Developmental Pathophysiology, Develop. Physiol., Dr. D. Penney

Figure 4.04 - Atrial septal defect at the fossa ovalis:

A. This is the most common type. The left to right shunt is dependent on the fact that the RV offers less resistance to filling than does the LV.
B. A right to left shunt in ASD depends indirectly on elevated pulm. vasc. resistance. When this is present, the pulm. art. pressure rises and the RV hypertrophies. The stage may be reached when resistance to filling of the RV is greater than resistance to filling the LV - a right to left shunt across the ASD then occurs.

Abbreviations: IVC = inferior vena cava, LA = left atrium, LV = left ventricle, LPA = left pulmonary artery, LPV = left pulmonary vein, PA = pulmonary artery, RPA = right pulmonary artery, RPV = right pulmonary vein, SVC = superior vena cava

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