Atrial septal defect (ASD) is characterized by a left-to-right shunt primarily due to the pressure differences between the left and right atria. In a typical heart, the left atrial pressure is higher than the right atrial pressure, especially during systole. When there is a defect in the atrial septum, which is the wall separating the left and right atria, blood can flow from the left atrium (where the pressure is higher) into the right atrium.
This shunting results in increased blood flow to the right side of the heart and subsequently to the pulmonary circulation. Over time, this can lead to volume overload in the right atrium and ventricle, increased pulmonary blood flow, and potential complications such as pulmonary hypertension or heart failure if left untreated.
In contrast, other conditions listed, such as pulmonary stenosis and coarctation of the aorta, do not exhibit a left-to-right shunt; instead, they create obstructions in blood flow that can lead to different physiological effects. Ventricular septal defect (VSD) also presents a left-to-right shunt, but in this specific context, the correct association relates directly to the atrial septal defect. Both