T Wave Alternans

What is T Wave Alternans?

T wave alternans refers to a noninvasive diagnostic test to help identify patients who are at risk of life threatening heart rhythm disturbances that can lead to cardiac death.

This test refers to a beat to beat variability in the timing or shape of T waves on the surface electrocardiogram (ECG) which is not visible to the human eye. Therefore high resolution sensors are used to detect subtle changes in the ECG.

Sudden cardiac death is the nation’s number one cause of death. Most people who suffer a cardiac arrest have an underlying, pre-identifiable, electrical disorder that puts them at risk. A good way to identify this is through the measurement of TWA, a beat-to-beat alternation of a patients ECG.

Who needs it?

Patients who need a TWA are those who are at risk of sudden cardiac death (SCD). Sudden cardiac death occurs in patients who have abnormal heart rhythms or arrhythmias.
 
Risk of SCD typically focuses on the presence of a few factors:
 
  • Reduced left ventricular ejection fraction (blood squeezed out from left heart chamber)
  • Left ventricular dysfunction
  • Ischemic cardiomyopathy
  • Left ventricular hypertrophy
  • Aortic stenosis
Reduced left ventricular ejection fraction is currently the primary determinate of Implantable Cardioverter Defibrillators (ICD’s), however; reduced ventricular ejection fraction lacks sensitivity.
 
TWA is a tool to help clarify the overall risk of arrhythmias, especially in patients who have known risks, but who fall into this ‘gray area’ in ICD eligibility.
 

How is it done?

TWA is performed during a treadmill stress test. The standard stress test can only identify the presence of clogged arteries, while the TWA test will identify subtle changes in electrical disturbances.

For TWA to be detected and measured at this microscopic level, the patient’s heart rate must be raised, usually by means of exercise on a treadmill.

This test is painless, noninvasive, and done on an outpatient basis.

Prior to the test, sensors are attached to the patient’s chest.


The patient begins to walk on the treadmill.

Once the patient’s heart rate reaches 90 beats per minute, the TWA test will begin.

After 2.5 minutes, the test is complete.