DSAE STEMI Review, Mod 2: Terminal QRS Distortion & the ST Segment


In this section, we will compare four tracings

Please refer to the ECG below as an example of a Classic Normal ECG.  Let us focus on the terminal portion of the QRS complexes.  Specifically, I want you to note the following:

  • The right-most precordial leads V1, V2, V3 take on an rS configuration (r << S)
  • The left-most precordial leads V4, V5, V6 take on a qR configuration (q << R)

Sometimes during the evolution of the acute Anterior STEMI, you will see the terminal S-wave begin to rise toward the baseline.  When the terminal S-wave rises above the baseline then it technically is no longer an S-wave.  When this occurs it is described as “terminal QRS distortion”.  This is highly suspicious of the Acute STEMI(this holds especially true of Leads V2, V3).

NOTE : An exception to this rule occurs when the take off of the J-point forms the shape of a “fish hook”  (J-wave)—–if this J-wave is present, the probability  shifts in the direction of a benign normal variant.

The rising of the nadir of the S-wave is demonstrated in the Illustration below:


Similarly if the QRS complex takes on a qR configuration, you might observe the following phenomena.  As the acute STEMI evolves, the J-point take off will rise with time.  When the J-point rises to > 50% the R-wave height it is called “terminal QRS distortion”.

This is highly suspicious of the acute STEMI(this holds especially true of Leads V5,V6)(the exception again occurs if a J-wave is present).  This rising of the J-point is shown schematically in the Illustration below.


We will now compare four tracings using the following chart (see below chart for ECG Tracings).

Tracing #1.a Hour “0”

Tracing #1.b. – at “1.5” hours evolving STEMI (same patient)

Tracing #2 – Early Repolarization (Benign Normal Variant)

Tracing #3 – Normal ECG

Conclusion:  When faced with the challenge of deciding whether a given tracing is early repolarization or acute STEMI (especially if the changes are subtle).  Look for “terminal QRS distortion”.  If present, it is highly suspicious for the Acute STEMI.