Hearing that your newborn baby has a serious heart condition is one of the most frightening and overwhelming experiences a parent can face. When the diagnosis is a rare and complex defect like truncus arteriosus, the news can be filled with confusing terms and profound uncertainty. Truncus arteriosus is a congenital heart defect (CHD), meaning it is a problem with the heart’s structure that is present at birth. It is a life-threatening condition that requires open-heart surgery in early infancy. While the journey ahead is challenging, it is vital for parents to know that remarkable advancements in pediatric cardiac surgery have transformed the outlook for these children. With timely diagnosis and expert care, babies born with truncus arteriosus can have a successful repair and go on to lead active, fulfilling lives.

To understand truncus arteriosus, it first helps to picture a normal heart. A healthy heart has four chambers and acts as a powerful, two-sided pump. The right side of the heart pumps oxygen poor (blue) blood to the lungs through a large vessel called the pulmonary artery. The left side of the heart pumps oxygen rich (red) blood to the rest of the body through a separate large vessel called the aorta. A muscular wall called the ventricular septum separates these two pumps, ensuring that blue blood and red blood do not mix.

In truncus arteriosus, this elegant and separate design fails to form correctly in the womb. Instead, the heart has several major structural defects:

1. A Single Great Vessel (The Truncus): Instead of having two separate arteries leaving the heart (the aorta and the pulmonary artery), there is only one large, single vessel. This common trunk, the truncus arteriosus, arises from the bottom chambers of the heart.
2. A Ventricular Septal Defect (VSD): There is always a large hole in the wall separating the two lower pumping chambers (the ventricles).
3. An Abnormal Truncal Valve: The single valve that controls blood flow out of the heart and into the truncus is often defective. It may have too many or too few leaflets (the small flaps that open and close), and it may be narrowed (stenotic) or leaky (regurgitant).

This combination of defects creates a critical blood circulation problem. Because of the large VSD, oxygen poor blood from the right ventricle and oxygen rich blood from the left ventricle mix together completely. This mixed blood is then pumped out through the single truncus. From this common vessel, some blood travels to the lungs, and some travels to the body. This leads to two major, life-threatening problems:

• Too much blood flow to the lungs: The lungs receive a flood of blood under very high pressure, which can quickly lead to fluid buildup and heart failure.
• Too little oxygen for the body: The blood circulating to the body does not have a normal amount of oxygen because it is mixed with oxygen-poor blood. This causes the baby’s skin to have a bluish tint (cyanosis).

Truncus arteriosus is caused by a problem in heart development during early pregnancy. In a typical embryo, the heart begins with a single large vessel, the truncus arteriosus. During the first eight weeks of gestation, a complex process of division and spiraling occurs, where this single trunk separates to form the distinct aorta and pulmonary artery. In a baby with truncus arteriosus, this crucial separation process fails to happen, leaving the heart with the single vessel it started with. The VSD forms because the wall between the ventricles is supposed to fuse with the newly separated arteries, and without that separation, the wall remains incomplete.

For the vast majority of cases, the specific reason why this developmental process fails is unknown. It is not caused by anything the parents did or did not do during pregnancy. It is believed to be a complex interplay of genetic factors and possibly environmental influences that disrupt the intricate signals guiding heart formation at a critical time.

Truncus arteriosus is a congenital condition, meaning the baby is born with it. While most cases occur for no known reason, researchers have identified several key risk factors and genetic associations.

Genetic Associations: The strongest known link is to a specific genetic condition called 22q11.2 deletion syndrome, also known as DiGeorge syndrome or velocardiofacial syndrome. According to the U.S. Centers for Disease Control and Prevention (CDC), about one-third of all babies born with truncus arteriosus also have this genetic syndrome, which is caused by a small missing piece of chromosome 22. For this reason, all infants diagnosed with truncus arteriosus are typically recommended for genetic testing. Other, rarer genetic mutations have also been linked to the condition.

General Risk Factors for Congenital Heart Defects: While a specific cause is rarely found, some general factors during pregnancy may slightly increase the risk of having a baby with a congenital heart defect. These include:

• A parent who has a congenital heart defect themselves.
• Certain viral infections during pregnancy, like rubella (German measles).
• Poorly controlled maternal diabetes.
• The use of certain medications during pregnancy, such as some acne or seizure medications.
• Smoking or consuming alcohol during pregnancy.

It is important to reiterate that these are general risk factors and that most cases of truncus arteriosus occur in pregnancies with no identifiable risks.

Symptoms usually appear within the first few days to weeks of life, as the baby’s body struggles to adjust to the mixed blood flow and increasing oxygen demand.

The most common signs and symptoms include:

• Cyanosis: A noticeable bluish discoloration of the skin, lips, and nail beds. This is caused by the lower-than-normal level of oxygen in the blood circulating to the body.
• Breathing Difficulties: The baby may breathe very rapidly (tachypnea) or have labored breathing due to the excess blood flow flooding the lungs.
• Poor Feeding: The baby may tire very easily during feeding, sweat while trying to eat, and may not gain weight appropriately (failure to thrive). The work of breathing and pumping blood is so taxing that they have little energy left for feeding.
• Excessive Sleepiness or Lethargy: The baby may seem unusually drowsy and difficult to wake.
• Pounding Heart and Heart Murmur: A doctor listening to the baby’s chest will hear a prominent heart murmur, which is the sound of turbulent blood flow caused by the heart defect. The baby’s heartbeat may also feel unusually strong or pounding.

Prenatal Diagnosis: Thanks to advancements in ultrasound technology, truncus arteriosus is often diagnosed before a baby is born.

• It may first be suspected during a routine prenatal ultrasound.
• If a heart problem is suspected, a fetal echocardiogram will be recommended. This is a detailed ultrasound performed by a pediatric cardiologist that focuses specifically on the structure and function of the baby’s heart in the womb.
• A prenatal diagnosis is incredibly valuable. It allows the family time to learn about the condition and prepare, and it ensures that the baby can be delivered at a specialized medical center with a pediatric cardiac intensive care unit (CICU) and pediatric cardiac surgeons ready to provide immediate care.

Postnatal Diagnosis: If not detected before birth, the diagnosis is usually made shortly after, when the baby develops symptoms.

• Pulse Oximetry Screening: A low reading is a major red flag for a critical CHD like truncus arteriosus.
• Echocardiogram: This is the primary diagnostic tool after birth that confirms the structure of the heart and presence of one large artery.
• Other tests, such as a chest X-ray and an electrocardiogram (ECG), will also be done to assess the heart and lungs.

Clinically, a detailed echo is the gold standard.

Surgical repair is the only effective treatment for truncus arteriosus, typically performed in the first few weeks of life. The goal of the surgery is to re-route the blood flow to create a more normal, two-sided circulatory system. The standard procedure involves several key steps:

1. Closing the VSD: The surgeon closes the large hole between the two ventricles with a patch, typically made of synthetic material. This patch is placed in such a way that it directs all of the oxygen rich (red) blood from the left ventricle out into the truncus.
2. Creating a New Aorta: With the VSD closed, the original truncus and its valve now function as the new aorta, carrying oxygen rich blood to the body.
3. Creating a new pathway from the right ventricle to the lungs (via a conduit or graft). This conduit may be a homograft (a donated human aorta or pulmonary artery) or may be made from other biological or synthetic materials.

Long-Term Management and Outlook: The initial surgical repair is life-saving, but it is not a permanent cure. The child’s heart, while repaired, is not completely normal, and they will require lifelong care from a cardiologist who specializes in congenital heart disease.

• Lifelong Follow-up: Regular check-ups, including echocardiograms and other imaging, are needed to monitor heart function.
• The Conduit: The surgically placed conduit that connects the right ventricle to the pulmonary arteries does not grow with the child. This means that it will eventually become too small or may wear out over time. All individuals who undergo a truncus arteriosus repair will require one or more future procedures to replace this conduit.
• Other Potential Issues: Long term follow-up also monitors for other potential issues, such as a leaky truncal valve (which now functions as the aortic valve) or heart rhythm problems (arrhythmias).
• Activity: After recovering from surgery, most children with repaired truncus arteriosus can be fully active and participate in most sports, though some recommendations for activity modification may be made by their cardiologist.

A diagnosis of truncus arteriosus is a journey that begins with shock and fear but leads to a testament of resilience and medical progress. This rare and complex congenital heart defect requires immediate and highly specialized care, including major open-heart surgery in the first weeks of life. While the path involves lifelong monitoring and the certainty of future procedures to replace the pulmonary conduit, the success of the initial surgical repair is remarkable.

• Centers for Disease Control and Prevention (CDC). (2023). Facts about Truncus Arteriosus. Retrieved from https://www.cdc.gov/ncbddd/heartdefects/truncusarteriosus.html
• The Children’s Hospital of Philadelphia (CHOP). (n.d.). Truncus Arteriosus. Retrieved from https://www.chop.edu/conditions-diseases/truncus-arteriosus
• Mayo Clinic. (2022). Truncus arteriosus. Retrieved from https://www.mayoclinic.org/diseases-conditions/truncus-arteriosus/symptoms-causes/syc-20352535