Single Ventricle Defects and the Fontan Procedure

The heart has two sides: a left side and a right side. Within these sides lie the chambers of the heart – there are two pumping chambers (the ventricles) and two collecting chambers.

In a normally-developed heart, the oxygen-poor (blue) blood returns to the right atrium from the body, enters the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. The oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle and is then pumped out to the body through the aorta.

For children with single ventricle defects, one of the ventricles has not developed properly or the inside arrangement of the two ventricles is too complicated to be separated into two.

The red blood will then mix with the blue blood, causing cyanosis or blueness, because the body receives less oxygenated blood. In order to thrive, babies born with single ventricle defects will need surgical intervention.

There are six types of single ventricle defects:

1. Hypoplastic left heart syndrome (HLHS): HLHS is a combination of several abnormalities of the heart and great blood vessels. Most structures on the left side of the heart are small and underdeveloped with this condition.
2. Tricuspid atresia: In tricuspid atresia, the tricuspid valve, normally located between the right atrium and the right ventricle, does not develop properly during pregnancy and remains completely obstructed.
3. Double outlet right ventricle: The pulmonary artery and aorta come out of the right ventricle. Sometimes the left ventricle remains small or it’s impossible to channel the blood from the left ventricle into the aorta.
4. Double inlet left ventricle: The two collecting chambers connect to the left ventricle resulting in the right ventricle being underdeveloped.
5. Unbalanced atrioventricular septal defect (AVSD): There is a large opening between the collecting and pumping chambers of the heart with abnormal valves. One of the pumping chambers remains smaller than the other.
6. Pulmonary atresia and intact ventricular septum: The exit of the right ventricle is obstructed and it remains very muscular and small.

It is generally unknown what causes single ventricle defects. In some cases it may have a genetic link, in others, it may occur randomly.

Single ventricle defects are rare, occurring in about five out of every 100,000 live births.

Single ventricle defects can be diagnosed while your baby is still in utero. These issues are not always caught in utero, though. Regardless of when diagnosis occurs, in most cases your baby will have to undergo surgery immediately after being born or within the first few days of life to correct the single ventricle defect.

The Fontan procedure is the last in a series of operations that tries to establish a near-normal circulation of blood. In the Fontan procedure, the veins draining the blood from the body are connected directly to the lung arteries, thereby bypassing the heart.

There are three surgeries, or stages, to treat single ventricle defects. These stages adjust the blood flow to the lungs in order to maintain oxygenation, preserve lung integrity and prepare the body for the Fontan circulation. Doing three surgeries lessens strain on the heart that can occur from the changes in functionality that happen in each procedure:

• First stage: This stage happens within the first few days of life: a shunt, pulmonary artery banding or Norwood procedure is performed to regulate the pulmonary blood flow. The shunt lets more blood go to the lungs. The pulmonary artery band prevents too much blood from circulating in the lungs. The Norwood procedure combines a shunt and a complex intervention to the major blood vessels leading to the heart. Not all children will have this first surgical stage.
• Second stage: Known as the Glenn procedure, this second surgery replaces the first shunt (if there was one) in late infancy and consists of connecting the superior vena cava (the vein draining the blood from the upper part of the body) to the lung arteries. While more red blood will get to the body, some mixing of red and blue blood will still occur.
• Third stage, or Fontan: In the Fontan procedure, the blood flow is taken from the inferior vena cava (the vein draining the blood from the lower part of the body) and gets plugged into the pulmonary artery. The single ventricle will pump blood returning from the lungs to the body. The blood returning from the body will not be pumped to the lungs by the heart but will flow passively from the body to the lungs by the direct blood vessel connections from the lower and upper body to the lung arteries. This will allow complete separation of the blue and red blood, improving oxygenation. Children usually have the Fontan procedure around 3 years old.

Your physician will discuss risks with you and your family in greater detail. Potential risks of the Fontan procedure may include:

• Liver dysfunction
• Kidney issues
• Pregnancy complications, including blood clots and arrhythmia
• Some patients may need additional catheterization procedures, pacemakers or other surgeries over time.

Yes, long-term follow-up care is needed for children who have the Fontan procedure. Your child would continue to see a pediatric cardiologist throughout childhood and adolescence, and would transition to adult care at the end of adolescence. Your cardiologist will monitor your child’s heart and the Fontan procedure itself, as well as liver and kidney function.