Single ventricle refers to a group of congenital heart defects in which there is functionally only one pumping chamber and a mixing of both oxygenated and deoxygenated blood within the ventricle. Surgical repair involves separating the oxygenated blood from the deoxygenated blood in an operation known as the Fontan repair. The Fontan works by the passive flow of deoxygenated blood through the right side of the heart into the lungs where it picks up oxygen, then returns to the left side of the heart where it is pumped to the rest of the body by the single ventricle. The Fontan is typically a staged operation where most patients are initially treated with a shunt, a Glenn anastomosis, or banding of the pulmonary artery. The Fontan operation corrects cyanosis and eliminates the right to left shunt which is present in patients with a single ventricle.
The Fontan operation has undergone several modifications over the years in an attempt to improve the long term results. The original operation known as an atriopulmonary anastomosis consisted of a connection between the right atrium and the pulmonary artery. Over time, this produced severe enlargement of the right atrium and atrial arrhythmias such as atrial flutter. The surgery was subsequently modified by creating a tunnel within the right atrium to direct blood from the inferior vena cava into the pulmonary artery. This “lateral tunnel” type of Fontan is more efficient and less prone to arrhythmias and the formation of blood clots. In some patients, the Fontan is performed by placing a conduit outside of the heart from the inferior vena cava to the pulmonary artery. Patients who have an atriopulmonary form of Fontan and complications such as arrhythmias and blood clots may be advised to undergo Fontan conversion to the extracardiac form.
While the Fontan operation has improved long term survival in patients with a single ventricle, it has become apparent that there is a deterioration in Fontan function during adulthood. Many years of elevated pressure within the Fontan circuit can result in fluid retention, liver abnormalities, and protein losing enteropathy. While the time course for these events is variable, it has become apparent that these complications increase with the age since Fontan repair. Efforts are underway to determine the best treatment options when these complications arise.