The term “single ventricle anomaly” is purposely non-specific. It is used to describe a group of cardiac defects that may differ quite dramatically from each other but share the common feature that only one of the two ventricles is of adequate functional size.
Some of the anomalies described as single ventricle defects include:
- Tricuspid atresia
- Hypoplastic left heart syndrome
- Double inlet left ventricle
- Many of the heterotaxy defects
- Some variations of double outlet right ventricle
The ultimate plan for reconstruction is actually quite similar for most of these anomalies. All will generally undergo staged reconstructive procedures ultimately resulting in a Fontan circulation.
In the normal heart each ventricle does a separate job. The right ventricle pumps blood to the lungs, and the left ventricle pumps blood to the body. In a single ventricle heart, there is only one ventricle large enough to do the normal job of pumping blood.
Whenever there is only one ventricle large enough to do a normal job of pumping blood, we need to configure the circulation to maximize the efficiency of this single ventricle without overworking it. This ultimately requires committing the single ventricle to doing the harder work of the heart, pumping blood to the body. The job of getting blood to the lungs must be done without a pump.
How long a heart with a single ventricle reconstruction can function is not known. The first children to have a successful Fontan operation are just now 30 years old and many improvements in surgical technique and medical management have occurred over this time period.
Late complications including irregular rhythms and heart failure may occur. Some speculate that most single ventricle hearts will not function efficiently beyond 30 to 40 years, but improvements in surgical technique and medical care may increase this age significantly. In some cases, if the ventricular function deteriorates significantly, heart transplantation may be considered. Because of the possibility of late complications in patients with single ventricle anamoly, continued regular follow-up with a cardiologist for the life of a patient is essential.
The “Fontan circulation” refers to the configuration where the single ventricle pumps blood returning from the lungs to the body, and the blood returning from the body travels to the lungs by direct blood vessel connections without a pumping chamber. In any individual child there may be different procedures needed to achieve this goal.
For a heart with a Fontan reconstruction to work well, there are a few crucial features that must be maintained:
- The single ventricle must not be overworked for a long period of time, in terms of either having to pump too much blood or pump at too high a pressure.
- The pulmonary arteries must grow well without stenosis (narrowing) and must remain low resistance (or be very relaxed). If the pulmonary arteries are narrow or if the resistance in these vessels is high, blood will not be able to flow into them without a pump, so the Fontan will not be successful.
- Leaky or tight valves may adversely affect the function of the ventricle or the flow of blood to the lungs.
The type of operation needed in the newborn period is quite varied depending on the specific type of single ventricle cardiac defect. Whatever is needed in the newborn period, the aim is typically to balance the blood flow between the lungs and the body, achieving stable oxygen levels and adequate heart function. Some of the operations performed at this stage include:
- Systemic to pulmonary artery shunt or Blalock-Taussig (BT) shunt
- A procedure to restrict blood flow to the lungs
- The Norwood procedure
Rarely, a baby with a single ventricle anomaly will have “just right” flow into the lungs so that an equal amount of blood flows to the body and the lungs. These babies do not require intervention in the newborn period.
The second stage for most children with single ventricle anomolies is undertaken around three to six months of age. The operation is called a “bi-directional Glenn” or sometimes a “hemi-Fontan”. During the Glenn operation the large vessel that drains blood from the head and upper body back to the heart (the superior vena cava) is taken off the heart and sewn directly to the pulmonary artery. If a prior BT shunt was present, it is removed. If a pulmonary artery band was previously placed, it may be removed but can also be left in place in some situations.
The Glenn operation removes some of the work from the single ventricle so that the ventricle will no longer have to pump all of the blood to the lungs in addition to all of the blood to the body. This replaces the risk for early heart failure. In most cases this stage is tolerated the best of all the stages with a survival rate of 95 percent or better. After the Glenn operation most children will have oxygen saturation levels of 75 percent to 85 percent.
The third and final stage in the reconstruction of a single ventricle heart defect is the Fontan completion operation. This operation is usually performed at 2 or 3 years of age, based on the child’s size and clinical status.
During the Fontan operation, the blood vessels returning blood to the heart from the lower half of the body (inferior vena cava) is connected directly to the pulmonary arteries. Until now this blood has bypassed the lungs and has been pumped directly to the body resulting in oxygen levels lower than normal. After a Fontan operation, oxygen levels will be nearly normal (90s).
Currently, when patients have been well prepared for Fontan completion, the success rates are 90 percent and higher.
After a successful Fontan surgery, the limitations children experience due to their heart defect can vary greatly. At one end of the spectrum there are children with Fontan circulations who have participated in competitive sports such as swimming and gymnastics. Other children may have significant limitation in their capacity for exercise. Most children fall somewhere in between the extremes.
Most children are on a blood thinner called coumadin after their Fontan to prevent clots from forming in the Fontan circuit. When a child is on a blood thinner, you must take extra careful to avoid falls or head trauma as they are at increased risk for internal bleeding.