Most of the time, this defect occurs spontaneously. Genetic disorders, and teratogens have been associated as possible causes. Up to 50% of cases are associated with chromosome 22q11 deletions. The neural crest, specifically a population known as the cardiac neural crest, directly contributes to the aorticopulmonary septum. Microablation of the cardiac neural crest in developing chick embryos and genetic anomalies affecting this population of cells in rodents results in persistent truncus arteriosus. Numerous perturbations affecting the cardiac neural crest have been associated with persistent truncus arteriosus, some of which include growth factors, transcription factors, and gap junction proteins. The cardiac neural crest also contributes the smooth muscle of the great arteries.
Pathophysiology
Anatomical changes associated with this disorder includes:
The most well-known classification was the fourfold system developed by Collett and Edwards in 1949. Collett/Edwards Types I, II, and III are distinguished by the branching pattern of the pulmonary arteries:
Type II: truncus -> two posterior/posterolateral pulmonary arteries
Type III: truncus -> two lateral pulmonary arteries
The "Type IV" proposed in 1949 is no longer considered a form of PTA by most modern sources. Another well-known classification was defined by Van Praaghs in 1965.
Treatment
Treatment is with neonatal surgical repair, with the objective of restoring a normal pattern of blood flow. The surgery is open heart, and the patient will be placed on cardiopulmonary bypass to allow the surgeon to work on a still heart. The heart is opened and the ventricular septal defect is closed with a patch. The pulmonary arteries are then detached from the common artery and connected to the right ventricle using a tube. The common artery, now separated from the pulmonary circulation, functions as the aorta with the truncal valve operating as the aortic valve. Most babies survive this surgical repair, but may require further surgery as they grow up. For example, the conduit does not grow with the child and may need to be replaced as the child grows. Furthermore, the truncal valve is often abnormal and may require future surgery to improve its function. There have been cases where the condition has been diagnosed at birth and surgical intervention is an option. A number of these cases have survived well into adulthood.
Epidemiology
Persistent truncus arteriosus is a rare cardiac abnormality that has a prevalence of less than 1%.
