The morphology and diagnosis of atrioventricular septal defects

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Abstract
Summary In this review, we discuss and describe those features which distinguish hearts with abnormal atrioventricular septation from the normal heart. The hearts, best described as atrioventricular septal defects, are unified by having a common atrioventricular junction guarded by a valve having five leaflets. The left component has three leaflets and cannot be interpreted in terms of a cleft in a normal mitral valve. The papillary muscles supporting this valve are also markedly dissimilar from the arrangement seen in normal hearts. The subaortic outflow tract is displaced superiorly compared to the normal heart, and is no longer wedged between the left valve and the septum. There is marked discrepancy in the inlet and outlet lengths of the ventricular mass, these dimensions being equal in hearts with normal atrioventricular septation. Although having the above features in common, atrioventricular septal defects show anatomic variations related to the arrangement of the bridging leaflets and their relationship to the septal structures. There may be a common valvar orifice or separate right and left orifices. The anatomic potential for shunting may be at atrial or ventricular levels, or both. Rarely, the septal structures may be intact. Other important features include ventricular dominance, the left ventricular outflow tract, and the disposition of the atrioventricular conduction tissues.