Truncus Arteriosus: Causes, Symptoms, Treatment, Surgery, Risk Factors

Truncus arteriosus is a congenital and rare heart defect where the fetus or the newborn baby will have only one large blood vessel coming out of the heart instead of two separate vessels. Other than this, the patient also has ventricular septal defect, i.e. there is a hole present between the two ventricles (lower chambers) of the heart leading to mixing up of oxygenated and deoxygenated blood resulting in severe problems with the circulatory system. If truncus arteriosus is not treated on time, then it can become life threatening for the baby. Surgery is done for repairing truncus arteriosus and is often successful, especially if it is done before the baby/patient is 2 months old.

Truncus arteriosus develops during the growth of the fetus when the baby’s heart is developing, as a result of which this condition is congenital, i.e. present at birth. The cause is unknown in most of the patients.

The formation and development of the fetal heart is quite a complex process. All the babies, at a certain point, have truncus arteriosus, i.e. a single large vessel exits from the heart. However; during the normal development of the heart, there is division of this very large and single vessel into two parts. One part of it forms the lower portion of the aorta that is attached to the left ventricle; and the other part forms the lower portion of the pulmonary artery that is attached to the right ventricle. The ventricles also develop into two separate chambers, which are separated by a septum/wall during normal heart development in the fetus.

What happens in babies who are born with truncus arteriosus is that the single large vessel fails to divide into two separate vessels and also the septum or the wall, which divides the two ventricles, does not completely close resulting in a ventricular septal defect, which is a large hole present between the two ventricular chambers.

Other than the initial defects of truncus arteriosus, the valve which is responsible for controlling the flow of blood to the singe large vessel, from the ventricles, i.e. the truncal valve, is usually defective resulting in backward flow of the blood into the heart.

The exact cause of truncus arteriosus (and other congenital heart defects) is not clear. However, there are multiple factors which can increase the risk of the baby having a congenital heart condition and these factors are:

• Diabetes, which is not adequately controlled or managed during pregnancy. Poorly managed diabetes in pregnancy increases the risk of the baby being born with birth defects (including heart defects).
• If the mother has contracted a viral infection during pregnancy, such as German measles (rubella) or some other viral illness in the first trimester of the pregnancy, then there is increased risk of the baby being born with heart defects.
• Children suffering from certain chromosomal disorders, such as DiGeorge syndrome or velocardiofacial syndrome will have an increased risk for developing truncus arteriosus. The cause of these conditions is a defective or an extra chromosome.
• Certain types of medications taken during pregnancy can pose as a risk factor for the baby to be born with heart defects.
• If the mother has smoked during pregnancy, then the risk is more for the baby to be born with a heart defect.

• The baby has cyanosis, which is bluish discoloration of the skin.
• The baby has poor feeding.
• The baby is irritable.
• Has a pounding heart
• There is poor or slow growth of the baby.
• Excessive sleepiness is seen in the baby.
• The baby also suffers from tachypnea (rapid breathing) and dyspnea (shortness of breath).
• Serious symptoms in the baby for which immediate medical help should be sought include cyanosis, worsening of cyanosis, excessive sleepiness, poor feeding and poor weight gain, shallow/rapid/labored breathing and loss of consciousness.

Care and treatment for babies having truncus arteriosus is provided by a pediatric cardiologist and pediatric cardiac surgeon along with a whole team of specialized staff.
When any baby is born, its weight, height and head circumference are recorded and these measurements are continued to be taken at regularly scheduled appointments. If there is any delay of growth seen in these measurements, then it becomes a factor in diagnosis. The baby’s lungs are also auscultated to assess his/her breathing and to check if there is any danger of fluid being present in the lungs. The doctor also listens to the baby’s heart to look for any arrhythmia (irregular heartbeats) or a heart murmur, which is an abnormal sound occurring as a result of turbulent blood flow.

The following tests are done by the pediatric cardiologist to check the condition of the baby’s heart and to arrive at the diagnosis of truncus arteriosus:

Echocardiogram: Echocardiogram helps in showing the function and structure of the baby’s heart. Echocardiogram will help in revealing the single large vessel, which exits from the heart and also the ventricular septal defect, which is the hole in the wall separating the two ventricles. The abnormalities in the valve present between the ventricles and the large vessel can also be seen on echocardiogram. The flow of blood can also be visualized on echocardiogram so the back and forth circulation of the blood between the two ventricles can be seen along with the quantity of the blood flowing into the lungs of the baby. The amount of blood present in the lungs indicates the risk of high blood pressure in the lungs.

X-ray: This investigation uses radiation to generate still images of the internal structures and organs of the baby. X-ray taken of the chest will reveal the size of the heart along with the excess fluid in the lungs and the abnormalities present in the lungs.

Surgery is needed to repair the Truncus Arteriosus and its associated heart defects in the baby. Multiple surgeries may be needed as the child grows. Medications can be given before performing the surgery to improve the condition of the heart.

Medications for Truncus Arteriosus that are prescribed before surgery include:

• Inotropic agents are the medications, which help in strengthening the contractions of the heart.
• Diuretics, also known as water pills, will increase the volume and frequency of urination thus prevents fluid from accumulating in the body.

Surgery is required for majority of the infants suffering from truncus arteriosus within the first few weeks after the baby being born. The type of surgical procedure done depends on the condition of the baby. After the corrective surgical procedure, the child needs lifelong follow-up care with his/her cardiologist for monitoring the heart health of the baby. It will be recommended that the child limit his/her physical activity, especially rigorous and competitive sports. Antibiotics to prevent infections need to be taken by the child before any dental procedures or surgical procedures.

Surgery that is done usually comprises of:

• Separating the upper part of the pulmonary artery from the large, single vessel.
• Closing the defect or hole using a patch in the septum/wall between the two ventricles.
• Placing a conduit or a tube and valve to connect the upper portion of the pulmonary artery with the right ventricle thus creating a new and complete pulmonary artery.
• Reconstructing the aorta and the single large vessel to create a new and complete aorta.

As the child keeps on growing and the artificial conduit does not grow along with the child; so as a result, follow-up surgeries are required to replace the conduit valve as the child gets older. These follow-up surgeries can be delayed by doing cardiac catheterization using an inflatable balloon tip to widen a narrowed or an obstructed artery.

Women who have had truncus arteriosus in infancy which was repaired and who plan on getting pregnant need to consult with their cardiologist and obstetrician who specialize in dealing with high-risk pregnancies before trying to get pregnant. Pregnancy may not be recommended if the lung damage before the surgery has been severe. Other than this, some medicines which are taken for heart conditions can be harmful to the fetus.

Congenital heart defects including truncus arteriosus are difficult to prevent in most of the cases. Consulting a genetic counselor or cardiologist is recommended if there is a family history of heart defects or if the baby is suffering from a congenital heart defect before attempting to become pregnant. The following steps can be taken before becoming pregnant to ensure that the baby is born healthy and without any heart defects:

• Certain types of medications, which can cause harm to the unborn baby, should be avoided before becoming pregnant and during pregnancy.
• It is important to get vaccinated before getting pregnant against infections, as certain viral infections, such as German measles, if contracted during pregnancy can be very detrimental to the baby. It is important to be up to date regarding the immunizations before getting pregnant.
• It is important to keep your diabetes under control if you are planning to get pregnant. Women should talk to their doctors regarding associated risks of diabetes with pregnancy and the best way to manage diabetes in pregnancy.
• It is important to take folic acid throughout the pregnancy to prevent birth defects of not only heart, but also of brain and spinal cord.