An atrioventricular septal defect (AVSD), also called an AV canal defect or atrioventricular canal defect, is a congenital heart condition in which there is a hole in both the atrial septum (between the upper chambers) and the ventricular septum (between the lower chambers), combined with abnormalities of the mitral and tricuspid valves, which may form a single common atrioventricular valve opening. The condition encompasses a complete form (all components present) and a partial form (affecting mainly the atrial component).
In a complete AVSD, blood can pass freely between all four heart chambers, producing a large left-to-right shunt that overloads the pulmonary circulation. This leads to pulmonary hypertension, breathlessness, poor feeding, and failure to thrive in infancy. AVSD is particularly associated with Down syndrome (trisomy 21): around 40% of children with Down syndrome have congenital heart disease, and AVSD is the most common defect found in this group.
Surgical repair of complete AVSD is typically performed in the first 3 to 6 months of life, before irreversible pulmonary vascular disease develops. The repair closes both septal components with a patch and reconstructs the mitral and tricuspid valves. Outcomes have improved markedly over the past four decades and the majority of children now survive to adulthood.
Adults with repaired AVSD may have residual mitral valve regurgitation, atrial fibrillation, or other arrhythmias, and are followed up in adult congenital heart disease (ACHD) specialist services. Some require reoperation for valve dysfunction in adulthood.