Atrioventricular Septal Defect

Anatomy & Physiology

In the the partial AVSD there is no ventricular component. The atrial defect is in the inferior portion of the atrial septum. Physiologically it is similar to a secundum ASD. The complete AVSD has a large ventricular component and so physiologically behaves as a large VSD.

In an AVSD the valve arrangement is disturbed. In the partial form there are still 2 valve orifices as the anterior & posterior bridging leaflets are fused (arrow) whereas in the complete form there is a single orifice.

Valve morphology

Presentation

The majority of AVSD are present in children with trisomy 21. Those with a large shunt will present with breathless, and failure to thrive tachycardia. They will have tachycardia an active precordium and there may be murmur of left AV valve (“mitral valve”) regurgitation.

If only a small shunt is present then in a PAVSD the second sound is widely split with an ejection systolic flow murmur at the upper left sternal edge. In a CAVSD the P2 is usually loud due to pulmonary hypertension. In both there may be murmur of left AV valve (“mitral valve”) regurgitation.

Investigations

ECG

Both have a superior axis (negative aVF).

PAVSD trace has PRBBB in V₁ whilst CAVSD trace has upright T waves & tall R waves in V₁suggestive of right ventricular hypertrophy.

Chest X-ray

Those with a big shunt will have cardiomegaly and pulmonary plethora. If moderate to severe AV valve regurgitation is also present these features are exacerbated and pulmonary venous congestion may also be seen.

Small shunts have a normal heart size.

When pulmonary vascular disease is present then there may be large central pulmonary arteries and reduced peripheral pulmonary vasculature

Echocardiogram

This can beautifully demonstrate the anatomy. Showing not only the septal defect but the valve morphology too.

Colour Doppler shows the AV valve regurgitation which in the picture on the right is arrowed as LAVVR (left atrioventricular valve regurgitation) - this is sometimes also referred to as mitral regurgitation but strictly speaking there are no mitral and tricuspid valves hence the rather cumbersome terminology.

Natural History

The PAVSD is haemodynamically similar to an ASD and the natural history is thus similar unless there is significant valve regurgitation in which case heart failure intervenes earlier. A CAVSD behaves as a large VSD and so if not operated upon irreversible vascular disease will develop.

Management

Device closure of these defect is not an option due to the derangement of the normal AV valves. Open heart surgery is thus the only option.

PAVSD

The management is as for a secundum ASD with closure undertaken before the child goes to school.

CAVSD

This defect usually has pulmonary hypertension due to the large VSD. Timing of surgery is therefore before this becomes irreversible. Most surgeons now prefer to operate between 3-6 months of age. The hole is closed with a Dacron patch and two valves fashioned from the common valve.

Prognosis

PAVSD

The operative mortality is approximately 1% and the long term outcome excellent unless there is significant LAVVR which may require further valve repair or replacement.

CAVSD

The operative mortality is higher than for a PAVSD but still around 5%. The necessity for re-operations upon the AV valves is also significantly higher.

This page was last edited 16/2/2004

Acknowledgements