[SCD-FORUM] 119E microvolt T- wave alternans Dr. Roy

[SCD Symposium]

Dear Dr. Vera Komoliatova

Micro wave T wave alternans and ST segment variability are not the same.

      A fluctuation in morphology of the T- wave during alternating beats
is called T-wave alternans (TWA). These subtle alternations are
usually not apparent on the surface ECG, but can be measured by
several signal processing techniques which amplifies the signals in
microvolt level (Microvolt TWA). The alternations in T wave
morphology are reflective of physiologically important abnormalities
in repolarisation present on microvolt level. MTWA are linked to
electrical instability of the heart and they are predictive of
ventricular arrhythmias.

      Spectral analysis during controlled heart rate acceleration is the
most widely applied technique to measure TWA. The test is performed
with seven standard stress test electrodes and seven electrodes
which have multisegment microvolt alternans sensors on an exercise
stress test machine. We use Cambridge Heart Inc CH 2000 for this
purpose which uses FFT spectral analysis. The magnitude of TWA is
strongly dependent on heart rate and optimal rate for measuring MTWA
is between 100 to 120 beats per minute.
T-wave alternans is simpler and briefer than a standard exercise test done
to detect myocardial ischemia.
      Recently studies of microvolt T-wave alternans have shown great
promise as a second tier of risk stratification in patients with
left ventricular dysfunction. This test has very high negative
predictive accuracy. T-wave alternans tests are non-invasive,
inexpensive, safe, work equally well in ischemic and non-ischemic
left ventricular dysfunction, and have very high negative predictive
accuracy and the automated reading gives excellent results.
Measurements of MTWA may be inaccurate in patients who have not
withheld beta blockers and who have persistent atrial fibrillation
or flutter and the contraindications are same as for a standard
exercise stress test.

Dr. Sunil Roy T.N
E mail: sunilroytn at calicutmedicalcollege.ac.in