A single ventricle is a complex congenital heart defect where only one ventricle, instead of two, has formed. Although there are heart lesions such as tricuspid atresia and mitral atresia, in which one ventricle is very small (hypoplastic), these cases still have two ventricles even though only one is big enough to function as a pump. Pediatric cardiologists usually use the term single ventricle when either the mitral and tricuspid valves, or a single or common atrioventricular valve, allow blood to empty into the same chamber or ventricle.
Sometimes, heart defects that are not truly single ventricles may be treated the same way as a single ventricle. In all of these cases, the blue (low oxygen content) blood and red (high oxygen content) blood are pumped from the right and left atrium to the single ventricle where they mix. This mixed blood then gets pumped to both the pulmonary arteries (which go to the lungs) and to the aorta (which goes to the body). In some cases, there is an obstruction in the aortic or pulmonary valves or the area underneath them. This will determine how much blood gets pumped to the body versus the lungs. It will also determine what types of surgeries are required.
Eventually, all people with a single ventricle will need one or more surgeries which allow the blue blood to drain to the lungs by gravity, flow to the single ventricle, and get pumped to the body. This is known as a single ventricular, univentricular, or Fontan type of repair.
Symptoms include difficulty breathing or feeding and/or cyanosis (blue color).
The diagnosis is usually made soon after birth after the baby develops symptoms of difficulty breathing or feeding and/or cyanosis (blue color). The degree of blueness depends on the exact type of heart defect, but usually, there is at least some degree of cyanosis. Sometimes the oxygen level is measured with a machine called a pulse oximeter. Babies may not be blue, but the level of oxygen is lower than it is supposed to be when measured with a pulse oximeter. The diagnosis is further suspected by subtle abnormalities on the physical examination though there may not be any significant abnormal murmurs. The diagnosis is then confirmed with an echocardiogram.
Early treatment may include using a drug to keep the patent ductus arteriosus (PDA) from closing. A PDA will allow blood to flow either to the lungs or to the body in cases of obstruction to blood flow to one of those places. If needed, the PDA is kept open with a medication called prostaglandin.
In the case of obstruction at or below the pulmonary valve so that not enough blood goes to the lungs to get oxygen, the PDA is used only if the baby is too blue to survive and grow. The PDA can only be kept open with medication for a short while so that surgery will then be required to place a tube (shunt) between the aorta and the pulmonary artery to help increase blood flow to the lungs. This is known as a Blalock-Taussig shunt or BT shunt.
Typical Heart - Anterior
If the initial problem is a lack of enough blood flow to the body, due to aortic or subaortic stenosis, a procedure is needed which allows blood to get to the body without any obstruction. This procedure is usually a Damus procedure where the aorta and main pulmonary arteries are combined as one so blood flows from the heart to the body through a “combined” vessel. Since the main pulmonary artery is cut from the right and left pulmonary arteries, another procedure is needed at the same time to allow blood to flow to the lungs to get oxygen. This additional procedure is the Blalock-Taussig (BT) shunt.
In some ventricles, there is no obstruction to the lungs or to the body. In those cases, similar to a ventricular septal defect (VSD), blood will preferentially flow to the lungs since that is the path of least resistance. Unlike a VSD, which can be closed with surgery, the single ventricle cannot be divided into separate ventricle with one ventricle pumping to the lungs and the other pumping blood flow to the body. Therefore, a different type of procedure is needed to prevent too much blood flow to the lungs. This procedure is called a pulmonary artery band and is essentially tying a noose around the pulmonary artery to constrict the vessel and decrease blood flow through it. Usually, this is outgrown after six months or sometimes longer.
Eventually, usually after about six months, another procedure is needed to get more blood flow to the lungs. This is because the BT shunt and the pulmonary artery band eventually do not allow enough blood flow to the lungs, and the infant will become more cyanotic. The next surgery is usually a procedure where the surgeon connects the superior vena cava to the right pulmonary artery so that all the blood from the upper half of the body goes to the lungs by gravity. This is known as a Glenn procedure.
Eventually, more oxygenated blood is needed as the Glenn shunt is outgrown. The inferior vena cava (which contains all the blue blood from the lower half of the body) is then connected to the right pulmonary artery by a tube (either within or outside the right atrium or by other methods). In this manner, all the blue blood from the body (upper and lower half) flows directly to the pulmonary artery. Since the blue blood no longer mixes with the red blood, the degree of cyanosis decreases. This is called a Fontan procedure.
The risks of open-heart surgery always include bleeding, infection and the need for cardiopulmonary bypass. Special risks of the BT, Glenn and Fontan shunts include injury to the nerve that supplies the diaphragm resulting in paralysis of the diaphragm. In addition, the pulmonary artery may become narrowed in the area that the BT shunt, Glenn or Fontan shunts are sewn to the pulmonary artery.
Although it is not a cure, the Fontan procedure or univentricular repair is a method by which children can have functional lives. Long term, there may be rhythm abnormalities, problems with heart function, and swelling. There is also the risk of stroke if blue blood goes to the body instead of the lungs (right to left shunt). Therefore, children with single ventricle should have lifelong follow-up by a pediatric cardiologist. There is always a risk of bacterial endocarditis so preventive measures are indicated for life.