Pulmonary atresia exists as two main categories – pulmonary atresia with intact ventricular septum (PA/IVS) and pulmonary atresia with ventricular septal defect (PA/VSD).
Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)
Children with pulmonary atresia with intact ventricular septum (PA/IVS) are born without a functioning pulmonary valve – the valve located between the heart’s right ventricle (lower right chamber) and the pulmonary artery that leads to the lungs. Instead a non-opening plate of tissue exists where the valve is supposed to be. Without a functioning pulmonary valve, blood cannot flow properly from the heart’s right ventricle to the lungs. The wall between the two lower pumping chambers is completely formed – since there is no hole between the lower pumping chambers, this is referred to as intact ventricular septum. Blood that enters the right ventricle has no way to directly exit the pumping chamber. Since blood cannot exit the right side of the heart, it instead passes through a hole (an atrial septal defect or patent foramen ovale) in the wall that separates the heart’s two upper chambers. The wall is called the atrial septum.
Lack of blood flow to the right ventricle causes the chamber to develop poorly and become small and ineffective as a pump. The tricuspid valve, which lies between the right upper and lower chambers, may also be poorly developed.
As the right atrium empties its oxygen-poor blood through the hole in the heart wall into the left atrium, the bluish blood mixes with red, oxygen-rich blood in the left upper chamber. The resulting mixture of oxygen-poor and oxygen-rich blood is pumped out of the heart through the aorta and to the body. With less oxygen in the blood circulating through his or her body, the baby may appear blue or cyanotic.
In newborn infants, some of the blood leaving the heart via the aorta may go to the lungs through the ductus arteriosus, a vessel that all babies have before birth that carries blood between the aorta and the pulmonary artery but which begins to close within hours or days of birth in most babies. Oxygen-rich blood flowing from the lungs into the circulation is further reduced if the ductus arteriosus closes, resulting in severe cyanosis.
Once the ductus arteriosus begins to close, or if the hole in the wall between the two atria becomes smaller, the child will become quite ill. Immediate medical attention will be required.
Progression and Possible Complications
The child with PA/IVS will develop normally before birth, with oxygen-rich blood flowing through the patent foramen ovale (PFO -- hole in heart wall between the heart’s upper chambers) and the ductus arteriosus. Immediately after birth the child may also do well. However, after birth, the baby may develop an intense bluish discoloration of the skin.
Coronary artery abnormalities including persistent connections from the right ventricle to the coronary arteries (sinusoids) and coronary artery narrowing (stenosis) are sometimes associated with PA/IVS. While this may be suspected from the heart ultrasound, a diagnostic catheterization is often necessary to further define the anatomy prior to any surgical repair. Heart catheterization is a procedure during which a thin, flexible tube called a catheter is fed through an artery to the heart and used to take diagnostic images. The presence of coronary sinusoids may be a risk factor for sudden death.
Initially, babies born with PA/IVS will require a medicine called prostaglandin E1 to keep the ductus arteriosus open. Since the front door (pulmonary valve) is closed, the back door to the lung vessels (ductus arteriosus) must be kept open to allow blood to get to the lungs in order to pick up oxygen.
Even though the right ventricle may be small initially, it may be possible to use this ventricle to supply blood to the lungs. The tricuspid valve and body of the right ventricle need to be of reasonable size. Also, the coronary arteries cannot be “right ventricle dependent,” that is, flow through the coronary arteries cannot depend on the presence of the abnormal communications from the right ventricle to the coronary circulation, which may have areas of narrowing (stenosis). If the coronary artery supply is very abnormal, this may be a very high-risk situation regardless of which intervention is performed. In some situations, a baby with these kinds of coronary abnormalities may be referred for heart transplantation instead.
In certain circumstances, the valve plate may be able to be perforated in the catheterization lab and a balloon dilation catheter may be used to open the valve plate (balloon valvuloplasty). This will allow blood from the right ventricle to pass directly into the lung arteries. For some babies, this may allow enough blood to pass through to the lungs. However, some babies will need additional blood flow to the lungs, at which point a tube will be placed by surgery from one of the arteries directly to the lungs (modified Blalock-Taussig shunt) or the ductus arteriosus may be stented.
As the child grows, the valve area may renarrow and it may be necessary to undergo another valvuloplasty to open the valve further. Some children will need to undergo another operation to make sure that enough blood gets to the lungs.
If the right ventricle and its components are too small, a child may have to go down a “single ventricle” pathway for treatment. This is a staged surgical route ending up with a Fontan repair.
Pulmonary Atresia with Ventricular Septal Defect (PA/VSD)
PA/VSD occurs when there is a hole between the two bottom pumping chambers and there is no direct connection to the lung’s blood vessels. Sometimes the lung vessels are normally formed but just aren’t connected to the heart. However in some situations, the normal lung vessels may be very small or even non-existent. Instead, arterial branches to the lungs (aortopulmonary collaterals) may arise from the main artery leading to the body (the aorta). The abbreviation MAPCA (Multiple Aorto-Pulmonary Collateral Arteries) may be used in this context.
Usually, multiple catheterization procedures are necessary to define the anatomy of these vessels before and after surgery. Multiple staged surgeries may be necessary to try to bring these collateral vessels together to try to attach them together to eventually reconnect them to the heart. As these vessels are abnormal, they may develop narrowings (stenoses) that may require frequent attempts to dilate or stent them in a hospital’s catheterization lab. These narrowings may occur within the vessels or in the areas where the vessels have been reconnected together.
Pulmonary atresia, along with tetralogy of Fallot, interrupted aortic arch and truncus arteriosus may be associated with DiGeorge Syndrome, which is a chromosomal abnormality caused by a missing section (deletion) of the 22nd chromosome. There is a special genetic test that can diagnose this deletion. People with DiGeorge Syndrome may have problems with metabolism of calcium, absent thymus, disorders of immune function, thyroid dysfunction, cleft palate, and learning disabilities.
Initially after birth, an assessment must be made as to how blood is getting to the lungs. In some situations, an echocardiogram will demonstrate good-sized normal pulmonary arteries that are connected together with blood coming from the ductus arteriosus. The blood supply to the lung vessels is ensured by either placement of a tube from one of the body arteries to the lungs (modified Blalock-Taussig shunt) or by placement of a stent in the ductus arteriosus. After the child grows, a more definitive surgical repair is performed at 6 to 12 months of age at which time the hole between the lower chambers of the heart (ventricular septal defect – VSD) is closed with a patch, the shunt is ligated (closed off), and a tube containing a biologic valve is placed from the heart directly to the lung vessels. As the child grows, this tube will require replacement.
If MAPCAs exist, the options are more complicated. If these vessels are suspected, the baby will undergo a diagnostic catheterization shortly after birth in order to map out where these vessels arise and to which part of the lungs they go. Typically, prostaglandin infusions are not necessary, as the ductus arteriosus may not exist. The baby may not need an initial surgery shortly after birth. Instead, staged procedures may be considered starting at 3 to 6 months of age. The purpose is to try to bring these vessels together surgically to re-create the lung vessels so they will eventually be able to be connected back to the heart. These procedures are called unifocalization procedures. This process of rebuilding the lung vessels may require multiple surgical and catheter-based procedures. These vessels may become narrowed, at which time angioplasty, stenting, or further surgical repair may be considered.
Single Ventricle Pathway (Fontan Procedure)
For some children born with congenital heart disease, it is not possible to restore the normal circulation such that the blue (oxygen-poor) blood and red (oxygen-rich) blood sides of the heart are separated with an individual pumping chamber (ventricle) dedicated to each side. These children embark on a different pathway – the single ventricle pathway. In some situations, children are born with one pumping chamber. In others, one chamber may be too small to do its job adequately. Typically, following this pathway requires at least two surgeries before separation of the blue and red circulations is attained. When the circulations are finally separated, blood is only actively pumped from the heart to the body. Blood must pass through the lungs passively. A careful balance of pressures and blood flows is necessary for efficient blood circulation.
Separation of the blue and red blood circulation is achieved through three stages.
- Stage I, restricting and maintaining blood flow to the lungs: After birth, it may be necessary to use an infusion of prostaglandin E1 to keep the ductus arteriosus open, which allows blood to enter the lungs. However, the ductus will shrink away if the prostaglandin infusion is stopped. If the ductus arteriosus is of normal size, too much blood can actually pass through to the lungs, which can result in symptoms of congestive heart failure. Some babies are born with a normal-size pulmonary (lung) artery, which allows blood to go directly to the lungs from the heart despite only having one functional ventricle. Over time, too much blood can pass through to the lungs causing worsening symptoms of congestive heart failure. So a proper balance of blood going to the lungs compared to the rest of the body needs to be achieved. Additionally, having a wide-open connection to the lungs with either a patent ductus arteriosus or pulmonary artery may transmit high pressures to the lung vessels that may damage them over time. So it is important to restrict both excessive blood flow and excessive pressure to the lungs.
If the ductus arteriosus is the main pathway of blood to the lungs, a small tube is inserted between one of the body arteries and the pulmonary artery to enable adequate blood flow to the lungs without the ductus arteriosus. This new tube is called an aorto-pulmonary shunt or modified Blalock-Taussig (B-T) shunt. In some circumstances, the ductus arteriosus can be stented to create a similar situation. If the pulmonary artery is wide open, this restriction is created by surgically placing a tight band around the lung artery (pulmonary artery band) to restrict blood flow and pressure. If a more extensive reconstruction is necessary to guarantee outflow to the body, this procedure is called a Norwood procedure. In addition to making sure that there is no obstruction of blood flow out to the body, the wall between the upper chambers of the heart (atrial septum) is removed so blood won’t back up into the lungs.
- Stage II, starting the separation (bidirectional Glenn and hemi-Fontan procedures): In the past, many patients proceeded directly to a Fontan surgical procedure. However, over time, it was found that dividing the process into two separate surgeries was more successful and better tolerated by the patient.
In the second procedure, performed at about 4 to 6 months of age, the blood vessel that returns blood from the head, neck and arms, called the superior vena cava, is connected directly into the blood vessel going to the lungs (the pulmonary artery). This procedure is called the bi-directional Glenn procedure or hemi-Fontan procedure. The previously placed B-T shunt is removed. It is no longer needed since blood coming back from the upper body now supplies blood to the lungs. This is more efficient because very oxygen-poor blood goes directly to the lungs to pick up oxygen, rather than being diluted with pink blood first. It also allows this blood to avoid going into the heart first where the extra blood volume may cause some strain on the heart. Blood coming back from the lower body is not rerouted at this time and continues to mix with the blood from the lungs. Thus, a bluish discoloration of the child’s skin persists.
- Stage III, Fontan completion: When the child reaches about 18 months to 4 years of age, the third stage of surgery is performed. In this procedure, called the Fontan procedure, the vein (inferior vena cava) carrying blood from the lower body is connected to the pulmonary arteries, thus completing the separation of the blue and red blood circulations. This is performed by constructing a baffle that passes through one of the upper filling chambers (lateral tunnel Fontan) or by attaching the inferior vena cava to a tube that bypasses the heart and attached to the lung vessels (extracardiac conduit Fontan). In either case, typically a small hole is left between the tunnel or conduit to the other side of the upper heart chamber. This is called a fenestration and it acts like a pop-off valve in case the pressure within the non-pumping side of the circulation becomes too high. Methods are being developed to be able to create these results using catheters (thin tubes that are threaded into arteries) and stents (metal, mesh tubes) in the catheterization lab rather than by surgery. After a while, if it is felt that the hole is no longer needed, this hole can be closed in the catheterization lab using catheter-delivered devices to seal the hole.
The “Hybrid Norwood Procedure”
This newer procedure is a “hybrid” effort between the interventional cardiologist and the cardiac surgeon to create the three necessary conditions of a successful first stage:
- Restriction of pulmonary blood flow – the surgeon places small bands on each of the pulmonary arteries to limit the amount of blood flow and pressure to them.
- Unobstructed flow to the body – the cardiologist places a stent within the ductus arteriosus. (In this setting, the ductus needs to be wide open since the blood flow will be going to the body rather than toward the lungs. In some situations, a tube needs to be placed to allow enough blood to go to the head and neck arteries).
3. Unobstructed blood flow from the lungs back to the heart – an opening is created in the wall using special catheters or stents between the upper chambers of the heart (atrial septum) to allow oxygen-rich blood from the lungs to return to the heart without difficulty.
For the Fontan procedure to succeed, the ventricle must be reasonably healthy and able to “suck” blood from the pulmonary circulation in order to propel it forward effectively. If the ventricle is not healthy and strong enough, blood can get backed up into the lungs. The pressure within the veins and lung arteries can rise, which can result in fluid build-up within and outside the lungs. Swelling of the abdomen and extremities also may occur because the blood cannot be effectively circulated through the veins.
Over time, the Fontan circulation, particularly in the setting of an internal tunnel, can increase the risk of stretching the heart’s right atrium. Today’s more refined surgical techniques make this less frequent than in the past. A stretched atrium may cause abnormal heart rhythms, which tends to be poorly tolerated by patients who have had the Fontan procedure.