If a large patent ductus arteriosus (PDA) is not corrected, what condition may develop?

A large patent ductus arteriosus (PDA) can lead to Eisenmenger Syndrome if it is left uncorrected over time. A PDA is a congenital heart defect characterized by the persistence of the ductus arteriosus, a blood vessel that connects the pulmonary artery to the aorta, which should close shortly after birth.

When a PDA remains open, it allows blood to flow from the aorta into the pulmonary artery, leading to increased blood flow to the lungs. Over years, this increased pulmonary blood flow can cause structural changes in the pulmonary vasculature, resulting in pulmonary hypertension. As the pressure in the pulmonary arteries increases, the right ventricle faces higher resistance, leading to right heart strain. Eventually, the pressure in the right side of the heart may exceed that of the left side, causing a reversal of blood flow (right-to-left shunt) through the PDA. This reversal can result in cyanosis and systemic desaturation, a hallmark of Eisenmenger Syndrome.

The development of Eisenmenger Syndrome is a serious consequence of untreated large PDAs, highlighting the importance of early diagnosis and intervention.