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 old 3 variable 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 old 3-variable 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.

The new 4-variable formula also has a falsely elevated value at 19.56 (greater than most accurate cutpoint of 18.2) in spite of the fact that it accounts for large QRS voltage in V2 (25 mm)

(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!!!

7 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

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

    ReplyDelete
  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
  5. Great post. I would like to do some comentary about that. Firt, The rhythm is sinus at 86-90/minute. Second, the intervals — the PR interval is normal and the QRS complex is narrow. Peguero Criteria = Deepest S in any chest lead + S in V4 ≥28 mm in man and ≥23 mm (~ 40 in V3 + 22 in V4 = 62 mm!). There are asymmetric (slow downslope and more rapid upslope) ST-T wave depression of strain in lead I, aVL and V5-V6. There are a obvious LVH, therefore the formula ((1.062 x STE at 60 ms after the J-point in V3 in mm) + (0.052 x computerized QTc) - (0.151 x QRSV2) - (0.268 x R-wave Amplitude in V4 in mm) may not apply in this ECG. Finally, Why the P wave in lead III is inverted?
    Anderson Santos from Brazil.

    ReplyDelete
    Replies
    1. Thank you Anderson! The reason the P in lead III is inverted (and especially why the P in lead I is taller than the P in lead II) — is that there is LA-LL Lead Reversal (that had not been detected). STAY TUNED — as I plan to illustrate this soon in a new Blog post — :)

      Delete

DEAR READER: We welcome your Comments! Unfortunately — due to a recent marked increase in SPAM — we have had to restrict commenting to Users with a GOOGLE Account. If you do not yet have a Google account — it should not take long to register. Comments give US feedback on how well Dr. Smith’s ECG Blog is addressing your needs — and they help to clarify concepts of interest to all readers. THANK YOU for your continued support!

Recommended Resources