Friday, January 15, 2021

ECG Blog #184 (ECG MP-2) — Magical Lead 3- Lead aVL Relationship


Interpreting ECGs is a visual skill — but important ECG concepts are sometimes more effectively conveyed by a brief audio message. This is the purpose of this new feature I’ve added to supplement content on my ECG Blog posts. 

  • I illustrate today’s ECG Media Pearl with several tracings excerpted from other blog posts.





ECG Media PEARL #2 (2:15 minutes Audio): — relates to the "magical" mirror-image opposite relationship with acute ischemia between lead III and lead aVL.

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Figure-1: ECG obtained from a 54-year old man. No history was available. How would you interpret this tracing? (Excerpted from ECG Blog #171).



Figure-2: Focusing on the 6 limb leads from Figure-1 — Note how the mirror-image of the ST-T wave in lead aVL (within the light BLUE insert) — looks identical to the shape of the elevated ST-T wave in lead III (within the WHITE rectangle). Similarly, the mirror-image of the elevated ST-T wave in lead III (within the light BLUE insert) — looks identical to the shape of the inverted ST-T wave in lead aVL (within the WHITE rectangle). This all but confirms ongoing acute inferior MI (Full details of this case discussed in ECG Blog #171).


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Figure-3: ECG obtained from a man in his 50s with chest pain. Although the amount of ST elevation in leads I, aVL and V6 is not a lot — the reason we KNOW that this is an important real finding — is that the SHAPE of the ST elevation in lead aVL is the precise mirror-image opposite of the shape of the ST segment depression in lead III. (Excerpted from My Comment, which is found at the bottom of the page in the October 6, 2018 post in Dr. Smith’s ECG Blog. The mirror-image picture of the ST-T wave of lead aVL is within the GREEN rectangle; and the mirror-image of lead III is within the BLUE rectangle).



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