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

5 Comments

12 Trackbacks

Leave a Reply

Your email address will not be published. Required fields are marked *

EMS 12-Lead

Cardiac Rhythm Analysis, 12-Lead ECG Interpretation, Resuscitation

JEMS Talk: Google Hangout

Comments
Dominic
How to be successful at IV therapy – some advice for paramedic students
I learned from one of my field instructors to squeeze the arm on the opposite side of the insertion site rather than using your thumb to hold the vein straight/still. When you use your thumb you are more prone to not being able to drop the catheter to a proper angle, after flash, in order…
2015-09-03 20:10:24
iliyas
Masters Case #01: 50 Year Old Male – Severe Chest Pain
Short runs of V.T LAD LAHB Widespread st depression with St elevation in avr Lf msin / three vessle disease Not sure about rhythm
2015-08-26 06:34:44
Darren Earley
Masters Case #01: 50 Year Old Male – Severe Chest Pain
1. L.A.D 2. De Winters (ST Elevation aVR, ST abnormality V2-3). 3. Non sustained VT 4.Poor quality ECG so cannot say about p waves or whether A.fib. Pre alert for ppci = evolving occlusion of LAD artery. Aspirin. Pain relief. Diesel
2015-08-25 17:26:50
michelle
Masters Case #01: 50 Year Old Male – Severe Chest Pain
first pt. sat's are to low at 94% for just room air pt. needs hi-flow o2 at 15 lt. min. i see a-fib. with runs of 3. st depression. there is also a chance of pheumonia. after o2 administer fluids, a chest x-ray, monitor the heart and ekg especially where bp is low.
2015-08-25 16:57:39
Ivan Rios
Understanding Adenosine (Adenocard)
Correct, even for stress test, with the same purpose.
2015-08-18 17:07:24

ECG Medical Training

12-Lead ECG Challenge Smartphone App

Photobucket

12-Lead ECG Challenge Smartphone App - $5.99

  • Apple iOS
  • Android
  • Amazon
  • Web Based

  • FRN-TV video review
  • iMedicalApps.com review
  • Interested in Resuscitation?

    Interested in Advanced Cardiac Life Support?

    FireEMS Blogs eNewsletter

    Sign-up to receive our free monthly eNewsletter

    Visitor Map / Stats

    Locations of visitors to this page


    LATEST EMS NEWS

    HOT FORUM DISCUSSIONS