T waves are the most enigmatic waves in clinical electrocardiography . This is not a surprise , when you consider a tall T wave and a markedly inverted T wave both can be normal in at least in 6 leads out of 12 lead standard electrocardiogram ( V1 V2 V3 , 2 ,3 AVF, ofcourse the AVR )
Common T wave patterns that can either be physiological or pathological
- Tall T wave
- Inverted T WAVE
- Notched or Bifid T wave
- Biphasic T wave
* T wave polarity is strongly determined by the direction of QRS vector. Generally it should be on the same direction as QRS. In the presence of conduction defect or chamber hypertrophy this gets altered and is refered toa s secondary repolarisation changes . This has to be differentiated from primary biphasic T waves.
What is a biphasic T wave ?
A T wave which is inscribed on either side of baseline is called biphasic T wave .
Many of the normal persons can have a biphasic Twave.
A typical biphasic wave can be two types
- Terminal positivity
- Terminal negativity
Terminal negativity is more significant than terminal positivity , especially in CAD.
A terminal negativity especially in mid precardial leads would suggest ongoing ischemia in LAD territory .
This happens due to dispersion of repolarisation between endocardium and epicardium.
The other mechanism could be the altered ventricular gradient between QRS vector and T wave vector.
Why biphasic T waves are important ?
The biphasic T waves are known for dynamic change in polarity . It may either pull down the or pull up the adjacent ST segment . Prolonged QT interval is a closely related to the biphasic T wave.
Some times a U wave can be inscribed in such a way it may mimic a biphasic T wave. This is especially common in baseline bradycardia.
LVH is one of the common cause of biphasic T wave (Usually terminal positivity )
Biphasic T wave as mode of presentation of NSTEMI
Even though , ST depression is considered the dominant and classical theme of NSTEMI , It is now recognised NSTEMI has another mode of common presentation as biphasic T waves.
Dr.S.Venkatesan MD 