STRUCTURAL HEART DISEASE (RJ SIEGEL AND NC WUNDERLICH, SECTION EDITORS) Atrioventricular Septal Defects: Pathology, Imaging, and Treatment Options Anas S. Taqatqa 1,2 & Joseph J. Vettukattil 1,2,3 Accepted: 14 May 2021 # The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021 Abstract Purpose of Review Atrioventricular septal defects (AVSD) represent a broad spectrum of congenital anomalies from simple to the most complex heart defects including some distinct types. Clinical presentation and timing of intervention differ by mor- phological subset and functional anatomy. Herein, we review morphological variations and characteristics that determine appro- priate intervention and provide insights into functional anatomy based on detailed three-dimensional (3D) assessment of AVSDs. Recent Findings The understanding of functional morphology of AVSDs has improved significantly with detailed 3D echocar- diographic evaluation of the atrioventricular junction and valve morphology. As prenatal detection of AVSDs has increased significantly, it has become the most common fetal cardiac diagnosis enabling antenatal counseling and delivery planning. Advances in diagnosis and perioperative care have resulted in optimal outcomes. Summary The diagnosis and management of AVSDs have improved over the years with enhanced understanding of anatomy and perioperative care resulting in optimal short and long-term outcomes. Keywords Congenital heart disease . Pediatric . ACHD . Atrioventricular septal defect . Down syndrome Introduction Atrioventricular septal defect (AVSD) also known as atrio- ventricular canal defects, common atrioventricular canal, or endocardial cushion defect comprises various cardiac anoma- lies. The shared findings include common atrioventricular junction and AV valve defects [1••]. AVSDs account for 4– 7% of all congenital heart defects and are commonly observed in patients with Down syndrome [2, 3]. Classifications and Types The valves that guard the atrioventricular junction are normal- ly separated from each other with an independent fibromuscular ring. The aortic valve is wedged between the left and right atrioventricular valve rings (Fig. 1). In AVSDs, the two AV valve rings are fused together to form a common atrioventricular junction with aortic annulus unwedged antero-cephalad causing the classical gooseneck abnormality of the left ventricular outflow tract on imaging, which in turn predisposes patients to subaortic obstruction. Thus, there is no mitral or tricuspid valve in AVSDs, but left and right AV valves with varying characteristic morphology. The spectrum of morphological variation of the common AV valve may be classified for better understanding into the 4 anatomic profiles as defined by the International Pediatric and Congenital Cardiac Code (IPCCC) [4, 5••]. A. The complete AVSD encompasses primum atrial sep- tal defect (ASD), inlet ventricular septal defect (VSD), and common AV valve (Fig. 2). This AV valve has five leaflets: superior bridging leaflet (SBL), inferior bridging leaflet (IBL), left mural (lateral) leaflet, and two right leaflets (antero-superior and inferior). The shunting This article is part of the Topical Collection on Structural Heart Disease * Joseph J. Vettukattil Joseph.Vettukattil@helendevoschildrens.org Anas S. Taqatqa Anas.Taqatqa@spectrumhealth.org 1 Congenital Heart Center, Spectrum Health Helen DeVos Children’s Hospital, Grand Rapids, MI, USA 2 Pediatrics and Human Development, Michigan State University College of Human Medicine, Grand Rapids, MI, USA 3 Congenital Heart Center, Spectrum Health Helen DeVos Children’s Hospital, 100 Michigan NE, Grand Rapids, MI 49503, USA https://doi.org/10.1007/s11886-021-01523-1 / Published online: 1 July 2021 Current Cardiology Reports (2021) 23: 93