Complete Atrioventricular Septal Defect

This is a serious heart abnormality which consists of a complicated hole between the right and left sides of the heart. The hole occurs in the centre of the heart, effectively producing two holes – one between the two small pumping chambers (atriums) and the other between the two main pumping chambers (ventricles). The hole also affects the inlet valves of the heart. Normally there is a separate inlet valve in the right side of the heart (the tricuspid valve) and a separate inlet valve in the left side (the mitral valve). With atrioventricular septal defect (AVSD) the middle part of the two valves is shared between the left and right sides of the heart – often referred to as a bridging leaflet or a common valve. Normally the inlet valves open to let the ventricles fill with blood and then close to allow all the blood to be pumped to the body and the lungs through the main arteries leaving the heart. The abnormality of the inlet valves in AVSD often stops the valves (particularly the mitral valve, on the left side of the heart) closing properly, so it is not watertight when it closes.

An ultrasound scan of the heart (an “echocardiogram”) is required to make the diagnosis, and to watch for any new problems developing as the child grows.

Babies with AVSD usually look perfectly well when they are born, but they gradually become breathless over the first month or so after birth. When this happens medicines can help to some extent, but most babies require major heart surgery to try to repair the defect when they are about 3 months old. The surgery is very complicated because the surgeon has to try to close the 2 holes (using patches of material) at the same time as dividing the common inlet valve into separate right and left parts. The main problem with surgery is that the left sided inlet valve (mitral valve) always leaks to some extent after the holes are closed (this is called mitral regurgitation). If the mitral valve only leaks a little this may not matter and further treatment may never be necessary. However if the mitral valve leaks badly it can be such a serious problem that the baby may die, or that further major surgery is needed to repair or replace the mitral valve. Replacing the mitral valve (a metal valve is normally used) in small babies is a difficult procedure and carries a further risk to the baby‘s life.

Further major surgery is always necessary after valve replacement in babies because they outgrow the valve. The risk of a baby dying at surgery to repair an AVSD will depend to some extent on how well the mitral valve works before the operation, but overall the risk of survival is approximately 97%.

Follow up
It is important for all patients with a repaired AVSD to be seen in the cardiology outpatient department to make sure that mitral regurgitation does not become worse. In addition, a small proportion of children can develop narrowing of the outflow of the left ventricle (subaortic stenosis) after repair of the AVSD. This may need surgical treatment.

General advice for the future
Patients with repaired AVSD can live normal active lives, including all kinds of sport. Most have a normal exercise tolerance but if there is significant mitral regurgitation it is usual to be more breathless than normal on exercise.

All patients with a repaired AVSD will be at risk of infection in the heart (called
endocarditis). Such infections may be caused by infections of the teeth or gums. It is important to have good dental hygiene and to visit the dentist regularly. Ear or body piercing and tattooing are best avoided as they also carry a small risk of infection which may spread to the heart.