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What Is Atrial Septal Defect?
An atrial septal defect (ASD) is a hole in the wall (septum) that separates the two upper chambers (atria) of the heart. The defect allows blood to flow from one atrium to the other, usually from the left side to the right side. This causes extra blood flow:
- In the right atrium
- In the right ventricle
- To the lungs
Figure A shows the normal anatomy and blood flow of the interior of the heart. Figure B shows a heart with an atrial septal defect, which allows oxygen-rich blood from the left atrium to mix with oxygen-poor blood from the right atrium.
In a normal heart, oxygen-poor (blue) blood returns from the body to the right atrium. From the right atrium, the blue blood flows to the right ventricle—one of the two lower chambers of the heart—and is pumped to the lungs to pick up oxygen. After traveling through the lungs, the blood is now oxygen-rich and red. The red blood returns from the lungs to the left atrium and goes to the left ventricle, where it is pumped to the body. The right and left sides of the heart are normally completely separated by the septum. The septum keeps the blue blood from mixing with the red blood. The later section "How the Heart Works" explains the process in greater detail.
ASD is the second most common congenital heart defect.
- More than 3,000 babies are born with ASD each year in the United States.
- ASD occurs twice as often in girls as in boys.
Effects of Atrial Septal Defect
Over time, the extra blood flow to the right side of the heart and the lungs can cause:
- Enlargement of the right atrium and the right ventricle.
- Right heart overload. The right side of the heart has to work harder to pump extra blood to the lungs, especially as resistance in the pulmonary (PULL-mun-ary) artery increases. Over time, the heart may become overworked, and function may become impaired. This is exceedingly rare with modern methods of diagnosis and treatment.
- Irregular heartbeats or rhythms (arrhythmias). Extra blood flowing into the right atrium through the ASD can cause the atrium to stretch and enlarge. When this occurs, a fast heartbeat can develop with symptoms such as dizziness, fainting, or chest discomfort.
- Stroke. Occasionally a blood clot in a vein or in the right side of the heart can pass through the ASD and enter the blood stream, where it can block an artery supplying the brain and cause a stroke.
- Pulmonary artery hypertension. This is when high blood pressure exists in the arteries that carry blood to the lungs. The extra blood being pumped to the lungs can increase the pressure in the pulmonary arteries. Over time, high pressure can damage the arteries and the small blood vessels in the lungs. They thicken and become stiff, making it harder for blood to flow through them (pulmonary vascular disease).
Usually, most of these effects don’t show up until adulthood, often around age 30 or later. They are rare in infants and children.
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