Atrial Septal Defect
An atrial septal defect (ASD) is a hole in the part of the septum that separates the atria. (The atria are the upper chambers of the heart.)
An ASD allows oxygen-rich blood to flow from the left atrium into the right atrium, instead of flowing into the left ventricle as it should. So, instead of going to the body, the oxygen-rich blood is pumped back to the lungs, where it has just been.
Cross-Section of a Normal Heart and a Heart With an Atrial Septal Defect
Figure A shows the structure and blood flow inside a normal heart. Figure B shows a heart with an atrial septal defect. The hole allows oxygen-rich blood from the left atrium to mix with oxygen-poor blood from the right atrium.
An ASD can be small, medium, or large. Small ASDs allow only a little blood to flow from one atrium to the other. Small ASDs don't affect how the heart works and don't need any special treatment. Many small ASDs close on their own as the heart grows during childhood.
Medium and large ASDs allow more blood to leak from one atrium to the other. They're less likely to close on their own.
Most children who have ASDs have no symptoms, even if they have large ASDs.
The three major types of ASDs are:
- Secundum. This defect is in the middle of the atrial septum and is the most common form of ASD. About 8 out of every 10 babies born with ASDs have secundum defects. At least half of all secundum ASDs close on their own. However, this is less likely if the defect is large.
- Primum. This defect is in the lower part of the atrial septum. Primum defects often occur with heart valve problems. These defects aren't very common, and they don't close on their own.
- Sinus venosus. This defect is in the upper part of the atrial septum. It's close to where a large vein (the superior vena cava) brings oxygen-poor blood from the upper body to the right atrium. Sinus venosus defects are rare, and they don't close on their own.
Atrial Septal Defect Complications
If an ASD isn't repaired, the extra blood flow to the right side of the heart and lungs may cause heart problems. Most of these problems don't occur until adulthood, often around age 30 or later.
Possible complications include:
- Right heart failure. An ASD causes the right side of the heart to work harder because it has to pump extra blood to the lungs. Over time, the heart may become tired from this extra work and not pump well.
- Arrhythmias, extra blood flowing into the right atrium through an ASD can cause the atrium to stretch and enlarge. Over time, this can lead to irregular heartbeats called arrhythmias. Symptoms may include palpitations or a rapid heartbeat.
- Stroke. Usually, the lungs filter out small blood clots that can form on the right side of the heart. Sometimes, though, a blood clot can pass from the right atrium to the left atrium through an ASD and be pumped out to the body. The clot can travel to an artery in the brain, block blood flow, and cause a stroke.
- Pulmonary hypertension (PH). PH is increased pressure in the pulmonary arteries. These arteries carry blood from the heart to the lungs to pick up oxygen. Over time, PH can damage the arteries and small blood vessels in the lungs. They become thick and stiff, making it hard for blood to flow through them.
These problems develop over many years and rarely occur in infants and children. They also are rare in adults because most ASDs close on their own or are repaired in early childhood.