What Are Single Ventricle Anomalies and Fontan Circulation?
The term "single ventricle anomaly" is not specific on purpose. This term means a group of cardiac defects that may be different from each other but share the common feature. One of the two ventricles is of good functional size.
Because of this , the plan for reconstruction is similar for most of these defects. All will go through staged reconstructive procedures resulting in a "Fontan circulation."
Some of the abnormalities of single ventricle defects include:
- Tricuspid atresia
- Hypoplastic left heart syndrome
- Double inlet left ventricle a defect that affects the valves and chambers of the heart
- Many of the heterotaxy defects- abnormal position of the heart and or blood vessels
- Some variations of double outlet right ventricle- the main artery that carries blood from the heart to the body and the artery that directs blood from the heart to the lungs is partially or completely blocked.
Diagnosis of Single Ventricle Anomalies
An echocardiogram will help figure out what cardiac defect is present. Echocardiograms are used throughout the patient’s lifetime to watch the defect.
Cardiac catheterization is only needed in a newborn with a single ventricle abnormality, if there are things in the anatomy that cannot be seen by echocardiogram. Computed tomography (CT) scans may be used to to find details that are not able to be completely seen by the echocardiogram. They may be used to give additional information for surgical planning. Patients with single ventricle anomalies will have a cardiac catheterization before the second surgery (Glenn shunt). They will have another before the third surgery (Fontan procedure).
These cardiac catheterizations are done to look at the anatomy, and to get pressure measurements in the heart. These pressure measurements are important in deciding if surgery is a good option for a patient with a single ventricle anomaly.
In the normal heart each ventricle does a separate job. The right ventricle pumps blood to the lungs. 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 change the circulation to make it the best it can be without overworking it.
This needs the single ventricle to pump blood to the body. The job of getting blood to the lungs must be done without a pump.
The "Fontan circulation" refers to this configuration where the single ventricle pumps blood returning from the lungs to the body. The blood returning from the body travels to the lungs by blood vessel connections without a pumping chamber. There may be different surgeries needed.
Good Candidates for Fontan Surgery
For a heart with a Fontan reconstruction to work well, there are a few features that must be maintained.
The single ventricle must continue to work well. It cannot develop dysfunction (poor squeeze or pumping) because of pumping extra volume or pressure. Your child’s cardiologist will watch the function of their heart with echocardiograms. If the function starts to fall, they may start medicines or order more testing.
The pulmonary arteries must grow well without stenosis (narrowing). They 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. This means the Fontan will not be successful.
Leaky or tight valves may negatively affect the function of the ventricle or the flow of blood to the lungs.
Achieving Fontan Circulation
The type of operation needed in the newborn period depends on the specific type of single ventricle cardiac defect. In some babies there is not enough blood flow into the lungs. This leads to cyanosis. In these babies, a tube graft is placed from another artery to the pulmonary artery. This is called a systemic to pulmonary artery shunt. It may be called a Blalock-Taussig (BT) shunt. This can sometimes be done non-invasively in the cardiac catheterization lab with a ductal (PDA) stent.
In other babies, the flow of blood into the lungs may be too much. This puts more work on the ventricle. This may lead to very high pressure in the pulmonary arteries. In these babies, a procedure will be done to restrict blood flow to the lungs. This is done by placing a piece of material or a "band" around the pulmonary artery to narrow it.
Other newborns have more complex heart disease and need more complex operations. This may include the Norwood procedure for patients with hypoplastic left heart syndrome.
Rarely, a baby with a single ventricle defect will have "just right" flow into the lungs. This means that equal amount of blood flows to the body and the lungs. These babies do not need intervention in the newborn period.
The goal for any baby in the newborn period is to balance the blood flow between the lungs and the body. This leads to stable oxygen levels and good heart function.
The second stage for most children with single ventricle defects is done 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. It is sewn on 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. It can also be left in place.
The Glenn operation has two major advantages in most children. First, the connection is a direct one between two blood vessels, rather than made of artificial matter, it can grow with the child.
Second, it removes some of the work from the single ventricle. This means the ventricle will no longer have to pump all the blood to the lungs and all 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. The survival rate is 95 percent or better.
After the Glenn surgery 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 surgery. This surgery is usually done at 2 or 3 years of age.
During the Fontan surgery, the blood vessels returning blood to the heart from the lower half of the body (inferior vena cava) are connected directly to the pulmonary arteries. Until now this blood has avoided the lungs. It has been pumped directly to the body leading to oxygen levels lower than normal.
After a Fontan surgery, oxygen levels will be normal (90s). The two most common methods of performing the Fontan completion today are the "lateral tunnel" and the "extra-cardiac" techniques.
In the lateral tunnel method, a tunnel-like patch is put inside the atrium. Blood returning from the inferior vena cava is sent through this tunnel. A connection is made between the end of the tunnel / top of the right atrium and the underside of the pulmonary artery.
In the extra-cardiac method, the inferior vena cava is connected to a artificial tube. It is sewn to the underside of the pulmonary artery. This sends the blue blood flow outside of the heart.
In either method, a hole or "fenestration" may be made between the Fontan circuit and the right atrium. This is there so that if pressures become very high in the Fontan circuit, there is a "pop-off" into the heart. Patients with fenestrations may have a more stable post-operative course. Many fenestrations close on their own many months after surgery. They can also be closed during a cardiac catheterization procedure if needed.
When patients have been well prepared for Fontan completion, the success rates are 90 percent and higher.
Comparison of Surgery and Two Ventricle Heart
After a successful Fontan surgery, the reconstructed single ventricle heart has gotten to the best that it can. It’s ability to work is different from a normal heart.
The limitations children have due to their heart defect, though, can be very different. Some children with Fontan circulations have played in competitive sports such as swimming and gymnastics.
Other children may have more limits in their ability to exercise. Most children fall somewhere between the extremes.
Most children are on a blood thinner (usually aspirin but sometimes other medications are used) after their Fontan. This stops clots from forming in the Fontan circuit.
How long a heart with a single ventricle reconstruction can function is not known. The first children to have a successful Fontan operation are now 40 years old. Many improvements in surgical technique and medical management have happened.
Late complications including irregular rhythms and heart failure may occur. Some think that most single ventricle hearts will not work well after 30 to 40 years. Improvements in surgical technique and medical care may increase this age significantly. In some cases, if the ventricular function declines significantly, heart transplantation may be considered.
Continued regular follow-up with a cardiologist for the life of a patient is important.
Adult and Adolescent Management
A patient with a single ventricle defect has only one pumping chamber. All adult patients with such a history need lifelong congenital heart monitoring.
Single ventricle patients may reach adult life in two ways.
The first is that they are still blue or cyanotic. Such patients will have problems. They will need lifelong monitoring and management.
The second group has had a Fontan procedure. This procedure made them pink, but they have only one pumping chamber in their heart. As they age, many problems can occur. Fontan patients need careful monitoring throughout their lives by experts in complex congenital heart disease. Many Fontan patients will have abnormal heart rhythms that need treatment. Some will have low oxygen levels in their blood that may limit their physical abilities. Some Fontan patients may have weakening of their pumping chamber or leakage of one or more valves. Ten percent of these patients may have an unusual condition called “protein losing enteropathy.” This needs careful management. Fontan patients may also have problems with liver or kidney function. This needs to be monitored as well.
Most women with a congenital heart disease history may be able to successfully carry one or more pregnancies. Women with complex forms of congenital heart disease should get counseling and assessment before becoming pregnant. They should have their pregnancy managed by a special maternal fetal medicine team.