Module title = Tutorial: ACS Plus

Lesson title = The T wave

• orientation: upgoing, downgoing (inverted) or biphasic
• concordance with QRS
• morphology (size and shape)

Here is an example of an upgoing T wave. Upgoing T waves are normal:


That was boring.

This is a biphasic T wave. It has 2 "phases": this one has an initial downgoing deflection followed by an upgoing deflection.


The blue arrow indicates the inverted portion of the T wave. The red arrow indicates the upgoing portion of the T wave.

Here is another example of a biphasic T wave where the inverted portion is larger than the upright portion:


Biphasic waves are not normal. Biphasic T waves can be "up then down", or "down, then up". There are 2 causes of biphasic T waves:

• Ischemia 
• Hypokalemia

An inverted T wave looks like this:


Inverted T waves have many different causes and these will be explained in other lessons.

Inverted T waves are not normal. An exception to this rule is lead aVR: it normally will have an inverted T wave. aVR is like the lead that is "in reverse". It will often have waves that are the opposite direction compared to most other leads.

Concordance refers to the direction of the QRS compared to the direction of the T wave. If both the QRS and T wave are upgoing, then they are concordant. If they are both downgoing, they are also concordant. If one is going up and the other is going down, then they are discordant. Concordance is normal; discordance is not normal.

Concordant: both QRS and T wave are upgoing:


Concordant: both QRS and T wave are downgoing (this is common in aVR for normal ECG's):


Discordant: QRS is upgoing, T wave is downgoing:


Discordant: QRS is downgoing, T wave is upgoing:


Next, describe the morphology (size and shape) of the T wave. The T wave can be:

• peaked (tall and skinny)
• flattened

• more than 0.5-1 mV (which is 5-10 little squares, or 1-2 big squares on the ECG)¹

These peaked T waves in leads V_3-5 are suggestive of antero-lateral ischemia:


In a different patient, tall (peaked) T waves are seen in leads III and aVF, suggestive of inferior ischemia.  Note that the top of the T wave is higher than the top of the QRS in both leads.


Using the definition of a T wave > 0.5 mV (5 little squares), the T waves are peaked in leads V_3-6:


Here is a peaked T wave that is occurring during an acute myocardial infarction. These peaked T waves are referred to as "hyperacute T waves" when associated with an acute MI:


Flattened T waves are a non-specific finding, but may be caused by ischaemia or an electrolyte abnormality such as hypokalaemia. Flattened T waves due to ischemia are usually in a localized region of the ECG, while electrolyte abormalities cause T wave flattening in most or all leads.

Here is an example of flat T waves in V₁ (blue arrows) and simultaneous ST depression in V₄ and V₅ from ischemia (red arrows):


References:

1. Macfarlane PW, Lawrie TDV: Appendix 1: Normal limits, in Comprehensive Electrocardiography. New York, Pergamon, 1989, pp 1446-1457.