Wednesday, February 8, 2012

The LAD occlusion formula did not work here. Why?

I received this from a reader, who applied the LAD occlusion (anterior STEMI) formula.

The patient presented with chest pain and dyspnea.  Here is his ED ECG.

There is anterior ST elevation, so they were worried about STEMI. The QTc was 429 ms.  ST elevation at 60 ms after the J-point is 4.5 mm.  R-wave amplitude in V4 is 14 mm.  The formula value is 26.1 (>23.4), suggesting anterior STEMI.

What do you think about this ST elevation?








I received this from a reader as a possible false positive case because he ruled out for MI by troponins and echo.

This, however, is a case of LVH on the ECG.  There is high voltage and the typical repolarization abnormalities of LVH, with the "hockey stick" ST depression (formerly called "strain") in I, aVL, V5 and V6, and the very high S-wave voltage in the leads with ST elevation (V3 = 3mm at J-point, and 4.5 mm at 60 ms after the J-point).  However, this is an expected amount of ST elevation for such a large preceding S-wave.

The formula was not derived using a control group with LVH, and does not work for LVH.  It is only to be applied when differentiating normal variant ST elevation (early repolarization) from anterior STEMI.

(It is also important to remember that the sensitivity and specificity of the formula was not perfect, at about 90% and 90%)

I am working on a formula for differentiating the ST elevation of LVH from that of anterior STEMI.  It will involve a ratio of ST Elevation to preceding S-wave.  We have a large group of LVH patients, some with and some without STEMI, whom we are comparing.

One thing I hypothesized based on my experience, and that we are indeed finding in our data, is that when there is LVH on the ECG with large S-wave amplitude, the patient almost never has a STEMI!  This is because those who do have LVH with a large S-wave amplitude lose that amplitude when the LAD is occluded!!!

5 comments:

  1. Dr Smith,
    I find it interesting that the S-wave amplitude decreases in the setting of LVH and LAD occlusion, do you know or have any theories as to why this occurs?
    Thanks

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  2. The ischemia keeps the ventricle from fully depolarizing as it normally does. That's my theory.

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  3. I've seen a few LVH's called in as possible "Code STEMI" en route to the ED. It's an important DDX to recognise - if only to save face in front of the cardiologists!
    Cheers
    Chris Nickson
    http://lifeinthefastlane.com

    ReplyDelete
  4. In example #1, does how much depression matter? What about mild depression in said leads?

    ReplyDelete