During cardiac embryology, the aorticopulmonary septum divides the truncus arteriosus in a spiral fashion. Failure of this spiral division leads to which congenital heart defect?

• A Tetralogy of Fallot
• B Persistent truncus arteriosus
• C Total anomalous pulmonary venous return (TAPVR)
• D Transposition of great arteries (D-TGA) ✓

Explanation

The aorticopulmonary (AP) septum divides the truncus arteriosus into the ascending aorta and pulmonary trunk by spiraling 180 degrees. This spiral is responsible for the normal crossing of the aorta and pulmonary artery in the chest. If the AP septum fails to spiral (forms a straight partition instead), the aorta arises anteriorly from the right ventricle and the pulmonary artery arises posteriorly from the left ventricle — D-transposition of great arteries (D-TGA). Persistent truncus arteriosus results from complete failure of the AP septum to form. Tetralogy of Fallot results from anterior malalignment of the AP septum.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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