An atrioventricular septal defect (AVSD), also called an atrioventricular canal defect or endocardial cushion defect, is a congenital heart condition in which there is a defect involving both the atrial septum (the wall between the upper chambers) and the ventricular septum (the wall between the lower chambers), combined with abnormality of the mitral and tricuspid valves. In a complete AVSD, the four chambers of the heart share a common central opening, and there is a single large atrioventricular valve instead of two separate ones. Partial and intermediate forms also exist, depending on the extent of the septal deficiency and valve involvement.
AVSD is strongly associated with Down syndrome (trisomy 21): approximately 40 to 50 percent of children born with Down syndrome have a congenital heart defect, and of those, AVSD is the most common. Other chromosomal abnormalities and syndromes are also associated with AVSD, though it can also occur in isolation. The condition causes a large left-to-right shunt (blood crossing from the higher-pressure left side to the right), increasing pulmonary blood flow, and atrioventricular valve regurgitation, which together place a significant burden on the heart and lungs from early infancy.
Without surgical repair, the combination of high pulmonary blood flow and valve regurgitation leads to progressive pulmonary hypertension, heart failure and, ultimately, reversal of the shunt (Eisenmenger syndrome), at which point surgery is no longer possible. Surgical repair is therefore recommended in the first six months of life for most children with complete AVSD. The operation involves patch closure of the septal defects and reconstruction of the valves using pericardial tissue. Outcomes from surgical repair are excellent at specialist centres.
For adults with repaired AVSD, long-term follow-up in adult congenital heart disease (ACHD) services is essential. Residual mitral valve regurgitation is the most common long-term issue and may eventually require further intervention. Arrhythmias, particularly atrial fibrillation and other atrial arrhythmias, are also more common in people with repaired AVSD as they age, and carry implications for both symptom management and risk of cardiac arrest.