What is Atrial Septal Defect (ASD)?
Normal anatomy of the heart: The normal heart consists of 4 chambers - the right & left atrium (These are the chambers that receive the blood - the right atrium receives impure blood from the rest of the body and left atrium receives pure blood from the lungs.) and the right & left ventricles (These are the chambers that pump the blood from the heart – right ventricle receives blood from right atrium and pumps the impure blood to the lungs via the pulmonary artery and left ventricle receives pure blood from the left atrium and pumps the pure blood to the rest of the body via another artery called as the aorta). The impure blood in the right atrium is separated from pure blood in the left atrium by the atrial septum. A hole in this septum leads to blood flow from left atrium to the right atrium. This is because the pressure of blood in left atrium is higher than that of the right atrium.

What happens in an ASD?
As the right atrium receives blood from 2 places- impure blood from rest of the body and pure blood from left atrium, more blood reaches the right ventricle. The ventricle now has to pump harder to send this increased amount of blood into the lungs. As a result extra blood flows into the lungs than it normally does. This extra blood flow in the lungs can cause frequent chest infections. On chronic high blood flow, the blood vessels in the lungs become hard and thick leading to high pressure in the pulmonary vessels. This condition is called pulmonary hypertension. Subsequently the heart may also fail as the right ventricle may become weak due to constant hard work. These changes take many years to develop.
Another problem with ASD is arrhythmia (irregular rhythm of the heart). This occurs as the right atrium enlarges in size due to increased blood volume. That causes a disturbance in the heart's electrical activity causing it to beat faster leading to a condition called as Atrial Fibrillation. All these changes are seen with large ASD.
Many children with small ASD are not even symptomatic till they are in their 30’s or 40’s.
Sometimes clots may enter the right atrium and pass through the ASD into left atrium which then passes into the aorta and to the brain leading to a stroke – phenomenon known as paradoxical embolization. (Blood flow in the veins is sluggish and some clots may form. In a normal person, the clots pass from the right atrium to the lungs where they are filtered and prevented from entering into the pure blood). It is because of this risk, that even a small ASD needs to be closed.

How is ASD diagnosed?
ASD is suspected on clinical examination by fixed splitting of the second heart sound and confirmed by echocardiography (ultrasound of the heart).

Should an ASD be closed?
Yes. Most ASD require to be closed. Sometimes a small ASD such as a stretched PFO may be left untouched.

Last created on 6-05-2003
Last updated on 18-11-2006