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.

Let’s take another look at the 12-lead ECG.

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

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Comments
Erik
What If We’re Wrong? Prehospital ECG Interpretation
In my paramedic class we were taught to pay attention to the numbers generated by the monitor, but you can never trust them. You must examine the rhythms in each lead and look for appropriate elevations along with reciprocal depressions. And this is not a time consuming event. I will say that in my city…
2015-08-05 01:13:26
EMS Artifact
Nitro paste is NOT an emergency medicine drug – The Evidence
Interesting post. As you point out, nitropaste is ineffective in treating acute CHF. Of all the treatments I used over the years for this, CPAP is by far the best. That is followed by NTG spray, which my system started using in the late 1980s when it was first available. Our protocol then (and now)…
2015-08-05 00:22:18
michelle
68 Year Old Male: Chest Tightness – Part 1
i see some depression and slight elevation in the st segment in the avr. i would alert the stemi crew to stand by.
2015-07-27 17:15:03
sean morrison
68 Year Old Male: Chest Tightness – Part 1
It's the big one Weezy! LAD
2015-07-27 12:48:03
Ryan Lord
68 Year Old Male: Chest Tightness – Part 1
Had the exact same last night but a known AF patient pain commenced after 2 hours of palpitations and described as like a previous MI. Her rate was up at around the 160 mark... Had the widespread depression but elevated aVR and V1. Discussed with Cath Lab and preceded to A&E next door for review,…
2015-07-27 12:14:23

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