What is an Exercise Stress Test?
This is a well established and common cardiac investigation that has been in use for several decades and is used primarily in the evaluation of ischaemic heart disease. It is also known as Treadmill Exercise Stress Test. However, it is also conducted in the evaluation of a number of other cardiac problems.
A subject taking an exercise stress test (front)
Is the Treadmill Exercise Stress Test safe?
If patients are carefully selected for exercise testing, the rate of serious complications such as death or heart attack is low — about 1 in 10,000 tests (0.01 percent).
Abnormal heart rhythm may also occur during the test. Serious life threatening heart rhythm (ventricular tachycardia / fibrillation) may occur in about 1 in 5000 cases.
Your status is closely monitored throughout the test by your physician or trained technician to detect abnormalities during the test.
Why should I have the Treadmill Exercise Stress Test?
A person with coronary artery blockages may have minimal or no symptom. The resting ECG may also be normal. On the other hand, patients with NO heart disease may have alarming symptoms and a suspicious ECG.
Therefore if you have symptoms of known or suspected coronary artery disease (CAD) or an abnormal ECG, this test is commonly requested to assess the probability of disease.
Even if you have confirmed CAD, your physician may order the test for risk or prognostic assessment. Sometimes, it is ordered in the evaluation of persons with cardiac valvular diseases to determine the timing of surgery.
How is the Treadmill Exercise Stress Test done?
Just like a resting ECG test, sticky patches called ECG electrodes are placed on your chest. The electrodes transmit your heart electrical signals to the stress test machine. A wrap is placed around your waist to hold the cables in place.
During the test, the electrocardiogram machine provides a continuous recording of the heart rate and rhythm. A 12-lead electrocardiogram is recorded intermittently. Blood pressure is measured before the exercise begins and during each exercise stage.
The treadmill machine would increase in speed and its slope with incremental stages according to the test protocol. The test is continued until a target heart rate is achieved. This target is calculated based on your age. However, it may be stopped earlier if the person develops disturbing symptoms (e.g. chest pain, extreme shortness of breath, weakness, etc.), abnormal ECG changes or blood pressure readings.
A subject taking an exercise stress test (back)
How accurate is the Treadmill Exercise Stress Test?
Exercise testing has a sensitivity (ability to detect disease when it is truly present) of 70 percent and a specificity (ability to produce a negative result when there is no disease) of 70-80 percent for detecting coronary artery disease.
It is used to indicate the likelihood of ischaemic heart disease but the baseline/pre-test probability of disease has to be taken into account during interpretation of results. E.g. in a low risk population, such as men aged under 30 years and women aged under 40, a positive test result is more likely to be a false-positive one rather than truly abnormal, and negative results would add little new information. In a high risk population, such as those aged over 50 with typical angina symptoms, a negative result cannot absolutely rule out ischaemic heart disease, though the results may be of some prognostic value.
Exercise testing is therefore of greatest diagnostic value in patients with an intermediate risk of coronary artery disease. We must also remember that stress test only detects the severely obstructive (usually more than 70 percent) narrowings.
How long does the Treadmill Exercise Stress Test take?
The duration depends very much on the target heart rate and the time it takes to achieve it. In general, it would about 30 minutes from preparation to completion of test.
Who should avoid the Treadmill Exercise Stress Test?
The Treadmill Exercise Stress Test should not be done on selected groups of people as listed below:
In persons who cannot perform the test owing to physical disadvantages (e.g. Arthritis, lung disease, poor physical conditioning) or unable to achieve the target heart rate, a pharmacological stress test may be used instead. In this case, instead of doing physical exercise to ‘stress’ the heart, medications are injected to ‘stress’ the heart.
The treadmill ECG test can be combined with a scan (echocardiography) i.e., stress echocardiography to improve the sensitivity of the test to 85 percent and specificity to 77 percent.
What does it mean if my test is positive?
A positive result suggests the possibility of coronary artery disease (CAD). Your physician will interpret this test whilst taking into account the pre-test probability of disease. If there is a strong suspicion, more definitive tests eg. Coronary angiography may be advised.
Does a negative test mean that I am free from any heart disease?
Stress ECG test estimates the probability of disease. The specificity of this test (ie. likelihood of a negative test when one is truly free of disease) is about 70-80%. Therefore, a negative test does not rule out heart disease completely. Again, the interpretation of this test depends on your baseline probability of disease.
As mentioned, this test detects only severe coronary artery obstructions (>70%). As we know today, most heart attacks occur not from the severe narrowings but the mild to moderate ones. Hence, although it is a good test to screen for presence of CAD, there are limitations and it is never definitive.
Disclaimer: This is only general information. A doctor should be contacted if you need any medical advice or if medical decisions need to be made.