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All about atrial septal defect (ASD) causes of atrial septal defect types of atrial septal defects symptoms of atrial septal defect diagnosis of atrial septal defect atrial septal defect treatments

What causes atrial septal defects?

The heart is forming during the first 8 weeks of fetal development. It begins as a hollow tube, then partitions within the tube develop that eventually become the septa (or walls) dividing the right side of the heart from the left. Atrial septal defects occur when the partitioning process does not occur completely, leaving an opening in the atrial septum.

Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality, or environmental exposure, causing heart problems to occur more often in certain families. Most atrial septal defects occur sporadically (by chance), with no clear reason for their development.

In normal individuals, the chambers of the left side of the heart make up a higher pressure system than the chambers of the right side of the heart. This is because the left ventricle has to produce enough pressure to eject blood to the entire body, while the right ventricle has to produce enough pressure to eject blood to only the lungs. In the event of an atrial septal defect, blood will flow from the left atrium to the right atrium. This is called a left-to-right shunt. This extra blood will cause a volume overload of both the right atrium and the right ventricle.

Any process that increases the pressure in the left ventricle can cause worsening of the left-to-right shunt. This includes hypertension, which increases the pressure that the left ventricle has to generate in order to open the aortic valve during ventricular systole, and coronary artery disease which increases the stiffness of the left ventricle, thereby increasing the filling pressure of the left ventricle during ventricular diastole.

The right ventricle will have to push out more blood than the left ventricle due to the left-to-right shunt. This constant overload of the right side of the heart will cause a overload of the entire pulmonary vasculature. Eventually the pulmonary vasculature will develop pulmonary hypertension to try to divert the extra blood volume away from the lungs. The pulmonary hypertension will cause the right ventricle to face increased afterload in addition to the increased preload that the shunted blood from the left atrium to the right atrium caused. The right ventricle will be forced to generate higher pressures to try to overcome the pulmonary hypertension. This may lead to right ventricular failure (dilatation and decreased systolic function of the right ventricle) or elevations of the right sided pressures to levels greater than the left sided pressures.

When the pressure in the right atrium rises to the level in the left atrium, there will no longer be a pressure gradient between these heart chambers, and the left-to-right shunt will diminish or cease. If left uncorrected, the pressure in the right side of the heart will be greater than the left side of the heart. This will cause the pressure in the right atrium to be higher than the pressure in the left atrium. This will reverse the pressure gradient across the ASD, and the shunt will reverse; a right-to-left shunt will exist. This phenomenon is known as Eisenmenger's syndrome. Once right-to-left shunting occurs, a portion of the oxygen-poor blood will get shunted to the left side of the heart and ejected to the peripheral vascular system. This will cause signs of cyanosis.

More information on atrial septal defect

What is an atrial septal defect? - An atrial septal defect (ASD) is a group of congenital heart diseases that involve the inter-atrial septum of the heart. The inter-atrial septum is the tissue that separates the right and left atria from each other.
What causes atrial septal defect (ASD)?
- Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality, or environmental exposure, causing heart problems to occur more often in certain families.
What are types of atrial septal defects? - There are many types of atrial septal defects. They are differentiated from each other by whether they involve other structures of the heart and how they are formed during the developmental process during early fetal development.
What are the symptoms of an atrial septal defect? - Many children have no symptoms and seem healthy. However, if the ASD is large, permitting a large amount of blood to pass through to the right side of the heart, the right atrium, right ventricle, and lungs will become overworked, and symptoms may be noted.
How is an atrial septal defect diagnosed? - Most individuals with a significant ASD are diagnosed in utero or in early childhood with the use of ultrasonography or auscultation of the heart sounds during physical examination.
What are treatment options for atrial septal defect? - An atrial septal defect is most commonly closed by open-heart surgery. The surgeon may be able to directly close the hole with sutures or, depending on the size and shape of the hole, may need to close it with a patch.
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