresses over time.
Detailed knowledge about the individual development of pulmonary arteries, collaterals and ductus arteriosus is of utmost importance before deciding on surgical intervention. Also, the clinical presentation of the patient depends on their individual developmental disorder.
No measures can be recommended to prevent PA.
In healthy individuals, blood flow from the cardiac ventricles into the aorta and pulmonary artery occurs during ventricle contraction or systole. Aortic and pulmonary valves mark the limits of the left and right cardiac ventricle, respectively, and are open during this stage of the cardiac cycle. In order to enable subsequent filling of the ventricles, the myocardium relaxes and the respective valves close.
In patients suffering from pulmonary atresia (PA), the pulmonary valve remains closed because the orifice between its three leaflets is undeveloped. Thus, the blood flow from the right ventricle to the pulmonary artery is interrupted. This condition can be lethal if blood flow towards the lungs is not established via alternative routes. Prior to birth and in healthy fetuses, blood flows from the pulmonary artery through the ductus arteriosus directly into the aorta, thus bypassing the lungs. This ductus physiologically closes during the first days or weeks after birth. In PA patients it may persist in the form of a patent ductus arteriosus that allows blood flow from the aorta to the pulmonary artery. While a significant number of patients have pulmonary circulation via native pulmonary arteries, others develop major aortopulmonary collateral arteries. A combination of both pulmonary arteries and aortopulmonary collaterals have also been observed.
PA may be present as a single cardiac malformation or may be associated with a ventricular septal defect. In even more severe cases, PA occurs as part of a complex cardiac malformation . Here, an abnormally small size of right cardiac structures can be observed. Underdevelopment of the right ventricle and related structures can result from disuse. PA and associated heart defects may be diagnosed prenatally using fetal echocardiography.
In order to understand the condition of pulmonary atresia (PA), basic background knowledge regarding heart function is essential. There are four chambers in the heart and the two main chambers are called ventricles. The left ventricle is connected to the aorta and pumps blood rich in oxygen throughout the whole body. After cells and tissues use the oxygen, the blood is transported back to the heart via veins. The blood then reaches the right side of the heart and finally the right ventricle which is connected to the pulmonary artery and pumps blood into the lungs where it will be oxygenated before it reaches the left side of the heart.
In between the right ventricle and the pulmonary artery there is the pulmonary valve. This valve needs to open and close during regular heart pumping. However, in patients suffering from PA, this valve cannot open and the blood flow between the right ventricle and the pulmonary artery is interrupted. For the patient to survive, blood needs to find alternative ways to reach the lungs and tank oxygen. In some patients, vessels persisting from fetal life fulfill this task; in others, collateral vessels developed in utero perform this function.
The exact causes of PA are not known. The disease is congenital, i.e., it exists at the time of birth. Presumably, genetic factors play an important role: in certain families there are several cases of cardiac malformation. PA is sometimes associated with other heart defects such as an incomplete closure of the ventricular septum.
Due to the severity of the defect, symptoms often manifest immediately after birth. Children may be born cyanotic, i.e., with a bluish discoloration of their skin. Their skin may feel cool and clammy. Because of poor oxygen supply to the body, they may present with an accelerated heart rate, difficulty breathing and difficulties while feeding.
Heart murmurs can be heard easily using a stethoscope. An abnormal heart rhythm will be detected when recording an electrocardiogram. Echocardiography, an ultrasound examination of the heart, allows direct visualization of the underdeveloped pulmonary valve and other cardiac malformations if present.
Imaging studies such as X-rays and magnetic resonance imaging may reveal a slightly enlarged heart and abnormal formation of pulmonary vessels. The latter results from little use due to interruption of pulmonary circulation at the pulmonary valve.
Precise information regarding the individual vascular development of the child are necessary before any surgical intervention is planned.
Initially, prostaglandin E1 may be administered to avoid closure of the ductus arteriosus, one of the above mentioned vessels that persist from fetal development and that may actually benefit a child suffering from PA. Also, a patent opening between the right and left atrium may be artificially dilated to improve circulation while awaiting surgery.
In less severe cases, the underdeveloped valve may be replaced with a homograft, i.e., a transplant obtained from an organ donor. Other children require more complex re-connection of major veins to the pulmonary arteries so the blood may bypass the right ventricle.
The overall prognosis is good if adequate treatment is provided in a timely manner. However, multiple surgeries are often necessary to reconstruct a functioning heart that may supply oxygen to the whole body. Regular follow-ups are needed for a lifetime.