STRESS TESTING – A PATIENT GUIDE
WHAT IS A STRESS TEST ?
Persons with heart artery blockages may have minimal or no symptoms at rest. However, symptoms of underlying blockages may occur during stress. Stressing the heart can be done by exercise or by using medicines that stimulate the heart. During exercise, healthy heart arteries enlarge to accommodate increased blood flow. Narrowed arteries are unable to compensate for increased blood flow needed during exercise. This compromises blood flow to the heart muscle resulting in heart muscle being “starved” of oxygen.
This “starvation” can result in
- Symptoms such as chest discomfort or shortness of breath
- ECG abnormalities
- Reduced contraction of the heart muscle supplied by the narrowed coronary artery. This can be detected by using a specialized ultrasound investigation called echocardiography.
- Reduced functioning of heart muscle cells. This can be detected by a special investigation called a nuclear or “MIBI” scan
ECG changes during exercise can often produce false results. The ability to evaluate heart contraction or heart muscle cell function therefore produces more accurate results. As such, the use of nuclear scanning or echocardiography is more precise than the traditional use of ECG based exercise testing.
Echocardiography has the advantage of being completely radiation free. There is also the ability to evaluate the structure of the heart such as the muscles, valves and chambers. This is not possible with nuclear or ECG stress testing.
HOW IS STRESS ECHOCARDIOGRAPHY PERFORMED ?
A Stress Echocardiography test is conducted as an outpatient and does not require hospitalization.
A “resting” study is first performed with the person lying down. This provides a baseline examination, from which information regarding the size and function of the various chambers of the heart and structure and function of the valves may be obtained. Electrodes are attached to the chest and connected to wires to record the electrocardiogram (ECG).
A colourless gel is then applied to the chest and the Echo transducer is placed on top of it. The Cardiologist then makes recordings from different parts of the chest to obtain several views of the heart. The patient may be asked to move from the back to the left side. Instructions may also be given for the patient to breathe slowly of to hold their breath in order to obtain clear pictures of the heart.
Exercise is then initiated using a treadmill. In persons who are unable to complete a high level of exercise, stress to the heart is provided by medicines infused through an IV line inserted into the vein of an arm.
The initial stage is a warm-up phase and is done very slowly. The speed of the treadmill and slope is then increased every three minutes. The treadmill is stopped when the person exceeds 85% of the target heart rate (based upon person’s age). Exercise may be stopped earlier if the person develops symptoms such as chest discomfort, marked shortness of breath, weakness or dizziness. A Cardiologist would be in attendance throughout the test and the above problems are uncommon.
Immediately after the treadmill, the person moves directly to the examination bed and lies on the left side, where the Echo examination is immediately repeated.
By comparing the rest images with the post-exercise images the Cardiologist would look for any abnormalities in how the heart muscle contracts in response to exercise. Normally, exercise would result in a significant increase in heart muscle contraction. Reduced heart muscle contraction during exercise indicates the presence of blockages in one or more heart arteries. Depending on the severity of the abnormalities detected, further evaluation by Coronary Angiography may be indicated.
HOW SAFE IS STRESS ECHOCARDIOGRAPHY?
There are no known adverse effects from the ultrasound used during Echo imaging. The risk of the stress test is similar to the risks involved in any strenuous form of exercise. A Cardiologist would be present throughout the test to manage any rare complications that may occur. These problems could potentially have occurred if the same person performed an equivalent level of exercise at home or in a gymnasium.
WHO SHOULD CONSIDER STRESS ECHOCARDIOGRAPHY?
Stress Echocardiography is capable of diagnosing significant disease in more than 85% of persons with significant heart artery narrowing.
On the basis of currently available information, Stress Echocardiography may be considered as a reasonable test in the following situations:
- Persons with symptoms suggestive of coronary artery disease
- Persons with unclear or inconclusive ECG treadmill test
- Persons with known heart disease in order to evaluate progression of the disease
- To assess heart attack risk for persons who are about to undergo major surgery
- To assess persons with chronic severe heart valve abnormalities
WHAT PREPARATION IS REQUIRED FOR STRESS ECHOCARDIOGRAPHY?
Stress Echocardiography is an outpatient test and does not require hospitalization. The whole procedure takes approximately 90 minutes.
The following steps are required:
- 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 their doctor.
- Specific heart medicines (e.g. beta-blockers) 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.