Seeing the heart with sound (echocardiogram)
Silent sound waves don't seem like they'd be much use. They are, though. They're the force behind submarine trackers and fish finders. In medicine, they give expectant parents a first look at their developing baby, and let doctors peer into the heart. An echocardiogram, which uses these sound waves, creates images with more detail than an x-ray but without any radiation exposure. It can also create real-time videos that show the heart in action.
Why is it done?
An echocardiogram can reveal the size and shape of the heart, the thickness and motion of its muscular wall, and the operation of its valves. It can show blood flow patterns through the heart and determine how much blood remains in the heart after each contraction. Because of this versatility, doctors perform echocardiograms to
- look for the cause of chest pain, shortness of breath, irregular heart beats, or murmurs or other abnormal heart sounds
- evaluate the heart's valves
- check the pumping function of the heart
- measure the size and shape of the heart's chambers
- look for a blood clot or tumor in the heart
- check for the accumulation of fluid around the heart (pericarditis)
- look for congenital heart defects.
Practice guidelines from the American Heart Association call echocardiography the "single most useful diagnostic test in the evaluation of patients with heart failure." One of the things it can do is determine the heart's ejection fraction, a ratio of how much blood remains in the left ventricle after a contraction to how much it can hold. People with heart failure often have a low ejection fraction.
What's the procedure?
Having a standard echocardiogram (also called cardiac echo or cardiac ultrasound) is simple, painless, and relatively quick. No special preparation is needed. You lie on a bed or table with all or part of your chest exposed. Small metal disks attached to your arms and legs record your heartbeats. A doctor, nurse, or sonographer slides an instrument called a transducer across your chest. The transducer, which looks like a microphone, emits sound waves a thousand times smaller than the highest pitch humans can hear and captures them as they bounce back off various heart tissues. A computer transforms the sound waves into moving pictures that are displayed on a monitor.
During the test, you might be asked to hold very still, breathe in and out slowly, hold your breath, or lie on your left side.
The standard transthoracic (meaning across the chest) echocardiogram can't always yield clear videos or provide the information needed to make a diagnosis. Several modifications can help.
Doppler ultrasound. This echocardiogram add-on shows blood moving through the heart. The different speeds and directions of blood flow are represented by different colors and sometimes sounds. Abnormal speed across a heart valve may indicate a leaky valve or show the extent of a leak.
Stress echocardiogram. One way to see how the heart behaves when stressed is to perform a two-stage echocardiogram: once while relaxed and again immediately after walking or running on a treadmill. Exercise-caused changes in the motion of a section of heart muscle can indicate poor blood flow to that part of the heart, possibly due to one or more narrowed or blocked coronary arteries. Sometimes the heart is stressed with medications instead of exercise.
Transesophageal echocardiogram. A barrel chest, excess body fat, some lung diseases, and other physical conditions can absorb sound waves as they leave the transducer or bounce back from the heart. One way to get around this interference involves maneuvering a tiny transducer down the throat and into the lower part of the esophagus.
July 2008 update