Pulmonary Atresia (PA)
 

Definition         What is pulmonary atresia?
The heart has two pumping chambers (right and left ventricles). Each ventricle pumps blood through a valve to an artery. The right ventricle pumps blood to the lungs through the pulmonary artery. At the origin of the pulmonary artery there is a valve which allow blood flow in one direction and prevent it from going backwards, this is termed the pulmonary valve. Abnormal development of the pulmonary valve may lead to its inability to open thus obstructing blood flow. Since blood can not cross the pulmonary valve it will cross the communication normally present between the right and left atria, thus bypassing the right ventricle. Lack of blood flow to the right ventricle will cause it to develop poorly and become small and ineffective as a pumping chamber.

The pulmonary valve does not open (atretic) and the right ventricle (RV) is small.  There is an atrial septal defect (ASD).
 

Incidence        How common or rare is this disease?
This is the 10th most common congenital heart disease amongst neonates. It is the 23rd most common congenital heart disease. It occurs in 0.07 per 1,000 live births.
 

Effects         What does it cause?
The blood returning from the body, which happens to be poorly oxygenated (blue in color) can not travel its normal path since the pulmonary valve is obstructive, and the right ventricle is consequently underdeveloped. Therefore, the right atrium will empty its blood into the left atrium through a communication (patent foramen ovale or atrial septal defect) to mix with the blood returning from the lungs. This will cause discoloration of the well oxygenated blood returning from the lungs leading to bluish discoloration of the skin (cyanosis). The blood (from right and left atria) will then go the left ventricle which would pump blood to the aorta. In the aorta blood will provide blood supply to the body and in addition blood will go to the lungs through a blood vessel present in all unborn children and lasts for hours or months after birth known as the ductus arteriosus. Once the ductus arteriosus starts closing or the communication between the two atria become smaller then the child will become quite ill requiring immediate medical attention.

Blood returning from the body (blue) can not cross the pulmonary valve, therefore, crosses over to the left atrium at the atrial septal defect (ASD), causing the blood in the left heart to become purple in color (cyanosis).
 

Course         How would this disease progress?
The child will develop normally before birth because of the presence of the patent foramen ovale and the ductus arteriosus, after birth the child will initially do well, however, within few hours the child may deteriorate because of decrease blood flow to the lungs manifesting as intense bluish discoloration of the skin.
 

Treatment         Does it require any treatment?
Rashkind atrial septostomy

Occasionally, the atrial communication (patent foramen ovale or PFO) is too small and require enlargement.  This could be done by a procedure termed Rashkind atrial septostomy.  In this procedure a catheter with an inflatable balloon at it s end enters the right atrium and crosses the atrial communication into the left atrium.   In the left atrium the balloon is inflated and the catheter is pulled back briskly into the right atrium causing a tear in the atrial septum, thus enlarging the atrial communication.
Untreated, children with this heart disease will eventually die. Surgical repair is available, however, unlike many other heart lesions the goal is not to duplicate the anatomy and physiology of a normal heart, instead the goal is to separate the blue and pink circulations of the blood to secure better oxygen delivery to the body and relieve the burden of extra load on the heart. This is achieved through three surgical procedures. The first is done soon after birth, in which a communicating blood vessel is inserted between the aorta and the pulmonary artery to enable adequate blood flow to the lungs (this communicating blood vessel is termed systemic to pulmonary arterial shunt or Blalock-Taussig shunt (B-T shunt) as the ductus arteriosus become progressively smaller. In the second procedure the blood vessel returning blood from the head, neck and arms (called superior vena cava) is connected directly into the blood vessel going to the lungs (pulmonary arteries), this procedure is labeled bi-directional Glenn procedure. In this second surgery the previously placed B-T shunt is removed as it will not be needed anymore since the blood coming back from the upper part of the body will provide blood supply to the lungs through the bi-directional Glenn. After the second surgery the blood coming back from the lower part of the body continue to mix with the blood from the lungs, therefore, bluish discoloration of the child’s skin persists.

The PDA is tied (ligated) and replaced by a more reliable source of blood flow (systemic to pulmonary arterial (S-P), also called B-T shunt).

 

 
The third surgery is performed at about 18 months of age. In this procedure the vein carrying blood from the lower part of the body (inferior vena cava is connected to the pulmonary arteries, thus separating the blue and pink blood circulations. This surgical procedure is termed the Fontan procedure. Hearts with the Fontan procedure have only one functioning pumping chamber (ventricle), which pumps blood to the body. Blood to the lungs go directly from the veins returning blue (poorly oxygenated) blood from the body into the lungs without a ventricle. This is made possible by sump like effect the single ventricle has which would "suck" blood from the lung circulation enabling the blood to cross the pulmonary circulation and into the ventricle.

The B-T shunt is then replaced by the Glenn shunt (connecting the superior vena cava (SVC) to the pulmonary arterial system.

The blood from the inferior vena cava (IVC) is then directed towards the pulmonary arterial vessels through the Fontan connection.
Occasionally, the right ventricle may develop normally if there is a hole communicating it with the left ventricle (ventricular septal defect or VSD). The presence of such a defect will allow the blood to cross the tricuspid valve and into the right ventricle, then escape into the left ventricle through the communicating hole (VSD). In these circumstances a Rashkind atrial septostomy is not necessary. In addition, instead of a Fontan procedure, the right ventricle could be connected to the pulmonary arteries using a pulmonary artery from a diseased child, and closing the VSD with the patch.

If the right ventricle is of an adequate size then a "biventricular repair" could be performed.  In this surgery a conduit connects the RV to the pulmonary arteries and the ventricular septal defect (if present) is closed with a patch.
 

Complications
The Fontan procedure to succeed require that the single ventricle to be reasonably healthy and able to suck blood from the pulmonary circulation and propel blood forward effectively, otherwise the procedure will fail. This is manifested as swelling of the body since blood can not be effectively moved into the pulmonary circulation. Also, there are risks of stretching the right atrium, although this is less frequently nowadays with more refined surgical techniques, and this may cause abnormal heart rhythm which tends to be poorly tolerated by patients with the Fontan procedure.