What is Fontan operation?

What is Fontan operation?

Fontan operation is an operation used for treatment of certain birth defects of the heart like tricuspid atresia. In tricuspid atresia there is no opening for the tricuspid valve. Tricuspid valve is the valve between the right upper and lower chambers of the heart. It guards the opening from the right atrium to the right ventricle and prevents backflow of blood when the right ventricle contracts. When there is tricuspid atresia, blood reaches the left atrium through a defect in the wall between the two, which is mandatory for survival in such cases.

From the left atrium blood reaches the left ventricle. So blood flow to the lungs for oxygenation needs another associated defect like a defect in the wall between the two ventricles or a communication between the aorta and pulmonary artery. Pulmonary artery is the blood vessel to the lungs from the right ventricle. Aorta is the major blood vessel arising from the left ventricle, carrying oxygenated blood to the whole body.

Fontan operation was described by Francis Fontan in 1960. Blood returning from the lower part of the body through inferior vena cava is directed to the left lung by this operation. Blood coming from the upper part of the body through the superior vena cava is directed to the right lung. For this operation to be successful, the size of the pulmonary arteries must be large and the pressure in them low to permit blood flow. This is because there is no muscular chamber like the right ventricle in the Fontan circuit to pump blood into the lungs. Blood should flow passively into the lungs.

Various modifications of Fontan procedure have been used since the initial description in 1960 to improve the long term results. An important modification is called total cavopulmonary connection, described by Marc de Leval in 1988. Artificial grafts are used in this procedure to direct blood to the pulmonary arteries, along with part of the right atrium. Other variations of the procedure may use a tube outside the heart to achieve the same effect. Fontan procedure is also used for other types of birth defects of the heart in which only one ventricle can function well due to the defects. Functional ventricle is used to pump blood to the aorta and Fontan circuit to take blood to the lungs.

Long term follow up after Fontan operation has been published from Mayo Clinic. They reviewed the outcome of all patients who had undergone modified Fontan operation between 1973 and 2012. 10 year survival for the 1052 patients in the database was 74%. 20 year survival was 61% and 30 year survival 43%. Survival was better if the heart rhythm was normal after the surgery.  Most common reasons for reoperations were pacemaker insertion, Fontan circuit revision and the need for replacing the valves between the ventricles. Pacemaker is a device used to give regular electrical signals to the heart when heart’s own intrinsic rate is low due to some reason.

An important long term complication after Fontan surgery is late development of heart rhythm abnormalities which can occur in nearly half of them. A rare complication is protein losing enteropathy in which protein is lost from the intestine. Another rare problem in the lungs is called plastic bronchitis. Fontan patients also have a higher chance of clot formation and migration leading to blockage of blood vessels elsewhere. Though there are long term complications for the Fontan procedure, it should be remembered that without the procedure, the survival of those patients will be very low.

Twenty year survival of 84% after modified Fontan procedure has been reported in another series of 305 patients operated between 1980 and 2000. They noted better survival with improved techniques. 15 year survival was 81% after one type of modification versus 94% for another modification. Fontan circulation is basically a single ventricle heart with the dominant ventricle supporting blood circulation to the whole body and passive blood flow into the lungs through a connection from the great veins to the lungs.