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An atrial septal defect (ASD) is an abnormal opening in the muscular wall separating the left and right upper chambers (atria) of the heart.
During normal development of the fetal heart, there is an opening in the wall (septum) separating the left and right upper chambers of the heart. Normally, the opening closes before birth, but if it does not, the child is born with a hole between the left and right atria. This abnormal opening is called an atrial septal defect and causes blood from the left atrium to flow (or "shunt") across the hole into the right atrium.
Different types of atrial septal defects occur, and they are classified according to where in the separating wall they are found. The most commonly found atrial septal defect, called secundum atrial septal defect, occurs
Abnormal openings also form in the upper part of the atrial septum (called sinus venosus ASD) where the superior vena cava and right atrium join, and lower parts of the atrial septum (called primum ASD). A sinus venosus ASD usually involves the right upper pulmonary vein, while a primum ASD often occurs along with an abnormality in the mitral valve and/or tricuspid valve, and causes some blood leakage (regurgitation) back through the valves.
Atrial septal defects can occur alone or in combination with other congenital heart disorders, such as ventricular septal defect. They can be as small as a pinpoint or as large as the space where the entire septum should be located.
Atrial and ventricular septal defects are the most common congenital heart defects. Atrial septal defect accounts for 4–10 percent of all cases of congenital heart disease in the United States. Abnormal openings in the atrial septum are twice as common in females as in males.
Author Info: Dominic De Bellis Ph.D., Angela M. Costello, Thomson Gale, Gale, Detroit, Gale Encyclopedia of Children's Health, 2006This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.
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