Glossary of Terms

Atrial Septal Defect (ASD)
Atrial septal defect is the second most common congenital defect. It is an abnormal opening between the atria. It causes changes in blood flow similar to those in ventricular septal defect except for the volume of blood shunted. Because of lower pressure in the atria, ASD shunts less blood from the left to the right side. Consequently, ASD rarely causes congestive heart failure in young children. However, the decreased systemic cardiac output from the ASD fails to deliver optimal oxygen and nutrients to the tissues. This results in impaired growth so children with ASD tend to be small for their age. Also, pulmonary overload (interstitial edema), predisposes the child to frequent respiratory infections.

Left-to-right shunts initially markedly increase pulmonary blood flow. Overcirculation of this vasculature may gradually make the vessels fibrotic and less elastic. This change produces hypertension within the pulmonary circuit and eventually reverses the intracardiac shunt from the right to left.

ASD is usually corrected in late childhood to prevent permanent pulmonary vascular changes associated with pulmonary overload. More info...