More About Ejection Fraction

Just because the heart is a pump, don’t think it’s like any other kind of pump you ever saw. At last month’s meeting, Joe Fay said he deals with the electrical system of the heart, not the plumbing. In most other pumps, the electrical system carries power to an electric motor, and the plumbing carries the fluid that’s being pumped. The heart is different.

The heart’s electrical system is a control system. It runs inside the heart from the sinus node, in the right atrium, to the other chambers. The ICD Joe told us about supports that system. Failure of that system can cause “sudden cardiac death.”

The plumbing Joe referred to is the coronary arteries, which run down from the aorta and around the heart. They supply fuel and oxygen to the chemical motor in the heart. Failure of that system can cause a heart attack - which can then cause failure of other systems.

The heart also has another plumbing system, which - as in most other pumps - carries the fluid being pumped - in this case, blood. It includes the heart’s four chambers and four valves. Failure of that system can cause “heart failure.”

One of the measurements used to describe heart failure is the ejection fraction. Each time the heart beats, the left ventricle (m in the diagram) fills to about half a cup from the left atrium k, and then squeezes out about half of it. (At the same time, the right ventricle a fills from the right atrium d and squeezes out about half.) If it squeezed out exactly half, the ejection fraction would be 50 percent.

The ejection fraction is whatever fraction of its contents the left ventricle squeezes out at each beat, expressed as a percentage. One way to determine the ejection fraction is from an echocardiogram, which shows an image of the beating heart.

Somebody asked whether the ejection fraction could be 100 percent. It can’t. The heart is a muscular bag. If you could squeeze it between your hands, you might be able to squeeze out 100 percent. But a bag squeezing itself remains round. It can’t squeeze its inside to zero, so it can’t empty itself.

Sometimes, as Joe mentioned, the two ventricles don’t contract at the same time. Look at the septum, the wall between the ventricles, marked o in the diagram. If the left ventricle contracts, and the right one doesn’t, the septum is pushed toward the right, and the left ventricle can’t squeeze out as much if the septum didn’t move.

One more comment: why does heart failure cause fluid to accumulate in the lungs? We think of the left ventricle as pumping blood to the body. But in doing so, it pumps blood from the lungs. If it can’t pump blood fast enough from the lungs, the lungs fill up, and you have CHF, congestive heart failure. Sometimes the lungs don’t fill up, so CHF now stands for chronic heart failure.