Pulmonary ductal coarctation and left pulmonary artery interruption

Background In a normal neonatal heart the ductus arteriosus forms the direct continuity of the pulmonary trunk to the descending aorta being the main channel for the prenatal blood flow. The pulmonary arteries originate separately from the pulmonary trunk. In congenital heart malformations with pulmonary stenosis to atresia there is often an abnormal lateral DA to left pulmonary artery connection combined with a localised narrowing (pulmonary ductal coarctation / PDC) or even interruption. We investigated embryonic remodelling and pathogenesis of this area Material and methods Normal development was studied in WntCre reporter mice (E10.0-12.5) for neural crest cells and Nkx2.5 immunostaining for second heart field cells. Data were compared to stage matched human embryos including histopathology of neonatal specimen, and a VEGF120/120 mutant mouse strain developing pulmonary atresia. Results Normal mouse and human embryos showed that, in the early embryo, the mid-pharyngeal endothelial plexus, partly covered by second heart field, connected side-ways to the 6 th pharyngeal arch artery (PAA). The ventral segment of this PAA effectively formed the proximal pulmonary artery. The origin of the cells encasing the endothelial tubes differed significantly. The dorsal 6 th PAA segment (future DA on the left side) was solely surrounded by neural crest cells. The ventral segment had a dual outer lining with neural crest cells laterally and second heart field cells medially, while the distal pulmonary artery was covered by neither of these cells. The asymmetric contribution of second heart field to the future pulmonary trunk on the left side of the aortic sac (so-called pulmonary push) was evident. During remodelling the ventral segment of the 6 th PAA became incorporated into the pulmonary trunk leading to a separate connection of the left and right pulmonary arteries to the latter. The VEGF120/120 embryos showed a severely stunted pulmonary push and later on a variety of vascular anomalies in the DA to pulmonary artery connections. Conclusion Side-way connection of the DA to the left pulmonary artery is a congenital anomaly. The primary problem is a stunted development of the second heart field-derived pulmonary push leading to pulmonary stenosis/atresia and a subsequent lack of proper incorporation of the ventral segment of the 6 th PAA into the aortic sac. Clinically, the aberrant smooth muscle tissue of the DA should be addressed to prohibit development of severe PDC or even interruption of the left pulmonary artery.