Begin with a heart defect... I was born with a heart murmur. The doctors told my mother that it would probably never bother me. They were wrong.
Each time my heart beat, my heart defect allowed blood to go from the left side of my heart to the right side.
The left ventricle is very strong. It pushes blood out to the farthest part of my body... all the way down to my toes.
The right ventricle is not so strong. It only needs to push blood as far as my lungs.
With every beat of my heart the extra blood from the left side made the right side work harder. Over time the right side became stronger to deal with the extra load, and the extra strength of it raised the blood pressure in my lungs.
Lungs are supposed to be a low pressure system, with red blood cells moving gently through beds of tiny fragile capillaries, exchanging the carbon dioxide they carried from my body for oxygen I breathed in.
The blood pressure in my lungs got high enough to cause some of the capillary beds to die and be replaced with scar tissue. This reduced the blood volume in my lungs, and if you remember any high school physics, when you reduce the volume of a closed system, you raise the pressure. The higher pressure makes the damage happen faster. This high pressure in my lungs is called Pulmonary Hypertension.
The scar tissue does not contribute to the oxygen exchange that is supposed to be taking place in my lungs. So, my body figured I needed more red blood cells to carry the oxygen I need. Making more red cells is an adaptation that allows people to live in places like the tops of really high mountains. It is called the High Altitude Adaptaion. My body must have thought I moved to a city a mile higher than Denver!
Too many red blood cells is called Polycythemia. Too many red blood cells makes my blood thicker, and I have to be sure to drink lots of water to keep my blood from getting sludgy. My mom is always worrying about me getting dehydrated! Have some more water, she says. I wish she would say Have some more soda!
Another problem with too many red blood cells - they get to be so many that they outnumber the platelets by a lot. Then I am at risk for uncontrolled bleeding, and at the same time, I am at risk for random clotting. My doctors are more worried about clots, so I take a medicine to make my blood make clots more slowly. The medicine is called Coumadin or Warfarin, and has very interesting origins.
Sometimes when I am exerting myself, I feel very faint. This happens because the pressure in the right side of my heart gets high enough for the blood to go the other way through my heart defect, and blood that has just come from my body gets pushed into the left side of my heart, and then sent back out to my body, without going through the lungs to pick up fresh oxygen. The doctors called this Reversal of the Shunt.
All these things together - the underlying heart defect, the pulmonary hypertension, the polycythemia and the reversal of the shunt - are what makes Eisenmenger's Syndrome.
This definition was written by Margret's Mom, at Margret's request, so it would read as if Margret was doing the explaining.
If you are a doctor, a teacher or a medical student and need a clear explanation of Eisenmenger's Syndrome, I give you permission to use this one. Please give author's credit to Margret and her Mom.