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. Without this septum, or if there is a defect in this septum, it is possible for blood to travel from the left side of the heart to the right side of the heart, or the other way around.
Since the right side of the heart contains venous blood with a low oxygen content, and the left side of the heart contains arterial blood with a high oxygen content, it is beneficial to prevent any communication between the two sides of the heart and prevent the blood from the two sides of the heart from mixing with each other.
During development of the fetus, the inter-atrial septum develops to eventually separate the left and right atria. The foramen ovale remains open during fetal developement to allow blood from the venous system to bypass the lungs and go to the systemic circuation. This is because prior to birth, the oxygenation of the blood is via the placenta and not the lungs. A layer of tissue begins to cover the foramen ovale during fetal development, and will close it completely soon after birth. After birth, the pressure in the pulmonary circulation drops, and the foramen ovale closes. In approximately 30% of adults the foramen ovale does not seal over. In this case, elevation of pressure in the pulmonary circulation (ie: pulmonary hypertension due to various causes, or transiently during a cough) can cause opening of the foramen ovale. This is known as a patent foramen ovale (PFO).
The septum is a wall that separates the heart's left and right sides. Septal defects are sometimes called a "hole" in the heart. A defect between the heart's two upper chambers (the atria) is called an atrial septal defect (ASD). When there is a large defect between the atria, a large amount of oxygen-rich (red) blood leaks from the heart's left side back to the right side. Then this blood is pumped back to the lungs, despite already having been refreshed with oxygen. This is inefficient, because already-oxygenated blood displaces blood that needs oxygen. Many people with this defect have few, if any, symptoms.
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.