Common Truncus (also called truncus arteriosus)
Common truncus or truncus arteriosus is an uncommon congenital heart defect where a baby is born with a single blood vessel (called a truncus) coming from the main pumping chambers of the heart (the ventricles) instead of two vessels (one from each ventricle). This single blood vessel also shares one valve coming both heart chambers and the single valve is typically positioned over a hole between the two heart chambers. In rare cases of common truncus, the single vessel is located almost completely on one ventricle rather than positioned over both. In addition, the pulmonary arteries that take blood to the lungs come off from this common single blood vessel. Very early in fetal life the developing heart is formed with a truncus vessel, and as development proceeds, this vessel is supposed to divide into two: the aorta and the pulmonary artery. For an unknown reason, this division of the vessel does not occur in some babies, and thus they are born with this particular heart defect called “common truncus”. Babies will typically be bluish/grey (called cyanosis) because not all the blood going to the body will have passed through the lungs to receive oxygen.
Common Truncus occurs rarely, affecting 5-15 children of 100,000 live births. It is one of the least common of congenital heart defects, making up 1-2% of babies born with heart defects. About 5% of stillborn babies will have Common Truncus abnormalities.
Common Associated Conditions
Babies with Common Truncus will typically have other problems with the heart and vessels. Heart valves are often abnormal, and leakage through the heart valves occurs in at least 20% of the children with this condition. Also, the very important blood vessels that bring oxygen to the heart muscle (the coronary arteries) are abnormal in many cases. About 30-35% of babies with Common Truncus will have a condition called DiGeorge syndrome (also called velocardiofacial syndrome), a genetic condition involving a small thymus glad, and a number of other facial features caused by absence of part of a chromosome. They may also have kidney, bone and digestive tract abnormalities.
Short-term Treatment and Outcomes
Babies with common truncus will need surgery very early in life. If not, the lungs will become damaged by the excessive blood flow within 3 or 4 months, and then the outlook for the baby will be poor. Before surgery, babies will usually receive digoxin to strengthen the heart as well as diuretics to treat the congestive heart failure by removing excess fluid from the body.
At the time of surgery the hole between the ventricles is closed and the single truncus vessel is directed to take blood away from the left ventricle to bring blood to the body's circulation. A conduit or chamber is created from the right ventricle to which the pulmonary arteries are attached so that blood from the right side of the heart can be directed to the lungs to be oxygenated. The outcome from this surgery has greatly improved in recent years. Typically there is an 80-90% survival rate 10 to 20 years following the surgical repair for common truncus.
Families will be offered genetic counseling since in many cases there is increased risk of heart defects occurring in subsequent pregnancies.
Long-term Treatment and Outcomes
Long-term, many children require further surgeries to enlarge the outflow conduit from the right ventricle. They may also have difficulties with the valve in the truncus vessel that may leak and overload the left side of the heart. Other complications can develop, such as conduction problems if the nerves that cause the heart muscle to contract do not function correctly. If this occurs, the heart's rhythm and rate will be affected.
Periodic examinations from a cardiologist will be necessary throughout life, with tests such as echocardiograms, stress tests and Holter monitoring (collecting information about the heart's electrical activity that makes it beat in a regular rate and rhythm). This will be essential so that complications can be quickly detected and treated.
Antibiotics will be necessary when individuals have dental work so that the bacteria released in the mouth do not travel to the heart and cause an infection of the heart (called endocarditis).
Babies with Common Truncus can be very ill, depending on how well the vessels and pumping chambers function to supply vital organs with oxygen and how overloaded the heart becomes from having only a single vessel for outflow of blood. A serious concern is any infection that might readily spread through the body (called sepsis). Babies can go into a shock-like condition because of the overload of fluid in the heart and lungs (called cardiogenic shock). They will typically develop congestive heart failure, which is displayed by rapid breathing and heart rate, fatigue and sweating with feeding, and general lack of activity. They will also have heart enlargement (cardiomegaly).
After heart surgery some children (2-15%) will develop a condition called post-pericardiotomy syndrome. The child will have chest discomfort, fever and evidence of "inflammation" on blood tests. The cause of this condition is unknown and it usually disappears in a few days.
Children with truncus will remain at increased risk for infection of the heart (endocarditis) and heart valves and will need to take antibiotics before dental and surgical procedures in order to prevent this occurrence. They will require long-term regular follow-up by a pediatric cardiologist so that any symptoms of heart failure, infection or arrhythmia can be prompted detected and treated.
Implications for Children's Development
There is great variability in terms of how much effect common truncus has on a child's development. In most cases the surgery is carried out in the early weeks of life and the baby makes an excellent recovery in all respects.
Children with significant cardiac conditions that have been successfully corrected by surgery typically grow well and can keep up with other children. Some studies show that the ventricles do not ever function at the level of a normal heart, which may affect children's capacity for vigorous exercise. A cardiologist will need to be consulted in order to determine if a child's activity needs to be limited due to heart failure or rhythm disturbances.
Children with heart conditions should have excellent dental care since the mouth is a source of bacteria that can be passed on to the heart and cause infection.
For more information, including resources for parents and general information about congenital cardiac conditions, visit the following websites:
- National Center for Biotechnology Information
- CDC Congenital Heart Defects Information
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