Persistent truncus arteriosus

Persistent truncus arteriosus (or Patent truncus arteriosus or Common arterial trunk), is a rare form of congenital heart disease that presents at birth. In this condition, the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta. This results in one arterial trunk arising from the heart and providing mixed blood to the coronary arteriespulmonary arteries, and systemic circulation.

Causes

Most of the time, this defect occurs spontaneously. Genetic disorders and teratogens (viruses, metabolic imbalance, and industrial or pharmacological agents) have been associated as possible causes. Up to 50% (varies in studies) of cases are associated with chromosome 22q11 deletions (DiGeorge Syndrome). 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 (fibroblast growth factor 8 and bone morphogenetic protein), transcription factors (T-box, Pax, Nkx2-5, GATA-6, and Forkhead), and gap junction proteins (Connexin). The cardiac neural crest also contributes the smooth muscle of the great arteries.

Anatomical changes

TruncusArteriosus.svg

Anatomical changes associated with this disorder include:

  • single artery arising from the two ventricles which gives rise to both the aortic and pulmonary vessels
  • abnormal truncal valve
  • right-sided aortic arch in about 30% of cases (not shown)
  • large ventricular septal defect
  • pulmonary hypertension
  • complete mixing occurring at a level of the great vessel
  • right-to-left shunting of blood

Diagnosis

  • Cyanosis presents at birth
  • Heart failure may occur within weeks
  • Systolic ejection murmur is heard at the left sternal border
  • Widened pulse pressure
  • Bounding arterial pulses
  • Loud second heart sound
  • Biventricular hypertrophy
  • Cardiomegaly
  • Increased pulmonary vascularity
  • Hypocalcemia (if associated with DiGeorge syndrome)

Classification

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 I: truncus -> one pulmonary artery -> two lateral 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 (truncus arteriosus) and connected to the right ventricle using a tube (a conduit or tunnel). 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.