What does Eisenmenger syndrome result from?

Eisenmenger syndrome arises from a long-standing left-to-right shunt, such as that seen in conditions like atrial septal defect or ventricular septal defect. Over time, this shunting leads to increased blood flow to the pulmonary circulation, resulting in pulmonary hypertension. As pulmonary vascular resistance increases, the pressure in the right ventricle may eventually exceed that of the left ventricle, causing the shunt to reverse from right to left. This reversal results in cyanosis and other systemic effects due to deoxygenated blood being circulated to the body.

The key factor in Eisenmenger syndrome is the transition from a left-to-right shunt to a right-to-left shunt due to the development of pulmonary hypertension. This condition emphasizes the importance of early intervention in patients with congenital heart defects to prevent the progression to Eisenmenger syndrome.