Conclusion to Snapshot Case: 44 Year Old Male – Chest Tightness

This is the conclusion to the Snapshot Case located here. You may want to review the initial description again.


As many readers correctly pointed out, this patient is experiencing a STEMI.

2014.02.03 - 0000 - 01 - Bojana Uzelac - Blog Case - EMS 12-Lead

Let's start with the basics and work our way up to some pretty advanced topics.

First, there is anterior ST-elevation with upwardly-concave T-waves, as known as smiley-face T-waves.

2014.02.10 - 0000 - 01 - Smiles - Blog Case - EMS 12-Lead

Upwardly-concave T-waves are commonly taught as being associated with benign causes of ST-elevation, but that's only part of the story. For a more in-depth analysis, check out this quick review. While it's true that they are often seen with early repolarization, their presence here does not even remotely rule-out the possibility of STEMI when there are other signs pointing in that direction.

What are those other signs?

Chief among them is reciprocal ST-depression.

2014.02.10 - 0000 - 02 - Reciprocals - Blog Case - EMS 12-LeadIn this case reciprocal ST-depression is present in I, II, aVL, and V6 as highlighted above. While it's not unusual to see a T-wave inversion with a small amount of ST-depression in lead III with early-repolarization, ST-depression should not be present in as many leads as above were that the case. Additionally, this cannot be pericarditis because in that setting you are only allow ST-depression in leads aVR and V1. If you see ST-depression anywhere else on the EKG it is almost certainly not pericarditis.

At this point, by ruling-out early repolarization and pericarditis with one simple sign, we are almost certainly dealing with a STEMI. There's a lot more to this case though…

 

Getting a bit more advanced, there is a finding on this EKG known as "terminal QRS distortion."

Many folks will see ST-elevation like we see here in V2 and V3 and feel reassured because they've been told this shows "J-point notching." While it's true that a notched J-point is associated with early repolarization, that's not the cause of the downward deflection we see on the tail end up the QRS in this case. Instead, this is an abnormal S-wave and we should be worried!

2014.02.10 - 0000 - 03 - Normal vs Distortion vs Notching - Blog Case - EMS 12-Lead

On a normal ECG we should see a deep S-wave in V2 and at least a moderate-sized S-wave in V3, but on this EKG both S-waves are markedly diminished in size and in-fact don't even dip below the baseline. This is classic "terminal QRS distortion." The final portion of the QRS has been quite literally pulled upwards by the ST-segment elevation, and when you see this pattern you should be thinking about anterior STEMI.

 

Finally, let's get onto our last advanced topic for this EKG, and that is the ST-elevation in aVR. Well, that's actually a rather common topic that has been vastly over-simplified in the past, but we're going to do it right and go over what that elevation really means here.

In the most basic sense it means the ST-segment vector, also known as the "injury vector," is directed to the right.

Most readers have probably never been introduced to the concept of ST-segment vectors and that's alright. In an attempt to keep you ahead of the pack I'm going to be slowly introducing and then diving into this topic over the coming months. If you have no idea what I am talking about don't worry because that's the way it's supposed to be. My goal at this point is just to introduce you to just how I use this knowledge in my interpretations and hopefully show you why it's worth learning down the line.

And, while the handful of people who are familiar with this stuff roll their eyes, let me describe in detail what the injury vector is telling me:

On this EKG the ST-vector is almost exactly 180 degrees in the frontal plane and is roughly directed towards V1 in the transverse plane. This is consistent with LAD occlusion, but where in the LAD? A typical proximal LAD occlusion would have a more cephalad frontal plane vector from 210-250 degrees, while a classic mid-LAD occlusion would be isoelectric in the frontal plane with no limb-lead changes. So this could be an unusual mid-LAD occlusion, but what kind of anatomy could produce such an extra rightward "kick." Assuming this is not a proximal LAD occlusion we also assume the lesion is distal to the first diagonal branch, but that raises an issue. Typically the takeoff of the first septal-perforator is proximal to the first-diagonal, so a mid-LAD occlusion is distal to both (which is one reason why we typically see minimal limb-lead changes in that case). There is a not-uncommon variant of anatomy, however, where the first septal perforator arises distal to the first diagonal. That's it! This patient likely has a mid-LAD occlusion proximal to the first septal branch but distal to the first diagonal artery.

Most readers who suggested a lesion location when this EKG was first posted claimed it would be a proximal LAD because of the elevation in aVR, but the above line of thought suggests differently. Not only is it informed by the elevation in aVR, it also takes into account the more-caudal-than-expected injury vector that doesn't quite fit with a proximal LAD occlsion. So what happened?

The patient was taken to cath where his mid-LAD occlusion was identified and stented.

Unfortunately we do not have information regarding the anatomy of the septal and diagonal arteries, but I believe the thoughts listed above to be a not-too-unreasonable suggestion for just why we could be seeing aVR elevation in the setting of a mid-LAD lesion. I've even got a reference, though the text is in Serbian which I cannot read… The image, however, speaks for itself.

2014.02.10 - 0000 - 04 - Anatomy - Blog Case - EMS 12-Lead

Again, I'd like to thank Dr. Bojana Uzelac for submitting this case along with her suggestion for the possible coronary anatomy involved; I'm definitely in agreement! I hope everyone from beginners to more advanced readers were able to take something from the discussion. Let me know in the comments and I would love to dissect this case further!

2 Comments

  • Jos says:

    Just curious why you don't mention the q waves in V2-V3. Are they not significant enough? Also, the T waves in V2-V5 look nearly symmetrical, pointing to ischemia and/or infarct?

    Thanks.

  • Good eye Jos! I mostly glossed over the q-waves in V2-V4 to try and keep my verbosity under control. Despite their small size, in this setting they are definitely significant and do indeed contribute to the diagnosis.

    While you are also correct about the T-wave morphology being symmetrical, I skipped that one because I personally don't get much use out of it. My issue is that I've seen way too many cases of normal T-waves that are just as symmetrical as above, so while it's another piece of the puzzle pointing towards STEMI, in my mind it's just a tiny nudge. If I had to assign these T-waves a likelihood ratio it would be something low, like a LR+ of 1.4 or so.

    That said, I think another nice teaching point to be found here is that while the anterior T-waves are symmetrical, the ST-elevation in those leads skews your perception and makes them look asymmetrical and off-balance. Only by covering up the QRS and ST-segment with your hand do you really get the sense that the upstroke of the T-wave is really very similar to the downstroke.

    In fact, that trick for seeing symmetry better could make a nice post someday if I can get around to it…

    Thanks for reading and commenting!

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EMS 12-Lead

Cardiac Rhythm Analysis, 12-Lead ECG Interpretation, Resuscitation
Comments
Christopher Watford
59 year old male: chest pressure – Conclusion
Tony, From the initial ECG it appears that the pattern of ST-elevation is suggestive of a proximal RCA occlusion. However, at cath it was instead found to be an LCx lesion. Good question!
2014-09-18 13:20:09
Tony
59 year old male: chest pressure – Conclusion
Please explain why you suggest that the inferoposterior is caused by RCA but the Left Cx has been stented. Thank you.
2014-09-18 06:17:03
Keren Levi
The 360 Degree Heart – Part I
Lately, a few paramedic-students arrived at my station. So i tried to explain that basics at my best simpliest way. After readinv your perfectly coherent "article", i couldnt stop smily for knowing we both thought of same phrases and associatives words. For me it is a great compliment! Thanks for writing! Cant wait for part…
2014-09-17 19:34:44
Richard Kenkel
64 y.o. Female with CP – “And then I gave her a NTG…”
Cardiac arrest? Its a RELATIVE contraindication. You need to use clinical gestalt. Her blood pressure is quite high, and her heart rate is average, she would probably tolerate nitro quite well. Provided she's not on beta blockers or calcium channel blocker, orthostatic hypotension etc, from what I can tell she'd compensate just fine. While there…
2014-09-16 02:05:12
Stephen Smith, of Dr. Smith's ECG Blog
59 year old male: chest pressure
Inferolateral MI, not RV (T-wave down in V1)
2014-09-14 18:16:53
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