Anatomically Corrected Malposition of the Great Arteries

Abstract

Anatomically corrected malposition (ACM) of the great arteries is a rare anomaly of the conotruncus (infundibulum and great arteries) and of the ventricles. Although very malpositioned, the great arteries nonetheless arise above the morphologically appropriate ventricles, aorta (Ao) above the morphologically left ventricle (LV), and pulmonary artery (PA) above the morphologically right ventricle (RV). How is this possible? Because the ventricles loop in one direction, and the great arteries twist in the opposite direction. For example, the ventricles loop in one direction, say to the right, forming a ventricular D-loop, and the infundibuloarterial cardiovascular segment twists to the left, resulting in L-malposition of the great arteries. This is how the commonest form of ACM is formed; the resulting segmental anatomy is situs solitus of the viscera and atria, D-loop ventricles, and L-malposition of the great arteries, i.e., ACM {S,D,L}. There is atrioventricular (AV) concordance and ventriculoarterial (VA) concordance (but very different from normally related great arteries). Although there is always VA concordance in ACM, by definition, there can be AV discordance, as for example in ACM {S,L,D} and in ACM {I,D,L}. In terms of segmental anatomy, there are six anatomic types of ACM. Associated malformation are often clinically, hemodynamically, and surgically important. Surgical repair of ACM is rarely reported, with some publications limited to the repair of associated lesions in the {S,D,L} form with atrio-ventricular concordance. In the presence of AV discordance ({S,L,D} and {I,D,L}), the condition presents with a transposition physiology. It could be anatomically and physiologically corrected by an atrial switch operation undertaken in the first month of life, or later following LV retraining. A Senning or a Mustard procedure could be considered and would be challenging because of the frequent association of left juxtaposition of the atrial appendages.