Pulmonary atresia

Pulmonary atresia is a congenital malformation of the pulmonary valve in which the valve orifice fails to develop. The valve is completely closed thereby obstructing the outflow of blood from the heart to the lungs. The pulmonary valve is located on the right side of the heart between the right ventricle and pulmonary artery. In a normal functioning heart, the opening to the pulmonary valve has three flaps that open and close like one way doors. As these flaps open and close they allow blood to flow forward into the pulmonary artery and on to the lungs where the blood becomes oxygenated, and prevent backward flow into the right ventricle. With the disease pulmonary atresia, the flap-like openings are completely covered by a layer of tissue, thus preventing the ability of blood flow to the lungs to become oxygenated. The body requires oxygenated blood for survival. Pulmonary atresia is not threatening to a developing fetus however, because the mother's placenta provides the needed oxygen since the baby's lungs are not yet functional. Once the baby is born its lungs must now provide the oxygen needed for survival, but with pulmonary atresia there is no opening on the pulmonary valve for blood to get to the lungs and become oxygenated and the only source of pulmonary blood flow is a patent ductus arteriosus. Due to this, the newborn baby is blue in color and pulmonary atresia can usually be diagnosed within hours or minutes after birth.

Classification

There are two types of pulmonary atresia.

Pulmonary Atresia with Intact Ventricular Septum (PA-IVS)

PA-IVS is a rare congenital lesion. This lesion can be diagnosed during the fetal stage of life by using fetal echocardiography, which is a test that uses sound waves to look at the structure of an unborn baby's heart. PA-IVS involves complete blockage of the pulmonary valve located on the right side of the heart. This blockage thus prevents the flow of blood to the lungs. Because of this lack of blood flowing through the right side of the heart, the structures on that side, such as the pulmonary valve and the tricuspid valve, are abnormally small. The genetic cause of PA-IVS is unknown. It is rare, occurring in around 4-6 cases per every 100,000 live births.^[1]

Pulmonary atresia with Ventricular Septal Defect (PA-VSD)

This lesion is identified by underdevelopment of the right ventricle. The Ventricular Septal Defect (VSD) is a second opening in the ventricular wall, which provides a way out for blood in the right ventricle. When this second opening does not exist, very little blood goes to the right ventricle, which is what causes it to be underdeveloped in PA-IVS. This defect can also be determined before birth. Out of all congenital cardiac malformations, it is estimated that PA-VSD occurs in 2.5-3.4% of the cases. The genetic cause of PA-VSD is not known; it is found however, that children whose parents have PA-VSD are at a higher risk for congenital heart lesions.

Cause

Doctors are unsure of the cause of congenital heart defects, but there are some medical conditions that have been found to increase the risk of having a baby with a heart defect such as congenital heart disease in the mother, father, brother, or sister of the baby, a diabetic mother, use of drugs or alcohol or over the counter prescriptions during pregnancy. These conditions do not mean that the baby will definitely be born with a heart defect, but that it runs a higher chance. Sometimes babies are born without any of these conditions; the cause is unknown.

Treatment

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. Also, IV medications that assist the heart and lung function may be given. An IV medication called prostaglandin E1 is used for treatment of pulmonary atresia, as it stops the ductus arteriosus from closing, allowing mixing of the pulmonary and systemic circulations. But prostaglandin E1 can be dangerous as it can cause apnea. Another example of preliminary treatment is heart catheterization 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 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 three-stage procedure, the right atrium is disconnected from the pulmonary circulation. The systemic venous return goes directly to the lungs, by-passing the heart.

Another treatment option involves the electrosurgical puncture of the atretic valve using a wire introduced into the patient percutaneously. The puncture is then dilated using a balloon catheter to allow blood flow from the right ventricle into the pulmonary artery.^[2]

Prognosis

The outcome varies for every child. If the condition is left uncorrected it may be fatal, but the prognosis has greatly improved over the years for babies with pulmonary atresia. Some factors that affect how well the child does include how well the heart is beating, the condition of the blood vessels that supply the heart, and how leaky the other heart valves are. Most cases of pulmonary atresia can be helped with surgery. If the patient's right ventricle is exceptionally small, many surgeries will be needed in order to help stimulate normal circulation of blood to the heart.

If uncorrected, babies with this type of congenital heart disease may only survive for the first few days of life while the fetal shunts between left and right circulations remain patent. However, there are cases of uncorrected Pulmonary Atresia in which the baby has survived.

Many children with pulmonary atresia will go on to lead 'normal' lives. Patients are usually seen regularly throughout their lifetime by a cardiologist to be sure that their heart is functioning properly. They have an increased risk of endocarditis.

References

External links

• Pulmonary Atresia information from Seattle Children's Hospital Heart Center
• Information from Children's Hospital Boston
• Information from American Heart Association
• from Congenital Heart Surgeons' Society
• Information from Medline Plus
• Information from Texas Heart Institute
• Pulmonary atresia information for parents.