Atrial septal defect (ASD) is a hole (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. A septal defect is sometime 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.
Understanding the heart
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.
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.
What is an atrial septal defect?
An atrial septal defect (ASD) is a hole (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. A septal defect is 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 while the baby (fetus) is in the womb (uterus) as it directs oxygen-rich blood from the mother’s placenta towards the baby’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 same place as the natural hole.
Why do atrial septal defects happen?
The heart starts out as a simple tube. It needs to change a lot as your baby develops within the womb (uterus). By the eighth week of pregnancy the 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.
How common is an atrial septal defect?
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.
What are the problems with an atrial septal defect?
ASDs usually do not cause any problems in childhood. Many defects which are small will 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 4-5 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.
How is an atrial septal defect diagnosed?
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 (echocardiogram, or ‘echo’) 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 food pipe (oesophagus) through the mouth. Children are usually put to sleep by having general anaesthetic but in adults TOE can be done using local anaesthesia and medicine to cause drowsiness (sedation).
What can be done to help?
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 closed.
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.
What is the outlook?
Most children in whom the hole is found during childhood do very well. In many, the hole closes on its own. If the hole closes on its own or is closed during childhood then the function of the heart usually remains normal.
If the hole is not closed (either by keyhole procedure or by open heart surgery) then regular follow-up is needed. However, there are usually no problems and the person can lead a normal life with no restriction of activity.
When the hole is diagnosed late in life, there may have been some damage to the heart’s pumping ability. Then there may be some 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.