|This image is reprinted with permission from University of Michigan Congenital Heart Center.
Some congenital (present at birth) heart defects cause oxygen-rich blood and oxygen-poor blood to mix in your circulation. This can result in your body not receiving the amount of oxygen it needs for healthy functioning. For children with single ventricles that support then entire circulation, staged surgical procedures are necessary to separate the venous and arterial circulations. It is said that these children will proceed down a "single ventricle/Fontan pathway." The Fontan procedure is a surgical technique used to separate oxygen-rich and oxygen-poor blood, but the surgery does not create a normal circulatory pattern. For example, in a normal heart, the two lower heart chambers (ventricles) act as pumps, with one ventricle pumping blood to the body and the other pumping blood to the lungs. After the Fontan procedure, only one chamber pumps blood, and it must be strong enough to pull blood that is passively moving through the lungs into the heart and then pump it out to the body.
Keep reading for descriptions of the Fontan procedure during childhood and continuing support needed as an adult.
The Fontan Procedure in Childhood
In the Fontan procedure, surgery is performed to connect the vein (inferior vena cava) carrying oxygen-depleted blood from the lower body directly to the pulmonary arteries, which carry blood to the lungs to pick up oxygen. Prior to the Fontan procedure, typically the venous blood from the upper body is directly connected to the pulmonary arteries by surgery (bidirectional Glenn or hemi-Fontan). The inferior vena cava is connected to the pulmonary arteries using a tube that bypasses the heart or by creating a baffle within the heart to direct the blood upward to the lungs. The surgical methods used to establish these connections have developed over the years so there are several types of Fontan procedures that have been used in the past. Some use reconstructed pathways within the atrium (intracardiac Fontan), while others use tubes to connect the inferior vena cava to the pulmonary arteries outside of the heart (extracardiac Fontan). Sometimes because of the inefficiency in circulation related to some types of Fontan surgery, new connections (Fontan revision) need to be made.
After completion of the Fontan procedure, the blue (oxygen-poor) and red (oxygen-rich) blood circulations are fully separated. However, there is now no pumping chamber in the heart to propel blood through the lungs. Blood passively moves through the lungs and returns to the heart via the pulmonary veins. By virtue of not having a pumping chamber on the venous side of the circulation, the pressure within the Fontan circuit must always be higher than the chamber that the blood from the lungs passes into. This results in the pressure within the veins being higher than normal.
Babies who undergo the Fontan procedure have only one functioning ventricle to pump blood to the body. In order for the procedure to succeed, the blue blood from the body must be able to pass through the lungs easily to pick up oxygen since there is no pumping chamber that pushes blood directly through the lungs. Additionally, the ventricle that pumps to the body needs to be reasonably healthy and strong enough to “suck” blood from the lung (pulmonary) circulation and propel it forward into the body. If it is not strong enough, the procedure will fail. The valves related to the main ventricle also need to function correctly. Leakage or narrowing of these valves will place additional strain on the ventricle.
Also, after the intracardiac Fontan procedure, there is a risk that the heart’s right upper chamber (atrium) will become stretched, although this occurs less frequently with today’s more refined surgical techniques. If the atrium is stretched, an abnormal heart rhythm may result. Abnormal heart rhythm will interfere with the function of the heart in pumping enough blood to the body, resulting in fatigue, fainting and heart failure.
Because the pressure in the veins and lung vessels needs to be higher to allow blood to passively pass through the lungs to return to the heart, this places additional stress on the other organs of the body, including the liver, gastrointestinal (GI) tract and kidneys. The resultant congestion of venous blood in these organs can cause problems including fibrosis/cirrhosis of the liver, kidney dysfunction and problems with absorption of nutrients from the GI tract. Sometimes these problems become more of an issue than the pumping function of the heart itself. It is becoming increasingly clear that although the Fontan operation can restore separation of “blue” blood from “red” blood into their respective circulations, long-term success of this circulation is not expected. It is possible that heart transplantation may eventually have to be performed, but the relatively scarce supply of these organs means that many will not be able to receive them. Furthermore, the multiple exposures of these patients to blood transfusions may affect the ability to find a heart that “matches” and will not be rejected quickly.
The Fontan Procedure in Adulthood
Most Fontan procedures are performed during childhood, but the procedure is sometimes performed in adults. After a Fontan procedure, close follow-up with a cardiologist will be required across the lifespan.
There are many potential complications in patients who have undergone a Fontan procedure. Since there is no pump to push blood from the inferior vena cava (IVC) to the pulmonary arteries, the pressure in the IVC is higher than normal. This can lead to liver failure. It is important for patients not to consume alcohol and to limit medications that can damage the liver.
The body may form extra blood vessels that reroute blue blood away from the lungs and back to the body’s circulation (venovenous collaterals). This can cause cyanosis and make the patient appear blue, and it can lead to progressive fatigue. Some of these vessels can be blocked off (occluded) in a hospital’s catheterization lab.
Patients can also retain fluid and have swelling, especially of the feet, ankles or abdomen. This can result from heart failure, obstruction of blood flow to the lungs, or a condition called protein-losing enteropathy (PLE). In PLE, the body is unable to absorb proteins from the digestive tract. Other symptoms include abdominal pain and diarrhea. There are currently no standard treatments to cure PLE, but your cardiologist may try different medications to improve symptoms. Another rare complication of the Fontan procedure is plastic bronchitis. Patients can have difficulty breathing and begin coughing up thick protein casts. They are called casts because they look like the casts of the bronchial tree. These casts can be very difficult to clear and may be life-threatening if they cause airway obstruction. Some patients require admission to the hospital for more aggressive treatments to remove these secretions.
It is important to consult your cardiologist about the kind and level of activity that is appropriate for you, given your condition, and to check with him or her before trying new activities.