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The Fontan procedure, or Fontan/Kreutzer procedure, is a palliative surgical procedure used in children with complex congenital heart defects. It involves diverting the venous blood from the right atrium to the pulmonary arteries without passing through the morphologic right ventricle. It was initially described in 1971 by Dr Fontan and Dr Kreutzer separately as a surgical treatment for tricuspid atresia. 
The Fontan procedure has more recently been used in pediatric situations where an infant only has a single effective ventricle, either due to a heart valve defect (e.g. tricuspid or pulmonary atresia), an abnormality of the pumping ability of the heart (e.g. hypoplastic left heart syndrome or hypoplastic right heart syndrome), or a complex congenital heart disease where a bi-ventricular repair is impossible or inadvisable.
Children with hypoplastic left heart syndrome have a single effective ventricle supplying blood to the lungs and the body (either from birth or after an initial surgery e.g. Norwood procedure). They are delicately balanced between inadequate blood supply to the lungs (causing cyanosis) and oversupply to the lungs (causing heart failure). In addition, the single ventricle is doing nearly twice the expected amount of work because it has to pump blood for both lungs and body. As a result, these children can have trouble gaining weight and are also vulnerable to decompensation in the face of otherwise minor illnesses (even a common cold). Sometimes medications (e.g. diuretics) can help them through this stage.
Therefore, when either they are large enough, and if the pressure in the pulmonary arteries is low enough, these children are referred for the Fontan procedure commonly after 2 years of life.
After Fontan, blood must flow through the lungs without being pumped by the heart. Therefore children with high pulmonary vascular resistance may not tolerate a Fontan procedure. Often, cardiac catheterization is performed to check the resistance before proceeding with the surgery. This is also the reason a Fontan procedure cannot be done immediately after birth; the pulmonary vascular resistance is high in utero and takes months to drop.
There are three different types of Fontan procedure:
The Fontan is usually done as a two staged repair.
The first stage, also called a Bidirectional Glenn procedure or Hemi-Fontan (see also Kawashima procedure), involves redirecting oxygen-poor blood from the top of the body to the lungs. That is, the pulmonary arteries are disconnected from their existing blood supply (e.g. a shunt created during a Norwood procedure, a patent ductus arteriosus, etc.). The superior vena cava (SVC), which carries blood returning from the upper body, is disconnected from the heart and instead redirected into the pulmonary arteries. The inferior vena cava (IVC), which carries blood returning from the lower body, continues to connect to the heart.
At this point, patients are no longer in that delicate balance, and the single ventricle is doing much less work. They usually can grow adequately and are less fragile. However, they still have marked hypoxia (because of the IVC blood that is not fed into the lungs to be oxygenated). Therefore, most patients are referred for another surgery.
The second stage, also called Fontan completion, involves redirecting the blood from the IVC to the lungs as well. At this point, the oxygen-poor blood from upper and lower body flows through the lungs without being pumped (driven only by the pressure that builds up in the veins). This corrects the hypoxia and leaves the single ventricle responsible only for supplying blood to the body.
In the short term, children can have trouble with pleural effusions, fluid building up around the lungs. This can require a longer stay in the hospital for drainage with chest tubes. To address this risk, some surgeons make a fenestration from the venous circulation into the atrium. When the pressure in the veins is high, some of the oxygen-poor blood can escape through the fenestration to relieve the pressure. However, this results in hypoxia, so the fenestration may eventually need to be closed by an interventional cardiologist.
In the long term, children can have trouble with atrial flutter and atrial fibrillation because of scarring in the atrium, especially if the connection of the IVC to pulmonary arteries involved an intracardiac baffle (instead of an extracardiac conduit). This sometimes requires treatment such as radiofrequency ablation. There are other long-term risks, including protein-losing enteropathy and chronic renal insufficiency, although understanding of these risks is still incomplete. Some patients require long-term blood thinners. Four case reports of hepatocellular carcinoma following the Fontan Procedure were reported by physicians at the Mayo Clinic in the New England Journal of Medicine (368;18 pp 1756-1757). This group of patients may warrant screening for this malignancy, especially if the alpha-fetoprotein level is elevated.
The Fontan procedure is palliative, not curative. But in many cases it can result in normal or near-normal growth, development, exercise tolerance, and good quality of life. In 20/30% cases, patients will eventually require heart transplantation.