Persistent Truncus Arteriosus
- Truncus Arteriosus is a defect characterized by the presence of a single arterial vessel that originates overriding a large ventricular septal defect, with two distinct ventricles. This proximal ascending vessel is the source of blood supply to both the systemic, pulmonary, and coronary circulations.
- The truncus arteriosus defect occurs due to failure in developmental septation of the truncus arteriosus outflow tract by the conotruncal ridges and aortopulmonary septum into ascending aorta and pulmonary trunk. This failure leaves a single trunk overriding the ventricles and a larger ventricular septal defect.
- The pulmonary arteries most often arise from a short vessel branching off the common arterial trunk nearby the valve.
- Associated defects include deformities and often incompetencies of the truncal valve, an interrupted aortic arch, and coronary artery anomalies.
- Van Praagh has defined four subtypes of persistent truncus arteriosus:
- Type A1 which consists of a single arterial trunk originating from a common semilunar valve and immediate bifurcation into ascending aorta and pulmonary artery.
- Type A2 which is characterized by both a right and left pulmonary artery that originate from the posterior aspect of the common truncus arteriosus.
- Type A3 is similar to Type A2 but with a larger distance between the origination of the right and left pulmonary arteries from the truncal artery.
- Type A4 is also referred to as pseudotruncus and may be better classified as a form of pulmonary atresia with ventriculoseptal defect rather than persistent truncus arteriosus. This defect occurs when the main pulmonary artery is absent and the lungs receive their blood supply via pulmonary collaterals.
- In the absence of pulmonary stenosis, the presence of a common arterial trunk supplying both the pulmonary and systemic circulations results in pulmonary arterial pressure equal to that in the truncus itself. As a result, the reduction in pulmonary resistence that occurs after birth is not well tolerated. Increased pulmonary blood flow can lead to flooding of the lungs and early pulmonary vascular obstructive disease. Combined with truncal regurgitation which is present in most cases of persistent truncus arteriosus, many infants develop congestive heart failure within the neonatal period.
- Surgical correction of these defects is typically performed within days of diagnosis, due to the high prevalence of heart failure and pulmonary vascular obstructive disease which will present early in life.