Atrioventricular septal defect

Overview & Definition

Picture the four chambers of the heart meeting at a single point — the crux — where the atrial septum, the ventricular septum, and the atrioventricular valves all interlock. In an atrioventricular septal defect, that meeting never happens properly. The endocardial cushions that should fuse to close this junction fail, leaving a single, shared atrioventricular junction that straddles both the atrial and the ventricular septum, with malformed valve leaflets that bridge across the gap. This is why the old names — endocardial cushion defect and atrioventricular canal — still surface in exams, and why the morphology is impossible to understand without holding the crux in your mind. [1]

The definition worth memorising is anatomical and unifying. An AVSD is a congenital heart defect characterised by a deficiency of the atrioventricular septum, a common atrioventricular junction, and a variable arrangement of bridging leaflets that may form one shared valve or two tethered valves. The structural consequences are always a combination of a primum atrial septal defect, an inlet ventricular septal defect, and abnormalities of the left atrioventricular valve, traditionally called a cleft mitral valve. The exact mix of these determines where a patient sits on the spectrum. [1] [2]

The reason this lesion earns a high-yield place in every fellowship curriculum is that it sits at the intersection of anatomy, genetics, and surgical timing. It is the commonest major cardiac lesion in Down syndrome, it is one of the few congenital defects with a signature ECG finding, and it has a hard deadline — repair the complete form early or lose the patient to pulmonary vascular disease. Hold those three threads together, and the rest of the topic falls into place around them. [3] [7]

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1. [1]Craig B Atrioventricular septal defect: from fetus to adult. Heart, 2006.PMID 17105897
2. [2]Calabrò R, Limongelli G Complete atrioventricular canal. Orphanet J Rare Dis, 2006.PMID 16722604
3. [3]Bergström S, Carr H, Petersson G, et al Trends in congenital heart defects in infants with Down syndrome. Pediatrics, 2016.PMID 27252035
4. [4]Pierpont ME, Basson CT, Benson DW Jr, et al. Genetic basis for congenital heart defects: current knowledge: a scientific statement from the American Heart Association. Circulation, 2007.PMID 17519398
5. [5]Pierpont ME, Brueckner M, Chung WK, et al Genetic basis for congenital heart disease: revisited: a scientific statement from the American Heart Association. Circulation, 2018.PMID 30571578
6. [6]Jacobs JP, Jacobs ML, Mavroudis C, et al. Atrioventricular septal defects: lessons learned about patterns of practice and outcomes from the congenital heart surgery database of the society of thoracic surgeons. World J Pediatr Congenit Heart Surg, 2010.PMID 23804725
7. [7]Suzuki K, Yamaki S, Mimori S, et al Pulmonary vascular disease in Down's syndrome with complete atrioventricular septal defect. Am J Cardiol, 2000.PMID 10946038
8. [8]Paladini D, Volpe P, Sglavo G, et al. Partial atrioventricular septal defect in the fetus: diagnostic features and associations. Ultrasound Obstet Gynecol, 2009.PMID 19705406
9. [9]O'Connor M, Stauber CE, Venardos NM, et al. The fate of the left atrioventricular valve after atrioventricular septal defect repair. Pediatr Cardiol, 2026.PMID 40208292
10. [10]Baumgartner H, De Backer J The ESC clinical practice guidelines for the management of adult congenital heart disease. Eur Heart J, 2020.PMID 33128054