Truncus arteriosus (TA) is a rare and complex congenital heart defect, meaning it is a structural problem of the heart present at birth. This serious condition involves a failure in the normal development of the major blood vessels leaving the heart, leading to life-threatening complications that require immediate medical intervention. Understanding this defect, its symptoms, and the necessary treatment is important for parents and caregivers facing this diagnosis.
Defining the Defect and Causes
The fundamental problem in truncus arteriosus is that only one large artery, called the truncus, arises from the heart, instead of the normal two separate arteries: the aorta and the pulmonary artery. In a healthy heart, the aorta carries oxygen-rich blood to the body, and the pulmonary artery carries oxygen-poor blood to the lungs. With TA, the single common trunk vessel receives blood from both the right and left sides of the heart and supplies both the body and the lungs.
The defect is virtually always accompanied by a large hole between the two lower pumping chambers, known as a ventricular septal defect (VSD). This VSD allows oxygen-rich blood from the left ventricle and oxygen-poor blood from the right ventricle to mix completely before entering the single truncal vessel. The resulting mixed, partially desaturated blood is distributed to the body, reducing the oxygen supply to vital organs. Furthermore, the single vessel structure causes excessive blood flow into the lungs, leading to high pressure and fluid buildup.
The precise cause of truncus arteriosus is often unknown, but it occurs when the single embryonic outflow tract fails to divide into the aorta and the pulmonary artery during fetal development. Genetic factors are implicated in some cases, particularly the 22q11.2 deletion, commonly known as DiGeorge syndrome. This chromosomal microdeletion is known to affect the development of the heart’s outflow tracts.
Environmental factors during pregnancy may also contribute to the risk, including certain viral illnesses like rubella, uncontrolled maternal diabetes, and exposure to specific teratogens. However, in the majority of children diagnosed with TA, no clear cause is identified.
Recognizing the Signs in Newborns
The clinical signs of truncus arteriosus typically become apparent within the first few days or weeks of life as the newborn’s circulatory system adjusts. One noticeable sign is cyanosis, a bluish or grayish tint to the skin, lips, or nail beds, resulting from insufficient oxygen saturation in the blood. This lack of oxygenation also contributes to extreme sleepiness and lethargy in the infant.
Other symptoms reflect the development of congestive heart failure, which occurs because the heart works excessively hard to manage the high blood flow to the lungs. Infants may exhibit rapid or labored breathing, often accompanied by profuse sweating, particularly during feeding. Poor feeding is common, as the effort of sucking can be exhausting, leading to poor weight gain and failure to thrive.
A healthcare provider listening with a stethoscope will often detect a heart murmur, an abnormal sound caused by the turbulent blood flow through the single large vessel and the VSD. These clinical presentations prompt immediate concern and necessitate specialized medical investigation. The combination of heart failure symptoms and lack of oxygen makes TA a medical emergency requiring prompt diagnosis and surgical planning.
Medical Confirmation Through Diagnosis
The definitive diagnosis of truncus arteriosus relies on specialized imaging techniques that allow cardiologists to visualize the heart’s anatomy and function. The primary diagnostic tool is the echocardiogram, which uses sound waves to create detailed, moving pictures of the heart chambers, valves, and blood vessels. This non-invasive test clearly shows the single great artery leaving the heart and the associated ventricular septal defect, confirming the diagnosis.
Other non-invasive tests provide supporting information about the condition’s severity and its effect on the body. A pulse oximetry reading, using a sensor placed on the skin, quickly measures the level of oxygen saturation in the baby’s blood. A chest X-ray can reveal an enlarged heart shadow (cardiomegaly) and may also show increased blood flow and fluid congestion in the lungs.
An electrocardiogram (EKG) records the electrical activity of the heart, indicating if the heart muscle is under strain or if there are irregularities in the heart rhythm. Together, these diagnostic procedures allow the medical team to fully characterize the defect and plan the necessary surgical intervention.
Surgical Repair and Long-Term Outlook
Surgical correction is mandatory for truncus arteriosus and is typically performed within the first few weeks of life to prevent irreversible damage to the lung blood vessels from excessive blood flow. The complex open-heart procedure, often called the Rastelli repair, aims to establish a normal two-vessel circulation pattern. First, the surgeon closes the large ventricular septal defect using a patch, effectively separating the left and right ventricles.
Next, the pulmonary arteries are disconnected from the single common vessel. The final step involves creating a new connection between the right ventricle and the separated pulmonary arteries using a tube-like graft, known as a conduit. This conduit serves as the new pulmonary artery, ensuring oxygen-poor blood from the right ventricle goes only to the lungs. The single truncal vessel is then left to function as the aorta, carrying oxygenated blood from the left ventricle to the rest of the body.
Following the initial surgery, patients require lifelong, specialized follow-up care with a congenital cardiologist. Truncus arteriosus is not cured by the first operation; the long-term outlook involves managing potential complications and the need for future procedures. The surgically placed right ventricle-to-pulmonary artery conduit does not grow with the child. Over time, it can become narrowed, blocked, or too small for the growing patient.
Because the conduit does not grow, children with repaired TA will require repeat surgeries or catheter-based interventions to replace it multiple times throughout their lives, sometimes every few years in early childhood. Other long-term concerns involve the truncal valve, which now serves as the aortic valve. It can become leaky or narrowed, requiring repair or replacement later in life. Ongoing monitoring is also necessary for heart rhythm disturbances (arrhythmias), a known risk following complex congenital heart surgery.