Atrial Septal Defect

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Atrial septal defect (ASD) is a defect in the wall (septum) between the heart's two upper, or collecting, chambers (atria). One chamber is known as an atrium. The septum separates the heart's left and right side. Septal defects are sometimes called a 'hole' in the heart.

It is the third most common heart problem that babies are born with. Many defects in the atrial septum close themselves and cause no problems. Otherwise, they can be closed by keyhole procedure or surgery. Most babies born with a defect in the septum have normal survival.

The heart is complex but (looking at the diagram below) you can see there are basically four chambers inside it. The left and right upper, or collecting, chambers (atria) are roughly on top and the bigger stronger ventricles are on the bottom.

heart with septum

The left and right sides of the heart are divided by a wall - this is called the septum. When it is between the atria, it is called the atrial septum. When it is between the lower, or pumping, chambers (ventricles) it is called the ventricular septum. The septum keeps blood from the right and left sides of the heart from mixing. This is important because the blood in the left atrium comes from the lungs and is full of oxygen while the blood in the right atrium comes from the body having already given up the oxygen. A hole or defect in the septum between the atria allows blood to leak from the side with higher pressure (left atrium) to the side with lower pressure (right atrium). The extra blood coming to the right side of the heart gradually loads and stresses the right side of the heart.

For a full explanation of the structure and function of the heart see separate leaflet called The Heart and Blood Vessels.

An ASD is a defect in the septum between the heart's two upper, or collecting, chambers (atria). The septum is a wall that separates the heart's left and right sides. Septal defects are often referred to as a hole in the heart.

Everyone is born with a natural hole between the collecting chambers of the heart. This hole (opening) is known as the foramen ovale. It is very important in the baby in the womb (the fetus), as it directs oxygen-rich blood from the mother's placenta towards the fetus's brain and heart. After birth this opening is no longer needed and closes itself in most individuals. However, in up to one in five healthy adults a small opening may remain. This is known as a patent foramen ovale (PFO).

The ASD is larger than a PFO and may or may not be in the location of the natural hole.

The heart starts out as a simple tube. It needs to change a lot as your baby develops within the womb (uterus). By the time you are eight weeks pregnant your baby should have four chambers in their heart. The development of the atrial septum is complicated and includes contribution from veins bringing blood to the collecting chambers (atria). If the septal wall has not developed properly by this time, the baby may be born with a gap in the septum between the atria. This is sometimes called a hole in the heart. There may be more than one hole. The size and position of the hole can also vary. Small holes are less likely to cause symptoms and more likely to close.

ASDs usually occur by themselves without any associated birth defects. Sometimes they can occur with other heart problems, or as part of an inherited condition.

Sometimes an ASD may be caused by a different problem such as diabetes in the mother. Occasionally it has been linked to heavy smoking or excessive alcohol intake by the mother during pregnancy.

ASDs are the third most common heart defect that babies can be born with. Out of every 1,000 children born, about eight have a heart defect.  Of these, two or three may have an ASD as part of their heart defect. Isolated ASDs make up to 10% of all heart defects.

Atrial septal defects (ASDs) usually do not cause any problems in childhood. Many defects which are small, close as the child grows. However, the child needs to be under regular follow-up of a heart specialist (cardiologist). If the hole does not close itself then it needs to be closed. In the UK this is usually done at around 4 to 5 years of age.

Large ASDs allow a significant amount of blood to leak from the left collecting chamber of the heart to the right collecting chamber and then into the right pumping chamber. This gradually stretches and damages the right side of the heart. That is why these defects are closed in a planned manner at about 5 years of age.

However, ASDs are not always diagnosed in childhood. Therefore, adults with undiagnosed ASD can present with shortness of breath, especially with exercise. They can also experience a feeling of having a 'thumping' heart (palpitations) because of heart rhythm problems.

Your doctor may hear a murmur and ask a children's specialist (a paediatrician) to have a look. They may ask for a chest X-ray or a special ultrasound of your child's heart. This ultrasound of the heart is known as an echocardiogram and shows the structure of the heart. It will also show where the hole is and how big it is. It will check whether other heart problems are present. These are important when deciding how to help the problem.

Sometimes in older children and adults the echocardiogram may not show the ASD very well. It may be necessary to do transoesophageal echocardiography (TOE). This is an ultrasound of the heart done using a special probe which is inserted into the patient's food pipe through the mouth. Children are usually put to sleep by having general anaesthetic but in adults TOE can be done using local anaesthesia.

Babies and children with small holes just need regular check-ups by a children's heart specialist (paediatric cardiologist). Many of the small holes close on their own. If the hole has not closed by 5 years of age it can be blocked. Most holes can be closed by a keyhole procedure using a small blocking device. The device is inserted through a blood vessel so there is no need for open heart surgery. Some holes, because of their large size or their location, cannot be closed by keyhole procedure. These holes require open heart surgery. All these procedures are done in specialist units dealing with children's heart surgery.

Most children in whom the hole is found during childhood, do very well. In many, the hole closes on its own.

Those in whom the hole is closed (either by keyhole procedure or by open heart surgery) require regular follow-up. However, they usually do not have any problems and lead a normal life with no restriction on their activity.

When the hole is diagnosed late in life, some damage to the heart's pumping ability may have already occurred. These patients sometimes have symptoms such as shortness of breath and the feeling of having a 'thumping' heart (palpitations). Closing the hole usually produces some improvement but some symptoms may persist.

In children in whom the hole closes on its own or is closed during childhood the heart function remains normal.

In adults where the hole is diagnosed and closed late, heart function improves but may not become completely normal.

Original Author:
Dr Anjum Gandhi
Current Version:
Peer Reviewer:
Dr Hayley Willacy
Document ID:
28974 (v1)
Last Checked:
26/01/2015
Next Review:
25/01/2018
The Information Standard - certified member
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