What is the main complication of Eisenmenger's syndrome?

Eisenmenger's syndrome is characterized by a reversal of a left-to-right shunt into a right-to-left shunt due to the development of pulmonary hypertension in patients with certain congenital heart defects. The key complication in this syndrome arises from the increased pressure in the pulmonary circulation, leading to significant vascular changes and ultimately progressive pulmonary hypertension.

As pulmonary artery pressure increases, the right ventricle faces a heavier workload, and over time, this can cause right ventricular hypertrophy and later right heart failure. However, the defining characteristic of Eisenmenger's syndrome is the long-term consequence of this pulmonary hypertension leading to the reversal of blood flow, which is a critical point in understanding the overall pathophysiology.

Increased pressure in the pulmonary vessels may also cause damage to the vascular endothelium, leading to further complications, including arrhythmias, strokes, and heart failure. While all these conditions can develop in patients with Eisenmenger's syndrome, pulmonary hypertension is the primary and most characteristic complication, as it directly induces the changes that define the syndrome.

Thus, the main complication of Eisenmenger's syndrome is indeed pulmonary hypertension, representing the underlying mechanism that drives the clinical manifestations of this condition.