Atrioventricular Septal Defects
In normal heart, the real atrioventricular septum separates the morphological right atrium from the anatomic left ventricle. It has two portions; the anterosuperior is membranous and the posteroinferior is muscular. The latter is located between the mitral annulus and the tricuspid annulus. The peripheral atrioventricular junction is constituted by an extension of epicardial fat between the walls of atria and ventricles. In atrioventricular septal defect (AVSD) which is due to deficiency of myocardial tissue at AV junction, the membranous septum is absent and there is also a deficiency in the perimembranous muscular tissue. AVSD has received numerous designations in the past including endocardial cushion defect, persistent embryonic atrioventricular canal, atrioventricular canal defect, and ostium primum atrial septal defect. Defect of the endocardial atrioventricular cushions is a nonspecific designation since it can include the absence of right atrioventricular connection and double inlet left ventricle.
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