Excessive discordance as a marker of acute STEMI in LBBB

This is Part I of the conclusion to 80 year old male CC: Chest pain.

As we have discussed on numerous previous occasions, the expected relationship between the QRS complex and the ST-segment and T-wave in the setting of left bundle branch should be one of discordance.

This is sometimes referred to as the rule of appropriate T-wave discordance.

That means that in the setting of left bundle branch block, negatively deflected QRS complexes can be expected to show ST-elevation and upright T-waves.

Positively deflected QRS complexes can be expected to show ST-depression and inverted T-waves.

That's why left bundle branch block is an anterior STEMI mimic.

It is normal for the ST-segments to be deflected opposite the S-waves in the right precordial leads (V1-V3).

However, there is a limit to how much discordance is appropriate.

Sgarbossa's criteria requires at least 5 mm of discordant ST-elevation in order to be significant.

However, this criterion is problematic because it does not take into account the rule of proportionality.

That's why it's the weakest of Sgarbossa's critiera.

Discordant ST-elevation of 5 mm (as a stand-alone finding) only indicates a 50% probability of AMI according to Sgarbossa's original scoring algorithm.

 

This ECG from a previous case post demonstrates the dilemma.

 

The ST-elevation in leads V1-V3 is well over 5 mm but the S-waves are so deep that they are running off the bottom of the ECG paper.

This patient was not experiencing acute STEMI.

Stephen Smith, M.D. (of Dr. Smith's ECG Blog) uses a modified criterion which considers the ST/QRS ratio.

He has found that when the ST-segment is deviated more than 0.2 the QRS complex it is both a sensitive and specific marker for acute STEMI in the setting of left bundle branch block (and probably also paced rhythm).

(Note: This has since been revised to 0.25 the QRS (download PDF here). However, I still think it terms of allowing 1 mm of ST-elevation for every 5 mm of S-wave depth. When I do this, I round up. In other words, if the S-wave is 18 mm deep, I round up to 20, which means that I would allow up to 4 mm of ST-elevation in that lead.)

Let's examine each of these QRS complexes separately.

We'll start with the positively deflected QRS complex marked 'A'.

As you can see, the R-wave measures 10 mm. The J-point (relative to the PR segment) is depressed 3 mm. Therefore, the ST/QRS ratio is 0.3 (which is higher than 0.2). Hence, this finding would strongly suggest acute STEMI.

Now let's look at the negatively deflected QRS complex marked 'B'.

In this example the S-wave measures 10.5 mm. The J-point (relative to the PR segment) measures 3.5 mm. Therefore, the ST/QRS ratio is 0.33 (which is higher than 0.2). Hence, this finding, would strongly suggest acute STEMI.

In Part II we'll apply Dr. Smith's decision rule to the our recent case study.

See also:

80 year old male CC: Chest pain

80 year old male CC: Chest pain – Conclusion

Discordant ST-segment elevation in LBBB or paced rhythm

62 year old male CC: Chest pain

58 year old female CC: Chest pain

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EMS 12-Lead

Cardiac Rhythm Analysis, 12-Lead ECG Interpretation, Resuscitation
Comments
Mary
“Bad heartburn” – 82 y.o. female without chest pain.
I, for one, would really like to read a response or two, to Dr. Walsh's question to BV about why give atropine at this time. Why give atropin at this time? Thanks.
2014-08-23 13:14:19
“Bad heartburn” – Conclusion | EMS 12 Lead
63 year old male CC: Substernal Chest Pain – Discussion
[…] upright T waves is actually not representative of acute occlusion – for more on this, read this discussion on old versus “new” teaching on recognizing posterior MIs. We do not see ST elevation in aVR or V1 that would suggest a concomitant RV infarct, […]
2014-08-22 16:49:18
Brooks Walsh MD
“Bad heartburn” – 82 y.o. female without chest pain.
Why give atropine at this time?
2014-08-22 15:42:18
Bryan Laviolette
“Bad heartburn” – 82 y.o. female without chest pain.
In addition to the above treatment consensus (ASA, Plavix, judicious NTG, fentanyl, fluid bolus, right sided leads), I would absolutely transport this patient to a PCI centre. Culprit artery is the RCA (STE lead III > II) leading to AV nodal ischemia and junctional bradycardia. In addition to the above treatment I would give 0.5…
2014-08-22 13:14:35
Jared
“Bad heartburn” – 82 y.o. female without chest pain.
Not much to add but my 2 cents...I'd definitely be careful with the nitro, not saying withhold it completely but absolutely use some common sense. I'd have to say probably RCA occlusion, and catch team needs to be activated for a stemi alert immediately. Treat it like a stemi until proven otherwise. If it walks…
2014-08-22 08:49:36

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