During which developmental stage are osmium primum ASDs formed?

Osmium primum atrial septal defects (ASDs) are formed during the endocardial cushion development stage. This developmental period involves the formation and fusion of the endocardial cushions, which are structures that play a crucial role in the formation of the heart's septa and valves.

During embryonic development, the heart undergoes a series of complex morphogenetic processes, and the endocardial cushions provide a scaffold that contributes to the partitioning of the cardiac chambers. The osmium primum ASD occurs specifically when there is a failure of fusion between the endocardial cushions and the septum primum, leading to an incomplete closure of the atrial septum. This defect is typically seen in the context of atrioventricular septal defects, where the issues with the endocardial cushions are prominent.

Understanding the critical developmental processes associated with cardiac anatomy helps in grasping the etiology of various congenital heart diseases, including ASDs. Recognizing that osmium primum ASDs arise during this specific phase underscores the significance of proper endocardial cushion development in heart formation.