Truncus arteriosus occurs when the great arteries do not develop normally while the baby is in the mother’s womb. In this defect, instead of two large vessels that arise from the base of the heart, there is only one vessel. It is one of the rarer forms of congenital heart disease comprising about 1% of congenital heart defects and is slightly more common in boys than girls. It is also slightly more common in children of diabetic mothers.
In the normal heart, there are two large blood vessels that take blood away from the heart. The blood vessel that normally arises from the right heart, the pulmonary artery, takes blue blood from right lower chamber (the right ventricle) to the lungs. The blood vessel that normally arises from the left heart, the aorta, takes red blood from the left lower chamber (the left ventricle) out to the body.
In babies with truncus arteriosus there is only one large blood vessel (1) leaving the heart instead of two. This single vessel supplies blood to the body and branches from this large vessel, called pulmonary arteries, (2) supply blood to the lungs. The branches leading to the lungs may take a variety of forms, and may exit the single large vessel from different spots. The size and location of these vessels are important factors for the surgeon to consider when planning the operation. There is also a large hole in the wall that separates the right and left ventricles called a ventricular septal defect or VSD (3). This hole allows complete mixing of blue and red blood in the ventricles.
Other heart problems that may be seen in association with truncus arteriosus include leakage of the truncal valve, abnormal coronary arteries, and/or narrowing or complete interruption of the aortic arch.
About 33% of babies with truncus arteriosus have a genetic problem called DiGeorge syndrome. This occurs when part of chromosome is lost during the earliest stages of fetal life. In addition to heart problems, children with DiGeorge syndrome may have decreased ability to resist viral infections, low blood calcium, cleft palate, kidney problems, changes in facial features, and learning problems.
Truncus arteriosus is a serious heart problem that is usually diagnosed during early infancy. If not treated, 85% babies die during the first year of life. The main problem caused by the defect is too much blood flow to the lungs causing congestive heart failure with symptoms of rapid breathing, clammy sweating, poor feeding, and slow growth. These symptoms are usually seen within the first few days to weeks of life. Cyanosis, a bluish color seen in the lips and nailbeds is also usually present due to mixing of blue and red blood in the ventricles. Due to the extent of the problems caused by truncus arteriosus, open-heart surgery is usually done as soon as possible.
Prenatal diagnosis: Truncus arteriosus can be diagnosed before birth by a fetal echocardiogram or heart ultrasound as early as 18 weeks into the pregnancy. This test is done when there is a family history of congenital heart disease or when a question is raised during a routine prenatal ultrasound.
Symptoms: Symptoms of congestive heart failure most often develop within days or week of birth and are worse when there are other problems such as leakage of the truncal valve or a narrow aortic arch. Symptoms of congestive heart failure in infants include rapid breathing, clammy sweating, poor feeding, and poor growth. Mild cyanosis, a bluish color of the baby’s lips and nailbed, is most often present but can be difficult to detect by looking at the baby.
Physical findings: Most babies with truncus arteriosus are born at term and are a normal weight and length (since before birth the baby’s oxygen comes from the mother). After birth, the baby’s lips and fingernails may look blue. A heart murmur is most often present. If congestive heart failure is present, the heart rate and breathing rate will be increased, and the liver may be enlarged.
Medical tests: The suspected diagnosis is confirmed by an echocardiogram. An oxygen saturation test is used to measure the blood oxygen levels. Other tests include an electrocardiogram and chest x-ray. Sometimes, a heart catheterization may is needed to help the doctors plan the surgery.
The main treatment for truncus arteriosus is open-heart surgery, done as soon as possible after the diagnosis is made. The operation uses a conduit which is a tube made of either Dacron with a pig valve inside it or a donated human valve and artery (called a homograft valve). One end of the conduit/homograft is sewn into the right ventricle (1) and the other end is sewn into the pulmonary artery (2). The branch vessels leading to the lungs are removed from the truncus and sewn into the conduit. Sometimes repair or replacement of the truncal valve (3) is needed as well. The VSD is also closed by sewing a patch over it (4).
Medicines such as digoxin and lasix are often used to treat symptoms of congestive heart failure.
Most children with truncus arteriosus will need their conduit/homograft replaced one to two times before they reach adulthood. This is needed because the child "outgrows" the conduit and also because calcium tends to collect in the conduit causing a narrowing and thus obstruction to blood flow. Fortunately, re-operation to replace the conduit is usually tolerated well and carries a low risk for complications.
In leading centers, the surgical success for early repair of truncus arteriosus in babies has improved greatly with 90% survival. Re-operation to replace the conduit will be needed periodically but these operations are quite low risk to the child.
Possible long-term medical problems for children born with truncus arteriosus include conduit obstruction and/or leakage of the truncal valve requiring re-operation.
SBE prophylaxis: Throughout their lives, children with truncus arteriosus are at increased risk for subacute bacterial endocarditis (SBE). This is an infection of the heart caused by bacteria in the blood stream. Children with heart defects are more prone to this problem because of the altered flow of blood through the heart. It can occur after dental work or medical procedures on the GI or respiratory tract because these procedures almost always result in some bacteria entering the blood. SBE can usually be prevented by taking an antibiotic before these procedures.
Exercise guidelines: An individual exercise program is best planned with the doctor so that all factors can be included. Children with truncus arteriosus are usually restricted from vigorous or competitive sports but can participate in recreational sports. It is important for them to always be able to self-limit their activity, that is, to rest whenever they feel the need to do so. The children can usually participate in gym class but should be allowed to self-limit their level of exertion and they should not be graded (which could increase the pressure to exceed their natural limits).
Bove EL, Lupinetti FM, Pridjiian AK et al. Results of a policy of primary repair of truncus arteriosus in the neonate. J Thorac Cardiovasc Surg 1993; 105: 1057-1056.
Bove EL, Mosca RS. Lessons learned in truncus arteriosus surgery. Adv Card Surg 1995;6:91-101.
Mair DD, Edward W Julsrud Pr et al. Truncus arteriosus. In Allen HD, Gutgesell HP, Clark EBB & Driscoll DJ, eds. Moss and Adam’s Heart Disease in infants, children, and adolescents, Vol II, Philadelphia, PA: Lippincott Williams & Wilkins. 2001: 910-923.
Mavroudis C, Backer CL. Truncus arteriosus. In Pediatric Cardiac Surgery, Mavroudis C & Backer CL, eds. St. Louis MO: Mosby 1994: 237-246.
Written by: S. LeRoy RN, MSN, CPNP
Reviewed January, 2010