atrioventricular septal defect
An atrioventricular septal defect is a defect at the very center of the heart, where the atrial wall, the ventricular wall, and the two inflow valves should all meet. Picture the crossroads where four chambers come together: if that central junction fails to form, the result is a combined hole spanning both the atrial and ventricular levels, plus a malformation of the valves between them.
Because the deficiency sits where the mitral and tricuspid valves normally separate and anchor, those valves are abnormal too, often forming a single shared valve that leaks. Blood shunts left to right across the central defect and may also leak backward through the faulty valve, so the lungs and heart are doubly burdened, frequently causing heart failure symptoms in infancy.
Atrioventricular septal defects are strongly associated with Down syndrome. Repair is surgical, dividing the central hole back into proper septa and reconstructing two competent valves, ideally within the first months of life before pulmonary pressures rise.
An infant with Down syndrome and heart failure symptoms is found on echocardiography to have a complete atrioventricular septal defect with a single common valve.
A complete atrioventricular septal defect involves a single shared inflow valve.
Because of its strong link with Down syndrome, newborns with that diagnosis are routinely screened with echocardiography to detect an atrioventricular septal defect early.