An atrial septal defect (ASD) is a type of congenital heart defect in which a hole occurs between the heart’s two upper chambers (atria). Because the pressure is higher on the left of the heart than the right, the hole allows blood to seep from the left atrium to the right atrium. The amount of blood flow shunted from the left side of the heart to the right depends on the size of the hole.

An ASD results in excessive blood flow to the right side of the heart and lungs. The more blood that is diverted to the right side of the heart, the harder the lungs and right ventricle must work to compensate for the problem.

Eventually, the stress on the right ventricle can cause it to enlarge (dilate) to make up for the increased workload. Also, the lungs can become congested upon receiving more blood than is needed, which may lead to high blood pressure in the lungs (pulmonary hypertension). Other problems associated with an ASD include regurgitation of blood into the right atrium, respiratory infections, the formation of blood clots (which could lead to a stroke) and the development of abnormal heart rhythms (arrhythmias). In some rare cases, an untreated ASD can lead to sudden cardiac death.

ASDs may be too small to cause any obvious symptoms, or they may cause symptoms that resemble heart failure in infancy. However treatment may be especially necessary if other defects are present. Non-surgical treatments include medication (e.g., diuretics to flush out excess fluids) or a catheter-based procedure to plug the hole. Surgeries that repair the defect include minimally invasive heart valve surgery and open-heart surgery.

An atrial septal defect (ASD) is a hole in the wall (septum) between the heart’s two upper chambers (atria). The hole may be as small as a pinpoint or as large as the space of the entire septum (i.e., the total absence of the septum). Although this is a form of congenital heart disease (heart defects that are present at birth), it is sometimes goes unnoticed until adulthood, when it begins to cause various symptoms. Most cases of ASD begin to show symptoms by age 30.

No matter when it is noticed, the sooner as ASD is corrected, the better for the patient. Small holes may close on their own in the first years of life without any symptoms or harmful effects. However, they could lead to the production of blood clots that may be carried to the brain and cause a stroke. Larger holes allow more blood to pass through, increasing the risk of symptoms and other harmful effects, including arrhythmias (abnormal heart rhythms).

When an ASD is present, some of the oxygen-rich blood that should travel to the left ventricle from the left atrium is diverted (shunted) through the ASD and into the right atrium, where it mixes with oxygen-poor blood from the rest of the body. The right atrium of the heart is thus receiving blood from two different places: from the veins and from the left atrium (through the ASD). This results in too much blood flow to the right side of the heart and lungs. The more blood that is diverted to the right side of the heart, the harder the lungs and right ventricle must work to compensate.

Eventually, the stress on the right side of the heart  may cause it to enlarge (atrial/ventricular enlargement).  Also, the lungs can become congested from receiving more blood than is needed, which may lead to high blood pressure in the lungs (pulmonary hypertension). This buildup of extra fluid may cause upper respiratory infections and difficulty breathing in the young patient.

Because the blood flows from the left side of the heart to the right, an ASD is known as a type of left-to-right shunt. Left-to-right shunts, which also include ventricular septal defect (VSD) and patent ductus arteriosus (PDA), account for over half of all congenital heart defects. ASD is the most common type of left-to-right shunt.

ASD occurs in three main forms:

• Primum ASDs are located in the lower portion of the atrial septum, and are almost always accompanied by an abnormality in the mitral valve and/or tricuspid valve. This defect produces at least some blood leakage (regurgitation) back though the valves. Primum ASDs rarely close on their own, and surgery is almost always necessary.
  
  
• Secundum ASDs are located more toward the middle of the septum. During fetal development, there is a normal hole in the atrial septum called the foramen ovale, which is covered by the septum primum. After birth, when pressure rises in the left atrium and the lungs start working, the septum primum should naturally seal the hole. Secundum ASDs occur when the septum primum is absent or somehow malformed.
  
  
• Sinus Venosus ASDs are located higher and usually involve the right upper pulmonary vein.

According to the National Institutes of Health (NIH), ASD occurs in four out of 100,000 people. It is about two to three times more common in girls than in boys. It may be present alone, or may exist with other defects, including:

• Ventricular septal defect (VSD). This defect refers to a hole in the septum between the lower chambers of the heart (ventricles). It is also considered a left–to–right shunt.
  
  
• Total anomalous pulmonary venous return (TAPVR). Instead of the pulmonary veins connecting with the left atrium, as they should, they connect to the right atrium.
  
  
• Mitral valve abnormalities. These valvular defects can affect the blood flow, often causing it to leak backward (regurgitation) instead of flowing forward.

Although a physician can often find an ASD by listening for a heart murmur (abnormal heart sound), the majority of ASD patients have no symptoms. Therefore, the defect may be found when a person is 3 or 4 years old, or when a person is 30 or 40 years old.

If symptoms do appear in childhood, they may include frequent chest colds and upper respiratory infections that may require hospitalization. If the defect is large enough, side effects may include malnutrition (despite a normal diet) coupled with stunted growth. This is because the heart is doing extra work, thus demanding more calories and slowing the metabolism. Finally, the more congested the lungs become, the more susceptible a person is to pulmonary hypertension, a condition in which blood pressure in the lung's blood vessels is high. Symptoms of pulmonary hypertension include:

The symptoms of ASD are similar to other less serious medical conditions or problems. If individuals, especially children, exhibit these symptoms, they should be evaluated by a physician.

Because children with an ASD often have no symptoms, the ASD may be first noticed during routine testing or medical check-ups. Most commonly, it is found when a physician uses a stethoscope to listen for a heart murmur. However, not all heart murmurs are signs of ASD. Therefore, the physician will often listen to the patient’s heart a number of times over a six- to 12-month period and may refer the patient to a cardiologist.

To help diagnose ASD, the cardiologist may first order an echocardiogram. This non-invasive test uses sound waves to track the structure and function of the heart. A moving image of the patient’s beating heart is played on a video monitor, where a physician can study the heart’s thickness, size and function. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage (regurgitation). During this test, a Doppler ultrasound may also be done to evaluate blood flow. The echocardiogram, however, is limited because it cannot detect abnormal blood vessel connections from the lungs. An MRI is often ordered for this purpose (see below).

Other tests that might be ordered include:

• Chest x-ray. A diagnostic test that uses radiation to produce images of internal organs, structures and tissues. A chest x-ray may indicate an enlarged heart due to the increased blood flow. The test also may detect changes that can occur in the lungs due to ASD.
  
  
• Angiogram. In this test, a long, thin catheter is threaded through an artery into the heart, where it is used to inject special contrast dye that is visible under x-ray. This can help the physician trace the flow of the blood through the heart. Because of advancing MRI and ultrasound technology, this test is rarely used today, although catheter-based interventions remain an important part of therapy for ASDs.
  
  
• Magnetic resonance imaging (MRI). In this test, powerful magnets are used to create images of the heart on a screen, which can help the physician visualize the function of the heart. Researchers are also testing a newer diagnostic tool called an XMR. This test combines the MRI with a traditional x-ray to allow better visualization of the heart.

Most physicians agree that no matter how small the hole, ASD should be treated during childhood if it is detected. Closing the hole in a child can prevent serious medical problems later in life. ASD is typically repaired in adults as well. Treatment of ASD depends on a number of factors, including the size of the hole, the severity of the symptoms and how the condition is affecting the heart muscle and function.

Treatment may include certain medications, such as diuretics, which flush out excess fluids and minerals from the body. Removing excess fluids can lower blood pressure and somewhat relieve the burden on the right ventricle. This treatment is usually reserved for larger ASDs. Additionally, digoxin, which reduces the exertion of the heart muscle, may be used with larger ASDs.

In some cases (e.g., primum ASDs),  open-heart surgery may be necessary to correct the defect. This is no longer the optimal treatment for less serious cases, but it remains an important option for patients with more severe forms of ASD. The surgery is usually done by age 5, before any significant damage or malformation develops as a result of the defect.

The strategy for closing a defect during surgery depends on the size of the hole. Smaller holes are closed by stitches (sutures). Larger defects are patched with a large “swatch” made of either a synthetic material or the patient’s own tissue (often from the fluid-filled sac around the heart called the pericardium).

When an ASD occurs with other defects, the surgery becomes more complicated. However, the surgery to treat an ASD alone has a relatively low risk and a high rate of success; the risk of death from surgery is less than 1 percent.

More recently, less serious cases (secundum ASDs) have been treated with a catheter closure technique. In one such procedure, a septal occluder (a type of elastic catheter made of flexible wire) is fed through an artery and guided to the heart. There, it is implanted in the septal hole. Once in place, it is expanded to lie across the defect and seal the hole. In another catheter-based procedure, a clamshell or umbrella device is opened inside the heart to block the hole.

By using a catheter instead of opening up the chest through surgery, patients face much less trauma and pain and do not undergo cardiopulmonary bypass, which carries risks of its own. They can leave the hospital sooner and scarring is greatly reduced.

Researchers are also evaluating a method to squeeze a patch into a catheter and snake it through the body up to the heart. Once in place, the physician can place the patch over the hole, sealing it. The patch eventually becomes covered with the body’s tissues. In these catheter procedures, physicians will often prescribe antibiotics to help prevent infection and complication.

Another treatment method is minimally invasive heart surgery in which three or four small incisions are made in the chest and specially designed instruments are passed into the chest to repair the ASD. For smaller ASDs, this has become the treatment of choice when surgery is indicated. During this procedure, a partial lower sternotomy is used, meaning the surgeon cuts through the lower part of the breastbone to expose the heart.

In the future, physicians may use robotic technology to further reduce the trauma and complications associated with ADS.

Once treated, ASDs are usually cured for life and there is no need for taking medication or other treatments. The repair of the defect generally has no harmful effects on normal growth and development. Patients, especially children, may need to be monitored by a cardiologist for a period of time. 

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients or parents may wish to ask their doctor the following questions about atrial septal defect (ASD):

1. Why do you suspect an ASD?
   
   
2. What tests will be used to diagnose this condition?
   
   
3. Does my child have any other congenital heart defects?
   
   
4. What type of ASD does my child have?
   
   
5. What are the treatment options for this condition?
   
   
6. What are the risks associated with these treatments?
   
   
7. What type of surgery will my child need and how soon will it be done?
   
   
8. What is the recovery period for this type of surgery?
   
   
9. How will it affect my child later in life?
   
   
10. Will my child need to take any medications?
    
    
11. How will the condition be monitored?
    
    
12. Is there a chance the hole can re-open?