Atrial Septal Defects
 

• What is an Atrial Septal Defect?
   
• Changes in the heart caused by an ASD
   
• Treatment
   
• General Considerations
   
• References
   

Atrial Septal Defects (ASD) are among the most common types of congenital heart defects. In general the defect is simply a hole in the wall (septum) between the top two chambers of the heart (Atria). There are three types of ASD's named in relation to their position in the atrial septum. Your doctor will identify the type of ASD you have and if there are any associated defects present.

Ostium Secundum Atrial Septal Defect

Ostium secundum ASD is the most common type of ASD. It occurs in the center of the septum between the right and left atrium. A variant of this type of ASD is called a patent foramen ovale (PFO) and is very small.

Normal heart for comparison

Ostium Primum Atrial Septal Defect

Ostium primum is the next most common type and is located in the lower portion of the atrial septum. This type of ASD often will have a mitral valve defect associated with it called a mitral valve cleft. A mitral valve cleft is a slit-like or elongated hole in one of the leaflets ( anterior leaflet) that form the mitral valve.

Normal heart for comparison

Sinus Venosus Atrial Septal Defect

A sinus venosus defect is the least common type of ASD and is located in the upper portion of the atrial septum. A sinus venosus ASD often has an abnormal pulmonary vein connection associated with it. Four pulmonary veins, two from the right lung and two from the left lung, normally return red blood to the left atrium. Usually with a sinus venosus ASD, a pulmonary vein from the right lung will be abnormally connected to the right atrium instead of the left atrium. This is called an anomalous pulmonary vein.

Normal heart for comparison

All types of ASD's can occur as a single defect or in a combination with other types of heart defects. Many people will grow well into adulthood before an ASD causes symptoms or is diagnosed.

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The right and left sides of the heart are normally completely separate. When a hole (ASD) is present there is a connection between the right and left side of the heart allowing blood to pass through it from the higher pressure side (the left) to the right. This means that oxygen rich red blood will be "shunted" through the ASD from the left atrium (higher pressure zone) to the right atrium (lower pressure zone). The consequences of this are:

1. Right atrial and ventricular enlargement
   The increased blood volume to the right side of the heart caused by the left to right shunting of blood through the ASD will cause the right heart chambers to enlarge over time.

    

2. Tricuspid regurgitation
   As the right side chambers enlarge the valve between the right atrium and ventricle (tricuspid valve) becomes stretched apart and may not close properly. This allows some blood to leak backward (regurgitation) into the right atrium instead of flowing forward.

    

3. Pulmonary hypertension
   Over time the increased volume of blood flow to the right side of the heart can transmit increased pressure to the lungs and this is called pulmonary hypertension. Increased pressure in the lungs, over time, can cause irreversible changes in the pulmonary blood vessels. An irreversible change in the pulmonary blood vessels is called pulmonary vascular disease and can be a very serious complication of an ASD. (see Eisenmenger's syndrome)

    

4. Rhythm disturbances
   Each heart beat begins within a type of "pacemaker" which is a grouping of special cells in the right atrium. This "pacemaker" is called the sinus node. The sinus node generates an electrical impulse that travels around the heart and causes a heart beat When the right atrium becomes enlarged this will "irritate" the sinus node and disrupt the regularity of the heart beat resulting in atrial arrhythmias. A specific type of atrial arrhythmia called atrial fibrillation is often associated with an ASD.

    

5. Stroke
   Blood normally flows from the right sided chambers to the lungs and then to the left sided chambers and out to the body. If a blood clot or air bubble would enter the circulation it would normally be filtered out of the blood by the lungs. With an ASD, however, there is a small chance it could bypass the lungs and travel directly to the brain causing a stroke. Additionally if an irregular heart rhythm develops the risk of a blood clot forming in the right atrium is increased and therefore the risk for stroke is also increased.

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Treatment of an ASD depends on the size, location, degree of symptoms present and the effect the defect is having on the heart muscle. Surgical closure of the defect is the current standard. If the ASD is very small a more conservative approach may be taken depending on the situation . There have been investigations into non surgical methods of closure using catheter based placement of a device (like an umbrella") to occlude the defect. With continued advancement in equipment and technique this may become a more widely used option in the future. If an ASD is associated with high pulmonary pressures it may not be appropriate to close the defect and medical management of symptoms would be pursued. It is very important that early detection and regular evaluation be done to avoid this serious complication of an ASD.

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1. Establishing regular follow up with an adult congenital cardiologist.
    
2. Endocarditis precautions.
    
3. Timing for and type of repair if indicated.
    
4. Optimizing general cardiovascular and pulmonary health, e.g. proper exercise, weight control and smoking cessation.
    
5. Pregnancy counseling.
    
6. Close monitoring and control of blood pressure, pulse rate and rhythm.
    
7. Anticoagulation when indicated.
    

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1. Warnes CA, Fuster V, Driscoll DJ, McGoon DC: Atrial septal defect. In: Mayo Clinic Practice of Cardiology, 3rd edition, E. R. Giuliani, B. J. Gersh, M.D. McGoon, D. L. Hayes, H. V. Schaff (eds.), Mosby, St. Louis, 1996.

    

2. Pascoe RD, Oh JK, Warnes CA, Danielson GK, Tajik AJ, Seward JB: Diagnosis of sinus venosus atrial septal defect by transesophageal echocardiography. Circulation 94 (5):1049-1055, 1995.

    

3. Bergin ML, Warnes CA, Tajik AJ, Danielson GK: Partial atrioventricular canal defect: Long-term follow-up after initial repair in patients > 40 years old. J Am Coll Cardiol 25:1189-1194, 1995.

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