Definition and Overview
The Fontan procedure is an operation used to convert the blood flow to an effective single ventricle circulation. It is typically the last operation in a series of surgeries performed in the management of patients with single ventricle physiologies.
Who Should Undergo and Expected Results
The Fontan procedure is used to address single ventricle malformations, which are congenital heart conditions wherein only one ventricle carries out the functions of both – it supports and pumps blood to both the systemic and the pulmonary circulations. There are several abnormalities that produce the single ventricle physiology. In most cases, there is only one functional ventricle while the other is a rudimentary chamber. These include patients with a Double Inlet Ventricle and problems with the atrioventricular valves, among others.
The most commonly encountered kind of single ventricle malformation is tricuspid atresia, which accounts for 1 to 3% of congenital heart diseases. This condition refers to the absence of the tricuspid valve, which supposedly connects the right atrium to the right ventricle. The hypoplastic left heart syndrome, or HLHS, is another spectrum of anomalies that, in effect, results in a single ventricle physiology. In contrast to tricuspid atresia, where the right ventricle is non-functional, HLHS is a condition wherein the left side is underdeveloped.
In both of these conditions, a shunt exists that allows blood from one side of the heart to flow to the other side. Patients typically present with cyanosis or a bluish discoloration of the skin, indicating the lack of oxygenation in the body. Some patients may also present with symptoms of heart failure.
Although the management of these two conditions is not the same, both will eventually have to undergo the Fontan procedure as the final operation.
Many issues remain controversial regarding the optimal timing, the need for staged operations, and the surgical technique for performing a Fontan procedure. In the past, a patient had to be at least four years old to be considered a candidate for the Fontan procedure; nowadays, the age has progressively been lowered, with some patients below two years old already subjected to the procedure.
How is the Procedure Performed?
The primary aim of the Fontan procedure is to completely separate the pulmonary from the systemic circulation and place them in series. In most cases, a previous operation has already been performed to redirect blood flow coming from the superior vena cava (SVC) to the pulmonary bed (bidirectional Glenn shunt or hemi-Fontan operation). The Fontan procedure completes the cavopulmonary connection by attaching the inferior vena cava (IVC) to the pulmonary system.
There are basically two techniques used in performing the Fontan procedure: the lateral tunnel Fontan and the extracardiac Fontan.
In the lateral tunnel Fontan, the connection between the inferior vena cava and the pulmonary circulation passes through the right atrium. The right atrium is opened, and a graft made of polytetrafluoroethylene (PTFE) is sutured around the opening of the IVC, through a part of the atrial septum, to the opening of the previously transected SVC. The previously transected SVC is then attached to the right pulmonary artery, to complete the connection.
On the other hand, the extracardiac Fontan is placed completely outside the heart. The IVC is divided and sutured to one end of the PTFE graft. The other end of the graft is sutured to the right pulmonary artery. In contrast to the lateral tunnel Fontan, wherein the right atrium is integrated into the conduit, the conduit in the extracardiac Fontan is made entirely of PTFE.
Proponents of the extracardiac Fontan argue that one of the main advantages of this technique is the decreased rate of rhythm abnormalities after the procedure since there are no sutures placed in the atrium. Meanwhile, disadvantages have also been pointed out with this technique, which include a higher risk for graft thrombosis, and lack of potential for the graft to grow as the patient grows.
Possible Risks and Complications
The Fontan procedure is fraught with risks and complications, more so in the long-term than in the perioperative period. Mortality has been reduced considerably in recent years, with operative mortality rates now down to approximately 5%. Early complications that can occur soon after surgery include pleural effusions and venous obstructions.
A number of other complications can be encountered in the long-term. The development of collateral vessels has been reported, which could lead to the shunting of blood and consequent hypoxemia or decreased oxygenation. Other complications include problems associated with protein loss, obstruction of the conduit, and heart failure.
Although the Fontan procedure has successfully improved the survival of patients with single ventricles, with reports of survival rates of 73% in 15 years, experts have noted a gradual decline in cardiac function in the long-term, even if the operation was performed under the most ideal conditions. The exact reason and mechanism of this late attrition remain unknown but have been attributed to a combination of factors and late complications, such as constant elevation of venous pressures. Some cases, particularly infants with HLHS, may be considered candidates for heart transplantation later on.
Mahle WT, Wernovsky G, Bridges ND, et al. Impact of early ventricular unloading on exercise performance in preadolescentswith single ventricle Fontan physiology. J Am Coll Cardiol. 1999 Nov 1. 34(5):1637-43.
Choussat A, Fontan F, Besse P. Selection Criteria for the Fontan procedure. In: Anderson RH, Shinebourne EA, eds. Paediatric Cardiology. Edinburgh: Churchill Livingstone;. 1977: 559-66.