A number worth watching

Content provided by the Faculty of the Harvard Medical School

A number worth watching

The heart’s ejection fraction can be a helpful number to know.

A few ounces at a time, your heart moves about 2,000 gallons of blood a day. On the surface, the pumping process seems simple. The heart’s upper chambers, the atria, relax and fill with blood. They squeeze, sending their contents to the ventricles below. Once full, the ventricles contract, pushing blood to all parts of the body.

There’s more to it, of course, involving electrical pathways, valves, and a host of other elements. One of the intricacies is how much blood the heart sends into circulation with each beat. No matter how forceful, contractions don’t squeeze out every last drop of blood from a chamber; some is left behind. The ratio of the amount of blood ejected, or pumped, with each beat to the amount the chamber holds when it is relaxed is called the ejection fraction. It can be a helpful guide for some people with heart disease.

The simplest way to measure ejection fraction is with an echocardiogram. This painless test uses sound waves to make a movie of the heart as it beats. The ejection fraction is then determined by comparing the images of a chamber as it fills to capacity with images after it contracts.

This is usually done for the left ventricle, the chamber that sends oxygenated blood to most of the body. Sometimes an ejection fraction is calculated for the right ventricle, which pumps blood to the lungs for oxygenation.

The ejection fraction can also be determined during a nuclear exercise stress test or a multiple gated acquisition scan. Both of these tests use tiny amounts of radioactive tracers.

The mechanics of ejection As the heart relaxes between beats (diastole), the ventricles fill with blood. When it contracts (systole), it pushes out most — but not all — of the blood that filled the ventricles.

What ejection fraction means

A normal ejection fraction is between 55% and 75%, meaning the left ventricle squirts out 55%–75% of the blood it holds when full.

A low ejection fraction is usually caused by some “insult” to the heart, like a heart attack, chronic high blood pressure, the aftermath of a cardiac infection, or an inherited condition that causes the left ventricle to enlarge. A major heart attack, for example, can drop the ejection fraction as low as 10%.

In some people, an ejection fraction below 40% shows up as shortness of breath, excessive fatigue, swollen ankles and legs, and other signs of heart failure. In general, the lower the ejection fraction, the greater the limitations. Yet plenty of people with low ejection fractions aren’t hindered at all. At the same time, people with diastolic heart failure — a problem with the left ventricle’s ability to relax and fill with blood — can have severe limitations even when they have perfectly normal ejection fractions.

Ejection fraction, like blood pressure, can bounce up and down over the course of a day, as well as from day to day and week to week. It is influenced by medications, the amount of fluid in the bloodstream, the machine used to measure it, and even the clinician performing the test. A drop from 32% to 28% doesn’t mean anything. But going from 55% to 40% should make your doctor take notice.

Using the ejection fraction

Who needs to know their ejection fraction? It’s a helpful number for anyone with heart failure and a useful one for almost everyone with heart disease. It serves as a general gauge of heart function, not as a specific measure of how you are feeling or doing.

For most people with low ejection fractions, pumping problems in the left ventricle aren’t the only source of limitations. Equally important are out-of-condition muscles in the arms, legs, and elsewhere. If you have a low ejection fraction, exercising your body will do far more than resting your heart to make you feel better and improve your long-term health.

Exercise, in fact, is one of the few ways to boost a low ejection fraction. Medications that can stabilize or increase ejection fraction include beta blockers and ACE inhibitors.

The main thing to keep in mind about ejection fraction is that it isn’t a diagnosis. It’s a guide, another piece of the cardiovascular health puzzle, along with blood pressure, cholesterol level, resting heart rate, and other measures. A single ejection fraction isn’t nearly as important as its long-term trend and how you feel.

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Last updated:	August 21, 2006