Diagnosis of Single Ventricle Anomalies
In most cases an echocardiogram will be able to define the details of the cardiac anatomy for the initial diagnosis in the newborn period. Echocardiography will also be important in following the anatomy and function of the various components of the cardiovascular system, such as valve or ventricular function, as the child grows.
Cardiac catheterization is only occasionally necessary in a newborn with a single ventricle anomaly, if there are details of the anatomy that cannot be determined by echocardiogram. However, patients with single ventricle anomalies will have a cardiac catheterization prior to the second surgery (Glenn shunt) and again before the third surgery (Fontan procedure). These cardiac catheterizations are done to look at the anatomy, particularly of the pulmonary arteries, and to obtain pressure measurements in the heart. These pressure measurements are important in determining if a patient with a single ventricle anomaly is a good candidate for surgery.
Catheter interventions such as dilation or stenting of pulmonary arteries or coil occlusion of abnormal collateral (extra) vessels may be performed at the time of these cardiac catheterizations.
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.
The "Fontan circulation" refers to this 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.
Good Candidates for Fontan Surgery
For a heart with a Fontan reconstruction to work well, there are a few crucial features that must be maintained. These key factors must be kept in mind when planning the medical or surgical management of children with single ventricle defects from the first day of life onward.
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.
Lastly, leaky or tight valves may adversely 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 is quite varied depending on the specific type of single ventricle cardiac defect. In some babies there is not enough blood flow into the lungs, resulting in cyanosis. In these babies, a tube graft is placed from an artery (usually the left subclavian or left innominate artery) to the pulmonary artery. This is called a systemic to pulmonary artery shunt or Blalock-Taussig (BT) shunt.
In other babies, the flow of blood into the lungs may be too much, placing an extra burden on the ventricle and exposing the pulmonary arteries to dangerously high pressure. In these babies, a procedure will be performed 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 require more complex operations, such as the Norwood procedure for patients with hypoplastic left heart syndrome.
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.
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.
The second stage for most children with single ventricle anomalies 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 has two major advantages in most children. First, because the connection is a direct one between two blood vessels, rather than made of artificial matter, it has the ability to grow with the child.
Second, it 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). 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 placed inside the atrium so that blood returning from the inferior vena cava is directed through this tunnel. A connection is then 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 synthetic tube, usually Gore-Tex, and is sewn to the underside of the pulmonary artery, routing this blue blood flow outside of the heart.
In either method, a hole, or "fenestration," is often made between the Fontan circuit and the right atrium 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 with smaller and less prolonged collections of fluid within the chest (a common complication after Fontan surgery). Many fenestrations close spontaneously many months after surgery, but can also be closed during a cardiac catheterization procedure if deemed necessary.
Currently, 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 achieved its maximal efficiency in terms of ventricular work and near normal oxygen levels, but its capacity for work will usually not match that of a normal heart when examined using sophisticated testing.
The limitations children experience due to their heart defect, though, 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.
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 in their early 30s, 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 anomaly, continued regular follow-up with a cardiologist for the life of a patient is essential.
Adult and Adolescent Management
A patient with a single ventricle anomaly has only one pumping chamber. All adult patients with such a history require lifelong excellent and expert congenital heart surveillance.
Single ventricle patients may reach adult life in two ways.
The first is that they are still blue or cyanotic. Such patients will definitely have problems and will require lifelong expert surveillance 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, and Fontan patients need careful and thoughtful surveillance throughout their lives by experts in complex congenital heart disease. Many Fontan patients will have abnormal heart rhythms that require treatment. Some will have low oxygen levels in their blood that may limit their physical abilities, and that may require the blockage of abnormal vessels that were allowing blue blood to mix with red blood. Some Fontan patients may have weakening of their pumping chamber or leakage of one or more valves. Perhaps 10 percent of these patients may develop an unusual condition called “protein losing enteropathy.” This requires very careful management. Fontan patients may also develop problems with liver or kidney function, so 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 definitely receive counseling and assessment before becoming pregnant, and should have their pregnancy managed by a special maternal fetal medicine team skilled at managing pregnancy in women with other health conditions.
Learn more about the Adolescent and Adult Congenital Heart Disease Program.