T Wave Alterans (TWA)
What is a TWA Stress Test?
The test examines the standard Electrocardiogram (ECG). T wave alternans is a change in the shape of the T wave on an every other beat basis (see arrows) that are not often apparent to the naked eye. These changes predispose patients to abnormal heart rhythms that can lead to sudden death. It is usually performed during an exercise stress test. Using sophisticated electronics, smart electrodes, and special software, the test can detect alternations of theT wave that are very small.
What is a TWA Stress Test used for?
The Microvolt T-Wave Alternans test is designed to help identify patients at risk of life threatening heart rhythm disturbances that can lead to sudden cardiac death.
What can I Expect?
- DO NOT eat or drink anything except water for 4 hours before the test
- DO NOT take the following heart medications on the day of the test unless your physician tells you otherwise or if the medication is needed to treat chest discomfort:
- Beta blockers [for example: atenolol (Tenormin),metroprolol (Lopressor, Toprol), Propranolol (Inderal)]
- Bring your medication with you on the day of the test. Your physician may also ask you to stop taking other heart medications on the day of the test.
- If you have questions about your medications — ask your physician. Do not stop any medication without first talking with your doctor.
- If you have diabetes and take medications to manage your blood sugar, ask your physician how to adjust your medications the day of your test. Do not take your diabetes medication and skip a meal before the test. If you own a glucose monitor, bring it with you to check your blood sugar levels before and after your test. If you think your blood sugar is low, tell the lab personnel immediately. Plan to eat and take your blood sugar medication after your test.
- If you use an inhaler for breathing, bring it to the test.
- Wear comfortable clothes. Bring shoes suitable for walking. You will need to change into a hospital gown to wear during the procedure. You will be given a locker to store your belongings during the test. Do not bring valuables.
- Before the test, a technician, nurse or physician will explain the procedure in detail, including possible complications and side effects. They will be available to answer any questions you may have.
- First, the technician will gently rub ten small areas of your chest, and place small sticky electrode patches to these areas. The electrodes are attached to an electrocardiograph (ECG) monitor, which charts your heart’s electrical activity during the test.
- Before you begin to exercise, the technician will perform a resting ECG, measure your resting heart rate and take your blood pressure.
- Then, you will exercise on a treadmill. The lab personnel will ask you to start exercising and gradually increase your rate of exercise. You will be asked to exercise to a mild to moderate level of exertion. It is normal for your heart rate, blood pressure, breathing and perspiration to increase. This information will allow your physician to assess your heart's ability to function.
- At regular intervals, the lab personnel will ask how you are feeling. If you feel chest, arm or jaw pain or discomfort, short of breath, dizzy, lightheaded, irregular heart beats or if you have any other unusual symptoms, tell the stress lab personnel immediately.
- The lab personnel will watch for changes on the EKG monitor that suggest the test should be stopped.
- Your heart rate, blood pressure and EKG will continue to be monitored after exercising until the levels are returning to normal.
The appointment takes about 60 minutes. The actual exercise time is usually between 7 and 12 minutes.
After the cardiologist reviews your test, the results will go into your electronic medical record. Your physician will have access to the results and will discuss them with you. Ask you doctor if you have any questions about the TWA Stress Test.
ABCD Trial (Alternans Before Cardioverter Defibrillator Trial)
Currently, the Heart and Vascular Center is the organizing and national coordinating center of a clinical trial testing the utility of the T wave alternans test. The trial compares the usefulness of TWA compared to invasive electrophysiology testing in identifying patients at highest risk for sudden death .