Eisenmenger syndrome is a rare progressive heart condition that develops in some individuals with structural malformations of the heart that are present from birth (congenital heart defects). The disorder is characterized by increased blood pressure in the main blood vessel (pulmonary artery) connecting the heart to the lungs (pulmonary hypertension) and improper blood flow within the heart.
The normal heart has four chambers. The two upper chambers, known as atria, are separated from each other by a fibrous partition known as the atrial septum. The two lower chambers are known as ventricles and are separated from each other by the ventricular septum. Valves connect the atria (left and right) to their respective ventricles. The valves allow for blood to be pumped through the chambers. Blood travels from the right ventricle through the pulmonary artery to the lungs where it receives oxygen. The blood returns to the heart through pulmonary veins and enters the left ventricle. The left ventricle sends the now oxygen-filled blood into the main artery of the body (aorta). The aorta sends the blood throughout the body.
The most common congenital heart defect associated with Eisenmenger syndrome is a ventricular septal defect (VSD) or a "hole in the heart" between the two lower chambers of the heart (left ventricle and right ventricle. This defect allows blood to flow from the left ventricle into the right ventricle (left-to-right shunt). The shunt causes increased blood flow into the lungs eventually resulting in pulmonary hypertension, which causes progressive damage to the small blood vessels in lungs (pulmonary vascular disease). As the damage continues, pulmonary hypertension increases and the small blood vessels become thickened or blocked hampering the flow of blood. Ultimately, blood flow is reversed back through the shunt so that blood flows from the right ventricle into the left ventricle (right-to-left shunt) bypassing the lungs completely. A variety of symptoms including life-threatening complications may occur.
Eisenmenger syndrome specifically refers to the combination of pulmonary hypertension and right-to-left shunting of the blood within the heart.