What complication is most associated with untreated atrial septal defect in children?

Untreated atrial septal defects (ASD) can lead to a significant increase in blood flow to the lungs due to the left-to-right shunt that occurs when blood flows from the left atrium to the right atrium. Over time, this increased pulmonary blood flow can cause damage to the lung vasculature, leading to pulmonary hypertension.

Pulmonary hypertension in children with untreated ASD develops as a result of chronic volume overload of the pulmonary arteries, which can lead to vascular remodeling and increased vascular resistance. This condition can progress to serious complications, such as right heart failure and further cardiovascular issues.

While other complications like heart failure and arrhythmias can also be associated with ASD, pulmonary hypertension is the most direct and prevalent complication arising specifically from the effects of untreated shunting over time. It's essential to monitor and manage these defects to prevent the development of pulmonary hypertension, which can significantly impact the long-term health of affected children.