Truncus arteriosus (Van Praagh type A4)

Truncus arteriosus is an uncommon congenital cardiac abnormality that occurs due to the failure of conotruncal septation during development of the fetus. It is characterized by a single arterial trunk that originates from the heart and supplies the systemic, pulmonary, and coronary circulation¹.

The original and more popular classification of truncus arteriosus was devised by Collett and Edwards in 1949, which divides this anomaly into four types²:

• Type 1: Common pulmonary artery arising from truncus – 80%
• Type 2: Right and left pulmonary artery arise separately from the posterior part of truncus
• Type 3: Separate origin of the pulmonary arteries from the lateral aspect of the truncus
• Type 4: Neither pulmonary arterial branch arising from the common trunk (pseudo-truncus), is now recognized to be a form of pulmonary atresia with VSD rather than truncus arteriosus.

In 1965, Van Praagh modified the classification system which also includes four primary types³:

• Type A1: Identical to the Type I of Collett and Edwards
• Type A2: Separate origin of the branch pulmonary arteries from the left and right lateral aspects of the common trunk
• Type A3: Origin of one branch pulmonary artery (usually the right) from the common trunk, with other lung supplied either by collaterals or a pulmonary artery arising from the aortic arch
• Type A4: Coexistence of an interrupted aortic arch.