Truncus arteriosus (TA) is a rare, complex congenital heart defect present at birth. This critical condition results from an error in early fetal development where a single large blood vessel, known as the truncus, fails to divide completely into the aorta and the pulmonary artery. This failure creates a life-threatening circulatory imbalance, requiring immediate medical intervention.
The Structural Anomaly and Blood Flow Disruption
The defining feature of truncus arteriosus is a single great artery exiting the heart’s ventricles, overriding both the left and right pumping chambers. Instead of the normal separate aorta and pulmonary artery, only one vessel exists. Nearly all infants with TA also have a large hole between the two lower chambers, known as a ventricular septal defect (VSD).
The VSD allows oxygen-poor blood from the right ventricle and oxygen-rich blood from the left ventricle to mix freely before entering the common arterial trunk. The pulmonary arteries branch directly off this single vessel. Consequently, all blood leaving the heart is a mixture, significantly reducing the overall oxygen saturation delivered to the body.
The physiological disruption is severe because the single vessel supplies blood to both the body and the lungs simultaneously. Since lung vessels offer less resistance than systemic vessels, a disproportionately large amount of blood flows into the pulmonary circulation. This excessive flow overloads the lung’s vascular bed, leading to pulmonary hypertension and causing the heart to work much harder.
This massive, high-pressure blood flow damages the pulmonary arteries over time. Without prompt surgical correction, these vessels can become permanently scarred and narrowed. The resulting systemic circulation imbalance and heart strain are why the condition is medically urgent in the first days and weeks of life. The heart must pump significantly more volume to compensate for the inefficiency of the mixed circulation.
Identifying Signs and Diagnostic Procedures
The signs of truncus arteriosus usually become apparent within the first few days after birth as the newborn’s circulatory system transitions. A common sign is cyanosis, a bluish tint to the skin, lips, and nail beds, resulting from the lower oxygen level in the circulating blood. Infants may also exhibit profound fatigue or excessive sleepiness due to poor oxygen delivery.
Other noticeable symptoms relate to the heart’s struggle to manage circulatory overload, often manifesting as signs of congestive heart failure. These include rapid or heavy breathing, profuse sweating—particularly during feeding—and a disinterest in eating, leading to poor weight gain. A physician listening with a stethoscope typically hears a heart murmur, caused by turbulent blood flow through the single vessel and the VSD.
Diagnosis often begins with pulse oximetry, a non-invasive screening test that measures blood oxygen saturation and indicates abnormally low levels. The definitive diagnostic tool is the echocardiogram (echo), an ultrasound that provides detailed images of the heart’s structure and blood flow patterns. The echo clearly visualizes the single arterial trunk exiting the heart and confirms the size and location of the VSD.
Supporting tests assess the full impact of the defect on the cardiovascular and pulmonary systems. A chest X-ray shows the size and shape of the heart, which is often enlarged, and may reveal fluid buildup in the lungs due to excessive blood flow. An electrocardiogram (EKG) records the heart’s electrical activity, indicating strain or enlargement of the ventricles.
Surgical Correction and Immediate Management
Repairing truncus arteriosus requires open-heart surgery, typically performed within the first few weeks of life to prevent irreversible damage to the lung vessels from pulmonary hypertension. Immediate management involves stabilizing the infant with medications, such as diuretics, to reduce fluid buildup and manage congestive heart failure. High-calorie feedings may also be necessary to help the infant gain strength for the procedure.
The surgical procedure, sometimes called a Rastelli-type repair, establishes two separate, functional circulatory pathways. The surgeon first closes the VSD with a patch, effectively separating the left and right ventricles. This ensures that oxygen-poor and oxygen-rich blood no longer mix.
The next steps involve creating a new pulmonary artery. The pulmonary arteries are detached from the common truncus, and the common vessel is repurposed to serve as the new aorta, routing oxygen-rich blood to the body. A valved conduit (a tube containing a valve) is then placed to connect the right ventricle to the newly detached pulmonary arteries.
This conduit provides a dedicated outflow tract to carry oxygen-poor blood from the right ventricle directly to the lungs, completing the separation of the two circulatory systems. Following the repair, the infant is moved to an intensive care unit. Post-operative care focuses on managing the heart and lungs, often requiring temporary mechanical ventilation and medications to control blood pressure and heart function.
Long-Term Monitoring and Quality of Life
The initial surgical repair is reconstructive and life-saving, but it is not a complete cure, necessitating lifelong specialized cardiac care. The primary long-term challenge is the durability of the artificial conduit placed between the right ventricle and the pulmonary artery. Since the conduit does not grow with the child, it will inevitably become too small or experience wear, such as stenosis (narrowing) or regurgitation (leaking).
These issues require continuous monitoring and often lead to future reoperations to replace the conduit. Many patients undergo multiple replacements before reaching adulthood. Reintervention can also arise from problems with the truncal valve, which serves as the aortic valve after repair and may become leaky over time.
Despite the high likelihood of reoperation, the long-term prognosis is generally positive, with survival rates extending well into adulthood for most patients. Individuals who have undergone successful TA repair typically lead active lives, though some may experience reduced exercise tolerance compared to their peers. Continuous follow-up with a cardiologist specializing in adult congenital heart disease is necessary to monitor heart function and plan for required interventions or surgical procedures.