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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.
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.
Half of all ASDs close without treatment. When treatment is necessary, it
is usually successful. Once the defect has closed or has been repaired, most
children:
- Don’t need additional treatment or medicine
- Can live normal, healthy lives
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 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.
Characteristics
An ASD is classified by its size and location.
Size
The size of an ASD can range from small to large.
- Most small defects close on their own as the heart grows during
childhood. They usually allow only a small amount of blood to flow between
the atria.
- Moderate to large defects are much less likely to close on their own.
They allow two or more times the normal amount of blood to flow through
the right side of the heart. Large holes sometimes cause symptoms during
infancy or childhood.
Location
Three major types of ASD exist, based on the location of the defect on the
septum:
- Secundum. This defect is in the middle of the septum.
It is the most common form of ASD. About 7 out of every 10 babies born
with ASD have this type. This type often closes on its own, unless it is
large.
- Primum. This defect is in the lower part of the septum.
It also involves an incomplete or partial atrioventricular septal defect,
and the valves that separate the upper and lower heart chambers are not
normal. About 2 out of every 10 babies born with ASD have primum defects.
This type of defect does not close on its own.
- Sinus venosus. This defect is in the upper part of the
septum near where a large vein (the superior vena cava) brings blue blood
from the upper body to the right atrium. It is rare, accounting for only
about 1 out of every 10 cases of ASD. Children with sinus venosus defects
usually have an associated condition called partial anomalous pulmonary
venous return, in which one or more of the veins carrying red blood from
the lungs return to the wrong chamber of the heart. This type of defect
does not close on its own.
Symptoms
The major signs and symptoms of atrial septal defect (ASD) are:
- Heart murmur
- Change in heart sounds that represent valve closure
A heart
murmur is the most common sign of ASD. Often, it is the only sign.
Sometimes, the heart murmur is the sound from a delay in the closing of the
pulmonary valve.
Most children with ASD don't have symptoms, even with a large ASD. However,
some children and adults with ASD may develop symptoms which include:
- Fatigue or tiring easily
- Shortness of breath
- Fast breathing
- Sweating
- Slow growth
In most people with ASD who develop symptoms, the symptoms don’t develop
until adulthood.
Diagnosis
Atrial septal defect (ASD) is diagnosed using a medical history, a physical
exam, and tests. ASD is usually found in infants or children during a routine
physical exam. However, some people with ASD are not diagnosed until
adulthood.
Medical and Family History
Your child's doctor will ask you about:
- Family history of congenital heart disease
- Your child's symptoms
- Your child's feeding and growth
Physical Examination
The doctor will listen to your child's heart with a stethoscope for a heart
murmur. The doctor will also check for signs of increased blood flow to the
lungs.
Tests
Your child's doctor may order one or more tests to diagnose ASD. These
tests also help the doctor decide the type and size of the defect:
- Echocardiogram. This test, which is harmless and
painless, uses sound waves to create a moving picture of your child's
heart. During an echocardiogram,
reflected sound waves outline the heart's structure completely. The test
allows the doctor to clearly see any problem with the way the heart is
formed or the way it's working. An echocardiogram is the most important
test available to your child's cardiologist to both diagnose a heart
problem and follow the problem over time. In children with ASD, the
echocardiogram shows exactly where the hole is located in the wall between
the two upper chambers of the heart, how big the hole is, and how the
heart is responding to the defect. The test will also help your child's
cardiologist to know if and when the hole should be closed.
- Chest x ray. It takes a picture of the heart and lungs. It can show if the heart
is enlarged or if there is fluid in the lungs.
- EKG (electrocardiogram). An EKG
test measures the rate and regularity of your child's heartbeat. It
provides an estimate of enlargement of the heart chambers and shows
abnormal heart rhythms (arrhythmias).
- Cardiac catheterization. A thin flexible tube (catheter) is passed through a
blood vessel (artery or vein) to the heart. With the assistance of x rays,
the doctor can see the child's blood vessels and heart. During the
procedure, the doctor can measure blood pressure in the heart and arteries
connected to the heart and see how much blood is mixing between the two
sides of the heart. Cardiac catheterization is rarely used for diagnosis
of ASD, unless the echocardiogram does not provide enough information or
if other defects or problems are suspected.
Causes
There is no single, known cause of atrial septal defect. Heredity (genetics) may play a role in
ASD. The following genes are associated with the disease: ASD1,
ASD3,
NKX2-5,
and GATA4.
Reference:
National Heart, Lung, and Blood Institute, USA.
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