During prenatal development, shunts between the left and right atria and ventricles allow for efficient gas exchange between the placenta and fetus. These shunts, the foramen ovale and ductus arteriosus, normally close at birth, allowing the lungs to become the primary center for gas exchange. Atrial septal defects occur when the shunt between the atria does not close and blood is allowed to flow from the left to right atrium, whereas ventricular septal defects occur when the interventricular septum does not close and blood is allowed to flow from the left to right ventricle. A patent ductus ar-teriosus occurs when the embryological connection between the aorta and the pulmonary trunk persists after birth. Treatment is varied due to the wide
Table 21-1. Selected congenital heart disease types
Acyanotic (left-to-right shunt) heart lesions
Atrial septal defects Patent ductus arteriosus Ventricular septal defects
Cyanotic (right-to-left shunt) heart lesions
Double outlet right ventricle Ebstein's anomaly Pulmonary atresia Persistent truncus arteriosus Single-ventricle physiology Tetralogy of Fallot
Total anomalous pulmonary venous return Transposition of the great arteries Tricuspid atresia Obstructive heart defects Aortic valve stenosis Coarctation of the aorta Mitral valve stenosis Pulmonary valve stenosis range of severity present, with some acyanotic lesions closing spontaneously without intervention and others requiring medical and/or surgical intervention. With correction, children with these lesions can generally function normally and without significant physical limitations. Together, these defects represent 37%-46% of all congenital heart defects (Bernstein 2000).
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