Atrial Septum, Atrial Septal Defect and Anomalous Pulmonary Venous Drainage

Abstract

Isolated atrial septal defect is seldom diagnosed in the early months of life. The compliance of the right ventricle slowly increases above that of the left ventricle. Consequently, the L-R atrial shunt gradually develops. Furthermore, the L-R shunt in atrial septal defect rarely causes clinical symptoms. The patient is commonly referred to the pediatric cardiologist for analysis of a cardiac murmur. An ejection murmur over the pulmonary area with typical fixed splitting of the second sound with a loud pulmonary component is usually the first sign of an atrial septal defect with a significant L-R shunt. In these cases the chest X-ray reveals increased pulmonary vascular markings and cardiomegaly. The cardiomegaly is mainly due to the dilated right ventricle which is readily observed by echocardiography. The absence of evidence of pulmonary hypertension on the pulmonary valve M-mode echocardiogram and the possible presence of paradoxical septal motion indicate that volume overload is the only cause of the right ventricular dilatation. Two-dimensional echocardiography reveals normal attachment of the tricuspid valve without a significant prolapse. The atrial septal defect is best visualized directly in the subcostal four chamber view because in this cross-section the ultrasound beam has a more perpendicular relation with the atrial septum compared with other views. The apical four chamber view (2) and the parasternal short axis view, at the level of the great arteries (3), may also be used but ultrasound coming from these windows tends to pass parallel to the atrial septum. Therefore, central septal ‘dropouts’ easily occur, particularly when the overall resolution is inadequate or the gainsettings are not properly adjusted.