ECG Level 3 Tutorial: ACS Plus
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Tutorial: ACS Plus
Learn diagnostic criteria for Acute Coronary Syndromes, as well as other diagnoses that could be confused with them: early repolarization, pericarditis and non specific ST-T wave changes.
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Tutorial: ACS Plus The T wave
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1h 24m
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1m 24s
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The T wave
The T wave should be analyzed after the ST segment. The T wave should be analyzed for:
  • 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:
upgoing T wave

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.
biphasic T wave

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 T wave

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 wave

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 T wave

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

Discordant: QRS is upgoing, T wave is downgoing:
discordant T wave

Discordant: QRS is downgoing, T wave is upgoing:
discordant T wave

Next, describe the morphology (size and shape) of the T wave. The T wave can be:
  • peaked (tall and skinny)
  • flattened

There is more than one definition for a peaked T wave. Peaked T waves are tall (and usually a bit skinny), but the exactly how tall a T wave needs to be to be considered "peaked" is variable. A T wave height is often correlated with the height of the QRS: a bigger QRS = a bigger T wave. T waves are bigger in males and get smaller with age. One definition is:
  • 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 V3-5 are suggestive of antero-lateral ischemia:
peaked T waves

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.
tall T waves

Using the definition of a T wave > 0.5 mV (5 little squares), the T waves are peaked in leads V3-6:
peaked T waves

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):
ST segment elevation


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