Atrioventricular septal defect (AVSD)

What is atrioventricular septal defect?

You may also hear atrioventricular septal defect called atrioventricular canal (AV canal) defect or endocardial cushion defect.

In a normal heart, there are four chambers. Two pumping chambers (ventricles) and two collecting chambers (atria). The ventricles and atria are separated by the AV valves known as the tricuspid valve and the mitral valve.

The ventricles and atria are also separated by a wall called a septum. The ventricular septum separates the right and left ventricles, and the atrial septum separates the right and left atria. This means that the blood in the right ventricle doesn’t mix with the blood in the left ventricle.

There is a natural hole in the septum of the atria called a foramen ovale. This is there during pregnancy and once the baby is born this should close spontaneously.

An atrioventricular septal defect (AVSD) is a where there are holes in the walls (septum) dividing the left and right chambers of the heart, and the AV valves that separate the ventricles and atria may not be formed correctly. Instead of there being two separate AV valves, there is a common valve which has failed to separate.

Because of the holes between the ventricles and atria, the blood flows where it should not normally go. The holes allow more blood to flow to the lungs, and this can make the right side of the heart work harder.

The incidence of AVSD is around 1:5000 and this condition is associated with Down’s Syndrome (Trisomy 21).

There are three different types of AVSD:

• Complete AVSD (CAVSD): This defect is the most common and there is a hole in the ventricular septum, a hole in the atrial septum and a common valve. This common valve has leaflets that may not have formed correctly or close tightly.

• Partial AVSD (PAVSD):  This defect has some, but not all of the defects of a complete AVSD. There is usually a hole in the atrial wall or in the ventricular wall near the centre of the heart. A partial AVSD usually has two AV valves, but one of the valves (usually mitral) may not close completely and this allows blood to leak backward from the left ventricle into the left atrium. This is the second most common type.

• Unbalanced AVSD: This defect describes an AVSD where the common valve is not placed equally over both ventricles. This unbalance leads to a reduction of blood flow into the one of the ventricles causing the ventricle to be hypoplastic.

For more information regarding treatment of unbalanced AVSD please see the single ventricle defect information.

1. Inlet ventricular septal defect
2. Ostium primum defect (ASD Type I)
3. Left AV-Valve cleft
4. Right AV-Valve cleft

How can atrioventricular septal defect be spotted?

An AVSD can be detected at the 20 week anatomy scan or after birth by echocardiogram.

If the AVSD is not picked up in the antenatal period, once the baby is born it will display the following signs:

• Increase in the rate and effort of breathing
• Difficulty feeding
• Lethargy (sleepy)
• Sometimes can have lower than normal oxygen levels
• Heart murmur

How can atrioventricular septal defect be treated?

Babies with AVSD will require open heart surgery. In most cases, the babies will be able to go home after birth and attend regular clinic appointments until they are ready for their surgery.

They can be more susceptible to infection and sometimes need to spend some time as an inpatient in hospital if they have symptoms that require medical/nursing intervention.

CAVSD – if baby has lots of symptoms and the medical management is not helping, then a pulmonary artery banding may be considered. This is heart surgery, but not on bypass and involves a ligature tied around the pulmonary artery to restrict the blood flow. The baby would then still require open heart surgery to repair the AVSD – usually at the original planned time.

AVSD requires open heart surgery to repair the condition. The timing of this can vary between centres throughout the UK.

CAVSD is usually repaired at about 4 months of age.

PAVSD is usually repaired at about 12-18 months of age.

Open heart surgeries are performed under general anaesthetic, the timing of which will depend on the severity of the anomaly, and the general condition of the baby.

Common symptoms

Poor feeding: Where babies can’t take a full feed because they are breathless/tired. This can lead to poor weight gain and could require tube feeds and/or high calorie milk. Sometimes babies can have combination feeding – which can be breast feeding or bottle feeding with some ‘top ups’ via the tube so they can still enjoy feeding as much as possible.

Sub-optimal cardiac function: Where the heart is not working as efficiently as it should be because the heart valve is leaking. This can be managed by introducing diuretics (‘water’ medicines) to help the lungs expel the extra fluid and then baby should be able to breathe more easily, feed better and put weight on. Sometimes the symptoms persist and the frequency/dose of the diuretics needs to be reviewed. Sometimes another medication could be used in addition to the diuretics, to help if baby still has symptoms – this is called an ACE inhibitor. The team looking after baby will discuss the therapy required.

General advice/info for the future

Babies and children with an AVSD will need lifelong follow-up. The aim of these check-ups is to monitor your child’s heart function so that any future heart problems are diagnosed and treated quickly. In a small number of cases, children with CAVSD can require further intervention on the heart valves. There is also a small chance left ventricular outflow tract obstruction (LVOTO) can occur, which would also require intervention.

Your cardiologist will advise you about any restrictions on activity that you should be aware of, but generally children are able to do all the usual childhood activities.

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