How does Stress Echo work?
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 it's area of distribution. This reduced flow causes the involved muscle to "starve" during exercise. The "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 is a Stress Echo performed?
Imaging tests are generally obtained 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 electrodes or 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 then applied to the chest and the echo transducer (as described in the Echocardiogram section) 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. You may be asked to move form your back and to the left side. Instructions may also be given for you to breathe slowly or to hold your breath. This helps to obtain higher quality pictures. The images are constantly viewed on the monitor. It is also recorded on photographic paper, on videotape and on a computer disk. Exercise stress testing usually employs the "Bruce" or 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 it's 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, significant EKG changes or a potentially dangerous irregular heart rhythm. Please remember that you have 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 you are far safer if they occur in the presence of an experienced medical team rather than having them happen while you are exercising in a spa, jogging, or running up a flight of office stairs. EKG recordings are made during every minute of exercise and then again after exercise is stopped. The 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 lays on the left side. The Echo examination is immediately repeated. Images are stored and then played back by the computer. A video clip of multiple views of the resting and exercise study are compared side-by-side. They are analyzed by the physician. Normally, one expects an increased EF or ejection fraction (a measure of how well the heart is pumping). Also, the LV walls do not 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 the Echo Stress 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.
- 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 the entire 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 test?
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.
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