How a Stress Echo Works
Patients with coronary artery blockages may have minimal or no symptoms during rest. However, symptoms and signs of heart disease may be unmasked by exposing the heart to the stress of exercise. During exercise, healthy coronary arteries dilate (develop a more open channel) than an artery with a blockage. This unequal dilation causes more blood to be delivered to heart muscle supplied by the normal artery. In contrast, narrowed arteries end up supplying reduced flow to its area of distribution. This reduced flow causes the involved muscle to "starve" during exercise. This starvation may produce symptoms (like chest discomfort or inappropriate shortness of breath), EKG abnormalities and reduced movement of the heart muscle. The latter can be recognized by examining the movement of the walls of the left ventricle (the major pumping chamber of the heart) by Echocardiography.
How a Stress Echo is Performed
A Stress Echo can be obtained in a physician's office or in the hospital. Imaging tests are generally done when a physician wishes to confirm or rule out the presence of coronary artery disease. A Stress Echo is also performed in patients who have disease involving the heart muscle or valve, or if a patient is having inappropriate shortness of breath and a cardiac cause is suspected.
The patient is brought to the Echo laboratory where a resting study is performed. This provides a baseline examination and demonstrates the size and function of various chambers of the heart. Particular attention is paid to the movement of all walls of the left ventricle (LV). Similar to a regular echo test, sticky patches or electrodes are attached to the chest and shoulders and connected to wires to record the electrocardiogram (EKG or ECG). The EKG helps in the timing of various cardiac events (filling and emptying of chambers).
A colorless gel is first applied to the chest for conductivity and the echo transducer is placed on top of it. The echo technologist then makes recordings from different parts of the chest to obtain several views of the heart. The patient may be asked to move from her back and to her left side. Instructions may also be given to breathe slowly or to hold his or her breath. This helps to obtain higher quality pictures. The images are constantly viewed on the monitor. They are also recorded on photographic paper, video, and a computer.
Twelve leads of the EKG are recorded on paper and blood pressure is taken. Exercise is then initiated using a treadmill (most common) or a stationary bicycle. In patients who are unable to complete a high level of exercise because of physical limitations, stress to the heart is provided by pharmaceutical or chemical stimulation of the heart. Stress Echo is made up of three parts, a resting Echo study, a Stress test, and a repeat Echo while the heart is still beating fast.
Exercise stress testing usually employs the Bruceor a similar protocol, as described in the Regular Stress Test section. Exercise is started at a slower warm-up speed. The speed of the treadmill and its slope or inclination is increased every 3 minutes. The treadmill is abruptly stopped when the patient exceeds 85% of the target rate (based upon the patient's age). Exercise may be stopped earlier if the patient develops alarming symptoms (chest discomfort, marked shortness of breath, weakness, dizziness, etc.), if there is dangerous elevation or drop in the blood pressure, there are significant EKG changes, or a potentially dangerous irregular heart rhythm. Please remember that there is a physician in attendance (although an experienced assistant may perform the test if the physician is tied up with an emergency). The above problems are uncommon and the patient is much safer if they occur in the presence of an experienced medical team rather than while he or she is exercising in a gym, jogging, or running up a flight of office stairs.
EKG recordings are made during every minute of exercise and then again after the exercise is stopped. Blood pressure is recorded at three minute intervals during exercise and then again at rest. Immediately after stopping the treadmill, the patient moves directly to the examination table and lies on the left side and the Echo examination is repeated. Images are stored and then played back on the computer. A video clip of multiple views of the resting and exercise study are compared side-by-side and are analyzed by the physician. Normally, one expects an increased EF or ejection fraction (a measure of how well the heart is pumping), and the LV walls not to show any exercise-induced abnormal movement. In contrast, a drop in EF and/or a new wall motion abnormality is an indicator of disease.
Preparing for an Stress Echo Test
The following recommendations are generic for all types of cardiac stress tests:
- Do not eat or drink for three hours prior to the procedure. This reduces the likelihood of nausea that may accompany strenuous exercise after a heavy meal. Diabetics, particularly those who use insulin, will need special instructions from the physician's office.
- Specific heart medicines may need to be stopped one or two days prior to the test. Such instructions are generally provided when the test is scheduled.
- Wear comfortable clothing and shoes that are suitable for exercise.
- An explanation of the test is provided and the patient is asked to sign a consent form.
How Long Does a Stress Echo Test Take?
A patient should allow 1 1/2 to 2 hours for the entire test, including the preparation, echo imaging and stress test.
How Safe is a Stress Echo?
There are no known adverse effects from the ultrasound used during Echo imaging. The risk of the stress portion of the test is rare and similar to what you would expect from any strenuous form of exercise (jogging in your neighborhood, running up a flight of stairs, etc.). As noted earlier, experienced medical staff is in attendance to manage the rare complications like sustained abnormal heart rhythm, unrelieved chest pain or even a heart attack. These problems could potentially have occurred if the same patient performed an equivalent level of exercise at home or on a jogging track.
What is the Reliability of a Stress Echo?
If a patient is able to achieve the target heart rate and if the Echo images are of good technical quality, a Stress Echo is capable of diagnosing important disease in more than 85% of patients with coronary artery disease. Also, it can exclude important disease in more than 90% of cases when the test is absolutely normal.
How Long Does it Take to Get Results and What Do They Mean?
The physician conducting the test will be able to give you the preliminary results before you leave the Stress Echo laboratory. However, the official result may take a few days to complete. The results of the test may help confirm or rule out a diagnosis of heart disease. In patients with known coronary artery disease (prior heart attack, known coronary blockages, previous treatment with angioplasty, stents or bypass surgery, etc.), the study will help confirm that the patient is in a stable state, or whether a new blockage is developing. The results may influence your physician's decision to change your treatment or recommend additional testing such as cardiac catheterization.