Stress Echocardiography
Background: Heart disease is the leading killer of Americans today, and heart attack is the most
visible sign of heart disease. A heart attack occurs when the blood supply to the heart is restricted
to the point that a portion of the heart muscle dies. This is usually brought on by blockages in the
arteries feeding the heart, known as coronary artherosclerosis, and try to determine the patient's
risk of developing a heart attack in the future. In addition these tests can be used to assess the
damage to the heart after a heart attack. One of these tests is the stress echocardiogram, in which
a patent's heart is "stressed" either with exercise or a chemical agent, and ultrasound images of
the heart are obtained.
Who can be tested? The stress echocardiogram is a very versatile procedure. It is equally diagnostic
in women or men of all ages. Diagnostically sufficient echocardiograms can be obtained in the vast
majority of patients. For the few that cannot be ideally imaged, other tests (such as nuclear
cardiac studies) are available. Usually, if the patient can walk adequately, he or she is asked to
walk on a treadmill to stress the heart. If they are unable to walk due to arthritis, lung disease
or other medical problems, their hearts can be stressed using an intravenous chemical agent known
as dobutamine. This chemical is similar to adrenaline, and works by increasing the heart rate and
force of heart contraction.
What does the test show? The echocardiogram is a remarkable tool that can obtain a wealth of
information about the heart. It can tell the size and strength of the heart muscle, the condition of
the heart valves, or if there is fluid around the heart. It can tell us if the patient has had a
previous heart attack and the extent of the damage. It can demonstrate blood clots or infections in
the heart. In case of the stress cardiogram, it can also tell if the blood supply to a portion of
the heart. is critically limited and how much of the heart is affected. In addition, it can tell us
if the heart muscle is simply "stunned" by its limited blood supply and might therefore improve in
strength if the blood supply is improved.
How is the test done? An echocardiogram (sound wave picture of the heart) is done on the patient while
he or she is at rest and displayed in a video screen for interpretation. The images are also stored
on video tape in digital format for later analysis and to create a permanent record of the exam.
Single representative heart beats imaged from four different angles are selected and stored in computer
memory. The patient is then stressed either by exercise or dobutamine until their heart rate has
reached a level predetermined by the patient's age. The echocardiogram is repeated at peak stress
and the patient is allowed to recover. Heart images obtained before stress are then compared with those
obtained at peak stress, using a computer to display the pictures in a side-to-side fashion. In brief,
healthy heart muscle will appear to squeeze normally at rest and get stronger with exercise. Heart
tissue that has been damaged by a previous heart attack may not squeeze at all at rest or with stress.
In some cases however, the heart tissue is simply starved but not permanently damaged. In these
situations, the heart tissue will appear weak at rest, get stronger with low levels of stress, then
again as stress increases. All of these changes can be readily seen on the echocardiograms.
How long does it take? The stress echocardiogram includes at least two complete studies of the heart
as well as the stress test. It usually takes about an hour to obtain all of this information. On
the bright side, the physician supervising the examination can often interpret the study immediately
and give the patient the results before they leave the office.
What does the patient feel? In order to get the echocardioraphic pictures, the technologist will
have the patient undress from the waist up and usually have them put on a gown. Wires to an
echocardiogram monitoring machine will be stuck on the patient's chest. A water-soluble gel is
used to get a good connection between the echocardiogram imaging probe and the patient's chest.
Unfortunately, this usually feels cold. How the patient feels next depends on how their heart is
stressed. If they walk on a treadmill, they will feel tired, breathless, and perhaps experience
chest discomfort. If dobutamine is used, an IV needle will be inserted into the patient's arm.
The dobutamine usually causes the patient to feel palpitations, shortness of breath and possibly
some anxiety or chest discomfort. The dobutamine is usually given for 15-20 minutes and wears off
within an additional 10-15 minutes.
What are the advantages of a stress echocardiogram? For many patients, a standard stress test
without any pictures of the heart is adequate. If the patient's baseline electrocardiogram is
abnormal, however, a routine stress test may not be diagnostic and an imaging test like the stress
echocardiogram is essential. In addition, the routine stress test is notoriously unreliable in
women where false test results are common. Stress echocardiography is able to accurately assess
both women and men. Finally, additional information such as heart strength and valve function is
easily attainable with stress echocardiography but not with a standard stress test.
Is it dangerous? Routine stress tests are very safe for the diagnosis of coronary disease. The risk
of a serious complication in the general population is less than one chance in 2000. The
addition of echocardiography to the exam does not increase the risk. An exercise test should not
be done in patients with acute unstable angina, uncontrolled arrhythmias, uncompensated heart failure,
critical aortic stenosis, severe obstructive hypertrophic cardiomyopathy, or controlled
hypertension in order to keep risk at a minimum. If dobutamine is used to stress the heart, the
risk of serious complication is somewhat higher (about 3 chances in 1,000 of a serious side effect),
but still quite low. Certainly the risk of complications with undiagnosed or misdiagnosed
atherosclerosis is much higher.
Conclusion? Stress echocardiography is a versatile test for safely and accurately evaluating
coronary heart disease including its risks and complications. It can be performed in a wide variety
of patients in the cardiologist's office or at the patient's hospital bedside. It does not require
the use of radioactive isotopes or x-rays and can often be done without even inserting an IV into
the patient, yet it provides an enormous amount of information about heart structure, function,
and blood supply.
