About Exercise Tolerance Test

An exercise tolerance test (ETT) is a type of electrocardiogram that records the electrical activity of your heart while you are exercising. An ETT is an important cardiac test as it can show how well your heart functions while under physiological stress.

Also known as a stress test or an exercise ECG, an exercise tolerance test can assess:

·      The electrical activity of your heart.
·      Your heart rate during exertion (for example, if it beats too slowly or too quickly).
·      The rhythm of your heart (whether it is regular or irregular).
·      The strength and timing of your heart electrical impulses.
·      How well the blood circulates around your heart.
·      The overall function of your heart.

Every time your heart beats,  electrical signals are formed in your sinus node(SAN), in the upper wall of your heart right atrium. The sinus node is the natural pacemaker of your heart, and it sets your heart rate and rhythm. Every time your heart beats, electrical signals travel through your heart, coordinating contractions in different areas of your heart. These electrical signals ensure that blood and oxygen flow around your heart correctly.

An exercise tolerance test measures the electrical signals and the electrical activity of your heart to assess the overall function of your heart while you are exerting yourself.

ETTs are primarily used to:

·      Detect coronary heart disease.
·      Determine safe levels of exercise and exertion if you have had a heart attack or heart surgery.
·      Assess the extent of limited blood supply to the heart in someone who is already diagnosed with coronary heart disease.
·      Evaluate how effective a current treatment is for someone who is already diagnosed with coronary heart disease.

When you exercise, your heart needs to work harder. The muscles of your heart contract faster and harder, your heart beats more quickly and the blood flow from your coronary arteries increases. An ETT allows your cardiologist to assess how well your blood flows through your coronary arteries while your heart is under stress.  

If you have coronary heart disease, this can cause a build-up of plaque, which is made up of fatty substances and cholesterol, in the walls of your coronary arteries (the arteries that supply blood to your heart). As plaque builds up over time, the inside of your arteries can become narrowed. This can restrict blood flow to your heart, meaning your heart won’t get enough oxygen-rich blood. You may then begin to experience symptoms of coronary heart disease, such as:

·      Chest pain (angina) or discomfort in your chest, including a feeling of pressure, heaviness or tightness. This pain can also spread to your left arm, neck, jaw, back or stomach.
·      Feeling dizzy or lightheaded.
·      Shortness of breath.
·      Sweating.
·      Heart palpitations.
·      A faster heart rate.
·      Weakness.

Many people with coronary heart disease have a normal heartrate during rest. When you are physically exerting yourself and your heart is under stress, the symptoms of coronary heart disease will then manifest, and an ECG will show abnormal results. The level of abnormality that is detected will indicate how severe the coronary heart disease is.

During an exercise ECG, any area of your heart that is lacking in oxygen will be shown on the ECG. This allows the cardiologist to see which coronary artery is blocked. For example, a lack of oxygen in the right ventricle indicates that the right coronary artery is blocked.

Over time, coronary heart disease can lead to your heart muscle becoming weaker. This could result in heart failure or a heart attack. This is why early diagnosis and treatment are key.

How to Prepare for An Exercise Tolerance Test

Before your ETT, there are certain guidelines you should follow to ensure a more accurate test:
·      Do not smoke for at least four hours before the test.
·      Do not eat for at least one hour before the test.
·      Ensure the last meal you eat is small and light.
·      Do not drink alcohol for at least 12 hours before the test.
·      Keep caffeine and sugar to a minimum.

If you take any medications, particularly for diabetes or other cardiac conditions, you should contact the cardiologist prior to the test to receive specific instructions regarding your medication. Certain types of medication may require you to adjust or reduce the dosage before an ETT.

What to Expect During an Exercise Tolerance Test

Your exercise tolerance test will take place in the clinic and will be managed and overseen by the cardiologist at all times. Electrodes, which look like small sticky patches, will be attached to your  chest and connected to the ECG machine. These electrodes will measure the electrical activity of your heart throughout the ETT.

You will need to wear comfortable clothing and trainers for the test. To assess your heart under stress, you will need to engage in physical activity, either on a stationary exercise bike or a treadmill. The test will begin with you exercising at a slow and comfortable pace, either by walking or cycling slowly. The difficulty of the test will gradually increase until you are exercising more strenuously.

The cardiologist will monitor you closely throughout the test. They may also take your blood pressure few times during the test. If you feel chest pain or become dizzy or are particularly short of breath, you can ask the cardiologist to stop the test at any time.

The ETT usually takes between 10 and 15 minutes, depending on how long it takes you to reach the desired heart rate. However, don’t be concerned if your test takes longer. The test will be stopped once acceptable diagnostic information is acquired or if your symptoms warrant the discontinuation of the test.

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