Exercise Tolerance Testing

The ETT can be used to investigate coronary heart disease (sometimes called coronary artery disease). This disease is due to narrowing of the coronary arteries. It can cause a type of chest pain called angina as well as other problems. People who develop chest pain may be advised to have an ETT to help clarify the cause. However, newer investigations (eg, coronary angiography or myocardial perfusion scintigraphy) are now often used to diagnose coronary heart disease so exercise tolerance tests are less common, though they are still used.

Many people with coronary heart disease have a normal ECG at rest. During exercise the heart beats faster and needs more oxygen. If one or more of the coronary arteries are narrowed reducing the blood flow, some areas of the heart muscle do not get enough oxygen. This can cause the ECG tracing to become abnormal on exercising. A positive ETT (an abnormal reading) suggests that coronary heart disease is likely.

In people with known coronary heart disease, the degree of abnormality on the ECG tracing from the ETT can give an idea of the severity of the disease.

How is an exercise tolerance test done?

Small electrodes are stuck on to the chest. Wires from the electrodes are connected to the electrocardiogram (ECG) machine. A treadmill or an exercise bike is then used. The exercise starts at a very easy pace, and is gradually made more strenuous by increasing the speed and incline of the treadmill, or by putting some resistance on the bike wheel.

Whilst walking on the treadmill or cycling on the bike, ECG tracings are made and blood pressure will also be measured from time to time. The test lasts about 15-20 minutes.

What should I do to prepare for the test?

It is best to avoid a heavy meal within one hour of the test. Otherwise, there is no special preparation needed. For the test, wear loose-fitting clothes and shoes that are comfortable to walk in. Usual medication should be continued unless advised otherwise.

Limitations

An exercise tolerance test (ETT) is a valuable investigation but it is not 100% accurate. Sometimes tracings show changes during exercise, even though the person has a completely normal heart. Also, some people with coronary heart disease have a normal ETT with no changes on the tracing. Cardiologists are aware of this and use the results of the test in conjunction with other information such as symptoms and other test results.

Nowadays it is common for scans of the heart to be done rather than an ETT. The scans that can be done for the heart include:

• A cardiac magnetic resonance imaging (MRI) scan of the heart.

• A computerised tomography (CT) coronary scan - also called CT coronary angiography.

• A myocardial perfusion scan.

• A dobutamine stress echocardiogram, where a drug is used to mimic the effects of exercise and a scan of the heart can be done at the same time.

Risks

An ETT is done without any problems in the vast majority of cases. In people without coronary heart disease, complications are rare. However, serious complications can occur in a small number of people who have coronary heart disease. There is a small risk of developing a heart attack (myocardial infarction) or a serious heart irregularity (an arrhythmia) during the test. Medical help is near to hand to deal with possible problems