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Truncus arteriosus is a congenital heart defect where deoxygenated blood is pumped throughout the body, causing congestive heart failure.
In a normal heart, the right ventricle pumps the “blue,” oxygen-deficient blood to the lungs, the blood gets oxygen, comes back to the left side of the heart as “red,” oxygen-rich blood and gets pumped to the body by the left ventricle. There is a wall between the two ventricles that keeps the “blue” and “red” blood from mixing.
In truncus arteriosus, the blood that is pumped out of the heart is a mixture of “blue” and “red” blood. This means that the oxygen level of the blood is not 100%, like it is when the body gets only “red” blood. Usually the oxygen level is not so low that it is dangerous, but it will be lower than normal.
In the normal heart, the amount of blood going to the lungs is the same as the amount to the body.
In truncus arteriosus, the blood leaving the heart has two choices of where to go: to the lungs or to the body. After babies start breathing, it becomes much easier for the blood to go to the lungs than to the body, so extra blood will easily flow to the lungs.
The heart will need to pump harder to pump this extra blood plus the blood that the body needs. As the heart works harder, sometimes 3-4 times as hard as normal, babies will breathe faster and have trouble eating. Eventually the heart may not keep up with the extra work it needs to do. At that time babies can be very sick.
In most cases, there is no known specific cause for truncus arteriosus. DiGeorge syndrome is often associated with truncus arteriosus.
Diagnosing Truncus Arteriosus
Truncus arteriosus is diagnosed in various ways, including:
- Echocardiogram - an ultrasound of the heart.
- Fetal echocardiogram - an ultrasound of the heart before birth
- Others may not be detected until after birth
- Failing the newborn pulse oximetry screen. The diagnosis would be confirmed with an echocardiogram
If the diagnosis of truncus arteriosus is discovered before birth, then your baby’s delivery may be planned. He or she will go to the neonatal intensive care unit (NICU) after birth. An echocardiogram will be done and the baby’s breathing and oxygen level will be monitored.
The same things would happen if the diagnosis is made after birth. Some babies may need medications to support the heart as it does this extra work.
Eventually, the baby will require surgery.
Surgery for Truncus Arteriosus
Surgery for truncus arteriosus involves a few steps that try to fix the heart abnormalities. Surgery is usually done soon after birth, typically within the first week of life.
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The surgeon will close the VSD so that the left ventricle can pump blood to the truncus, which will be used as the aorta.
The surgeon removes the pulmonary artery branches from the truncus and connects them to the right ventricle using a conduit. A conduit is a tube made from a vein or prosthetic material. It provides an open pathway for blood to be pumped from the right ventricle to the lungs.
If the truncal valve (between the ventricle and the truncus) leaks a lot or does not open well, the surgeon will also try to repair the valve.
After the Surgery
Most patients who have truncus arteriosus will need repeat surgeries later in life.
The conduit that is placed to connect the right ventricle to the pulmonary arteries does not grow with the patient. As the child and the rest of the heart grow, it will become harder for the heart to pump blood through the conduit.
The valve in the conduit often starts to leak. Eventually the conduit will need to be replaced.
Sometimes a cardiac catheterization procedure will be done to measure pressures in the heart. During the cardiac catheterization, a balloon may be used to open up areas of the conduit or the rest of the pulmonary arteries to improve any obstruction. When this is no longer effective, the patient will need a repeat surgery to replace the conduit.
The timing for replacement of a conduit is unpredictable. It is usually within 5-10 years from the initial surgery.
In general, the long-term prognosis for truncus arteriosus is good.
Although patients may need additional surgeries or procedures, they are not typically on a lot of medications. Their activities are typically not limited.
Some patients may develop heart rhythm abnormalities later in life, requiring medications or pacemakers.
When one family member has a congenital heart defect, there is an increased risk in other family members. A genetic counselor can better determine what the risk would be for future pregnancies.
If the baby has DiGeorge syndrome, parents may be tested to see if they carry the gene abnormality seen in DiGeorge syndrome.