What is the direction of the shunt in an atrial septal defect?

What is the direction of the shunt in an atrial septal defect?

• A. Right-to-left shunt
• B. No shunt
• C. Left-to-right shunt
• D. Bidirectional shunt only with exercise

Answer: (C)

The main concept is that the direction of a shunt depends on the pressure difference between the two chambers. In an atrial septal defect, the left atrial pressure is higher than the right atrial pressure, so blood flows from left to right through the defect into the right atrium. This creates a left-to-right shunt and increased blood flow to the lungs. Over time, if the pulmonary circulation becomes scarred and the pulmonary vascular resistance rises, the pressure gradient can reverse, leading to a right-to-left shunt (or bidirectional shunting in some cases), as seen in Eisenmenger syndrome. But initially, the typical direction is left-to-right.

The main concept is that the direction of a shunt depends on the pressure difference between the two chambers. In an atrial septal defect, the left atrial pressure is higher than the right atrial pressure, so blood flows from left to right through the defect into the right atrium. This creates a left-to-right shunt and increased blood flow to the lungs.

Over time, if the pulmonary circulation becomes scarred and the pulmonary vascular resistance rises, the pressure gradient can reverse, leading to a right-to-left shunt (or bidirectional shunting in some cases), as seen in Eisenmenger syndrome. But initially, the typical direction is left-to-right.