Atrial Septal Defect
An atrial septal defect (ASD) is a hole in the part of the septum that separates the atria (the upper chambers of the heart). This hole allows oxygen-rich blood from the left atrium to flow into the right atrium instead of flowing into the left ventricle as it should.
This means that oxygen-rich blood gets pumped back to the lungs, where it has just been, instead of going to the body.
Figure A shows the normal structure and blood flow in the interior of the 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 or large. Small ASDs allow only a little blood to flow from one atrium to the other. Small ASDs don't affect the way the heart works and don't need any special treatment. Many small ASDs close on their own as the heart grows during childhood.
Medium to large ASDs allow more blood to leak from one atrium to the other, and 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. It's 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. It often occurs along with problems in the heart valves that connect the upper and lower heart chambers. Primum 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, near 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
Over time, if an ASD isn't repaired, the extra blood flow to the right side of the heart and lungs may cause heart problems. Usually, most of these problems don't show up until adulthood, often around age 30 or later. Complications are rare in infants and children.
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 (ah-RITH-me-ahs) - Extra blood flowing into the right atrium through an ASD can cause the atrium to stretch and enlarge. Over time, this can lead to arrhythmias (irregular heartbeats). Arrhythmia 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 a blood clot can pass from the right atrium to the left atrium through an ASD and be pumped out to the body. This type of 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 your heart to your 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 harder for blood to flow through them.
These problems develop over many years and don't occur in children. They also are rare in adults because most ASDs either close on their own or are repaired in early childhood.
Ventricular Septal Defect
A ventricular septal defect (VSD) is a hole in the part of the septum that separates the ventricles (the lower chambers of the heart).
The hole allows oxygen-rich blood to flow from the left ventricle into the right ventricle instead of flowing into the aorta and out to the body as it should.
Figure A shows the normal structure and blood flow in the interior of the heart. Figure B shows two common locations for a ventricular septal defect. The defect allows oxygen-rich blood from the left ventricle to mix with oxygen-poor blood in the right ventricle.
An infant who is born with a VSD may have a single hole or more than one hole in the wall that separates the two ventricles. The defect also may occur by itself or with other congenital heart defects.
Doctors classify VSDs based on the:
- Size of the defect
- Location of the defect
- Number of defects
- Presence or absence of a ventricular septal aneurysm—a thin flap of tissue on the septum. This tissue is harmless and can help a VSD close on its own.
VSDs can be small or large. Small VSDs don't cause problems and often may close on their own. Because small VSDs allow only a small amount of blood to flow between the ventricles, they're sometimes called restrictive VSDs. Small VSDs don't cause any symptoms.
Medium VSDs are less likely to close on their own. They may require surgery to close and may cause symptoms during infancy and childhood.
Large VSDs allow a large amount of blood to flow from the left ventricle to the right ventricle. They're sometimes called nonrestrictive VSDs. A large VSD is less likely to close completely on its own, but it may get smaller over time. Large VSDs often cause symptoms in infants and children, and surgery usually is needed to close them.
VSDs are found in different parts of the septum.
- Membranous VSDs are located near the heart valves. These VSDs can close at any time.
- Muscular VSDs are found in the lower part of the septum. They're surrounded by muscle, and most close on their own during early childhood.
- Inlet VSDs are located close to where blood enters the ventricles. They're less common than membranous and muscular VSDs.
- Outlet VSDs are found in the part of the ventricle where blood leaves the heart. These are the rarest type of VSD.
Ventricular Septal Defect Complications
Over time, if a VSD isn't repaired, it may cause heart problems. A moderate to large VSD can cause:
- Heart failure - Infants who have large VSDs may develop heart failure because the left side of the heart pumps blood into the right ventricle in addition to its normal work of pumping blood to the body. The increased workload on the heart also increases the heart rate and the body's demand for energy.
- Growth failure, especially in infancy - A baby may not be able to eat enough to keep up with his or her body's increased energy demands. As a result, the baby may lose weight or not grow and develop normally.
- Arrhythmias (irregular heartbeats) - The extra blood flowing through the heart can cause areas of the heart to stretch and enlarge. This can disturb the heart's normal electrical activity, leading to arrhythmias.
- PH - The high pressure and high volume of extra blood pumped through a large VSD into the right ventricle and lungs can scar the lung's delicate arteries. Today, PH rarely develops because most large VSDs are repaired in infancy.