An exercise tolerance test (ETT) is an important diagnostic and prognostic cardiac test. It is a type of electrocardiogram (ECG) test that is used to assess the electrical activity of your heart while you are under physiological stress. Often called an exercise ECG or a stress test, an ETT measures your heart rate, your heart rhythm and the electrical activity of your heart, while you are exerting yourself.
As part of the ETT, you will be asked to exercise on a treadmill or an exercise bike. When you exercise, your heart muscles contract faster and harder, your heart beats faster and your coronary blood flow increases. During the ETT, the cardiologist will assess the electrical activity of your heart during exercise. This allows them to determine how well your blood flows through your coronary arteries (the arteries that bring blood and oxygen to your heart). An ETT can determine whether your heart functions properly when under stress.
Standard ECGs assess your heart electrical activity at rest. Many types of coronary heart diseases display no abnormalities on an ECG whilst you are resting. Having a standard ECG may therefore not detect any abnormal activity and a potentially life-threatening condition can go undiagnosed.
If your coronary arteries have narrowed, as a result of coronary heart disease, parts of your heart or your heart muscle may not be getting enough oxygen. Because your heart is under extra stress when you exercise, the additional pressure on your heart is more likely to be detected during an ETT, compared to other cardiac tests.
An ETT may have been recommended if:
· You have experienced symptoms consistent with coronary heart disease, but an ECG showed no abnormalities.
· You report that your symptoms worsen, or mainly manifest while you are exercising.
· If you have fainted during exercise.
· Your cardiologist wants to assess whether your existing heart treatments are working correctly and are effective.
· You need to determine how your heart functions under stress to determine safe levels of exercise.
An exercise tolerance test assesses:
· The overall function of your heart.
· How well your heart functions during exercise and stress.
· How well your blood circulates within your heart.
· Whether your heart receives enough oxygen during exertion.
· Whether there are any concerning changes in the electrical activity of your heart.
· Your heart rate during exertion.
An exercise tolerance test can show whether any heart rhythm abnormalities are brought on by exertion. This type of cardiac test is usually used for the detection of coronary artery disease, a group of cardiac diseases characterised by the narrowing of coronary arteries. If your coronary arteries are narrowed, your heart muscle may not be getting enough blood and oxygen, particularly when you are physically exerting yourself.
The ETT can show how well your heart functions under stress. By measuring your heart electrical activity, your cardiologist may be able to detect an arrhythmia, which is an irregular or abnormal heart rhythm, and a reduction in cardiac blood and oxygen flow, both of which indicate coronary artery disease.
Because you will be engaging in physical activity, you should wear comfortable clothes and trainers for your exercise tolerance test. To measure the electrical activity of your heart, small electrodes will be attached to your chest and then connected to an ECG machine.
You will either be asked to walk on a treadmill, initially at a slow pace before the incline or speed is steadily increased. Alternatively, you will be asked to cycle on an exercise bike, increasing the speed and difficulty as directed. The exercise is designed to become more strenuous to increase your heart rate. You will then be encouraged to run or cycle as hard as you can to increase the stress on your heart. This allows the cardiologist to assess your cardiac function during physical exertion.
Your heart rate, breathing and blood pressure will be monitored throughout the test to ensure they do not rise to a dangerous level. However, ensure you tell the doctor if you begin to feel chest pain or other concerning symptoms.
The time it takes to perform an exercise tolerance test can vary, depending on:
· The time it takes to steadily increase the intensity of the exercise, to the desired level.
· The time it takes for your heart rate to increase to the desired rate.
On average, an ETT takes between 10 and 15 minutes, but do not be concerned if yours takes longer than this.
Exercise tolerance tests are extremely safe, painless and non-invasive. There are rarely any complications or side effects to the test.
However, it is important to note that there is a small risk of complications such as ischaemia, arrhythmia, excessively high or low blood pressure or a heart attack occurring. These side effects can occur because of the stress placed on your heart during exercise. However, the risks are extremely low, and you will be constantly monitored throughout the test. Both you and the cardiologist can choose to stop the test at any time.