Eisenmenger syndrome is usually caused by an unrepaired hole (shunt) between the main blood vessels or chambers of the heart. A shunt is a heart problem present at birth (congenital heart defect).
To understand how Eisenmenger syndrome affects the heart and lungs, it's helpful to know how the heart typically works.
How the heart works
The heart is divided into chambers — two upper chambers (atria) and two lower chambers (ventricles).
- The right side of the heart moves blood to the lungs through blood vessels (pulmonary arteries).
- In the lungs, blood picks up oxygen and then returns to the left side of the heart through the pulmonary veins.
- The left side of the heart then pumps the blood through the aorta and out to the rest of the body.
Heart valves control the flow of blood into and out of the chambers of the heart. These valves open to allow blood to move to the next chamber or to one of the arteries, and then close to keep blood from flowing backward.
How Eisenmenger syndrome develops
Heart problems present at birth (congenital heart defects) that can cause Eisenmenger syndrome include:
- Ventricular septal defect. This is the most common cause of Eisenmenger syndrome. There is a hole (shunt) in the wall of tissue that divides the right and left sides of the heart's main pumping chambers (ventricles).
- Atrioventricular canal defect. This is a large hole in the center of the heart where the walls between the upper chambers (atria) and lower chambers (ventricles) meet. Some of the valves in the heart also may not work properly.
- Atrial septal defect. This is a hole in the wall of tissue that divides the right and left sides of the upper chambers of the heart (atria).
- Patent ductus arteriosus. This is an opening between the pulmonary artery that carries oxygen-poor blood to the lungs and the artery that carries oxygen-rich blood to the rest of the body (aorta).
In any of these heart problems, blood flows in a way it usually doesn't. As a result, pressure rises in the pulmonary artery. Over time, the increased pressure damages the smaller blood vessels in the lungs. The damaged blood vessel walls make it difficult to pump blood to the lungs.
In Eisenmenger syndrome, there's increased blood pressure in the side of the heart that has oxygen-poor blood (blue blood). The blue blood goes through the hole (shunt) in the heart or blood vessels. Oxygen-rich and oxygen-poor blood now mix. This causes low blood oxygen levels.