Truncus arteriosus (TA) is a congenital heart defect that develops during the fetal stage within the first two months of pregnancy. The condition develops when the heart blood vessels fail to separate during the heart development while the fetus is in utero. There are distinct categories of truncus arteriosus that are identified in how the heart arteries are connected. Some parts develop with a hole between the heart's ventricles (the bottom two chambers) leading to ventricular septal defect.
Normally, the right side of the heart develops in a way that the heart can pump oxygen-depleted blood to the lungs through the pulmonary artery. At the same time, the heart's left side can pump oxygenated blood to the body through the aorta. However, the truncus arteriosus defect causes the oxygenated and oxygen depleted blood to mix together before flowing to the lungs and eventually out to the body. This defect causes too much blood to enter the lungs resulting in the heart working significantly harder to continuously pump the flow of blood to the body.
Instead of being born with the pulmonary valve and an aortic valve, the newborn with truncus arteriosus develop a truncal valve (single shared valve) the controls the flow of blood out from the heart. The truncal valve is an abnormality that is usually thick and narrow, which restricts the flow of blood when leaving the heart. The abnormal valve can also leak and result in the backup of blood into the heart after it is already passed through the valve.
Approximately one out of every 10,000 children are born with truncus arteriosus, resulting in proximally 300 cases of the condition occurring in the United States every year. It is thought to develop on its own or as the result of certain genetic disorders.
- Who Is at Risk for Truncus Arteriosus?
- Common Symptoms
- Diagnosing Truncus Arteriosus
- Treating the Condition
Who Is at Risk for Truncus Arteriosus?
Because the condition is congenital, any fetus has the potential of being born with truncus arteriosus. Medical science has yet to determine the exact cause of the defect. However, there are specific factors that likely increase the potential risk of the newborn being birthed with the heart condition. These risk factors include:
- Smoking – Mothers who smoke while pregnant can increase the potential risk of birthing a baby born with a heart defect, including truncus arteriosus.
- Pregnancy-Related Viral Illnesses – Pregnant mothers who contract German measles (rubella) or other viral illnesses have an increased risk of birthing a baby with the congenital heart defect, including truncus arteriosus.
- Pregnancy-Related Poorly Controlled Diabetes – Poorly managed diabetic conditions of pregnant mothers can increase the potential risk of birthing a baby with numerous defects, including defects of the heart.
- Specific Chromosomal Disorders – Children born with velocardiofacial syndrome and DiGeorge syndrome are more likely to develop truncus arteriosus compared to children without the syndromes. This is because these conditions are the result of a defective or extra chromosome.
- Taking Specific Drugs While Pregnant – Many drugs should be avoided while pregnant because of the potential risks they can cause to the fetus, including the risk of developing heart defects like truncus arteriosus.
Any one of the risks above can cause truncus arteriosus where the largest vessel in the heart fails to develop properly by dividing into separate vessels. In addition, the walls that separate the two chambers never completely close, causing a large hole to develop (ventricular septal defect). Finally, the primary defect often involves the valve that controls the flow of blood to the ventricles that can cause the backward flow into the heart.
Typically, the doctor can diagnose truncus arteriosus within the hours or days after the child has been born. However, confirming a diagnosis will usually require extensive testing because the symptoms are often associated with other heart defects. The most common truncus arteriosus symptoms involve:
- Cyanosis where the child skin takes on a bluish or grayish tint
- Pounding heart
- Poor feeding
- Stunted Growth
- Excessive Sleepiness
- Dyspnea (shortness of breath)
- Tachypnea (rapid breathing)
Identifying a heart defect before the child leaves a hospital is not always easy. Many babies return home before displaying any common signs and symptoms associated with heart defects including truncus arteriosus. If the child experiences any of the following symptoms, it is crucial to seek out immediate emergency medical care to avoid potential death. These identical complications can include:
- Loss of consciousness
- Blue or gray coloring to the skin
- Labored, shallow or rapid breathing
Diagnosing Truncus Arteriosus
Once a newborn has been delivered, the doctor will likely perform a comprehensive examination to measure the child's weight, height, and circumference of their head. Over time, the doctor may determine there is a delay in the child's growth compared to normal measurements. The examination will also include listening to the child's lungs to assess breathing function or the presence of fluid in the lungs.
The doctor can identify a heart murmur or arrhythmia (irregular heartbeat) that produces abnormal sounds due to turbulent blood flow or restriction in the heart muscle or valves. If truncus arteriosus is identified, the pediatrician will likely recommend a pediatric cardiologist who will work with a specialized team including a pediatric cardiac surgeon.
To verify a diagnosis of truncus arteriosus the doctor will likely order a variety of tests that include:
- Echocardiogram – This test identifies the function and structure of the heart. An image is produced by intensive sound waves that bounce off of the baby's internal structures and provide moving images that can be viewed on a monitor. The echocardiogram can reveal truncus arteriosus by showing a single large valve in the heart or any abnormality of the valve in that might include a hole in the wall between the right and left ventricles. The test can also reveal the functions of the vessels and how they move blood throughout the body and show the presence of excessive elevated blood pressure in the lungs.
- X-Rays – The doctor will likely recommend an X-ray exam involving radioactive material that can produce still images of the child's internal structures and organs. This x-ray usually reveals the heart's size along with any lung abnormality or excessive amounts of fluid that are building up in the lungs.
Treating the Condition
Without surgery, truncus arteriosus can be fatal. The doctor will likely recommend multiple surgeries and procedures as the child matures. Prior to surgery, the doctor will likely prescribe drugs including diuretics to prevent fluid buildup and ionotropic agents that strengthen the contractions of the heart muscle.
If TA is diagnosed immediately after the child is born, they will likely undergo the initial surgical procedure a few weeks later. The recommended procedure will be based on the condition of the baby's health and the severity of the condition. The surgeon might choose to:
- Use a patch to close the hole that developed between the two ventricles
- Reconstruct the aorta and single large valve to allow the heart to function more normally
- Implant a conduit (tube) and valve to create a complete pulmonary artery
- Separate the pulmonary artery's upper portion from the largest single vessel
Women who have undergone a truncus arteriosus repair during their infancy should discuss with their obstetrician or cardiologist the associated risks of becoming pregnant and birthing a baby with the same condition.