ECG mimics of acute STEMI

Peter Canning over at Street Watch: Notes of a Paramedic has a recent post entitled STEMI Interpretation that’s worth checking out.

In it, he observes:

When we take a class in STEMI recognition, the ECGs, once you know how to read them, are all pretty clear cut. You can flash the 12-leads on the screen and a well-taught class will call out in unision “Inferior, Anterior, Anterior, Inferior, Lateral,” etc. You get tricky and you throw in the ST imposters, but they catch on. “Left Bundle, Right Bundle, LVH, Inferior, Anterior, Left Bundle,” etc.

The problem is when you get back on the street not all 12-leads are so cut and dried…

I couldn’t have said it better myself.

Unfortunately, a lot of paramedics feel so good about themselves after taking a basic 12 lead ECG STEMI recognition class that they buy into the mindset that paramedics can interpret an ECG as good as a physician.

In 99% of cases, it simply isn’t true. Not because paramedics can’t be taught to read an ECG as good as a physician, but because paramedics aren’t taught to read an ECG as good as a physician.

Peter goes on to discuss a recent article published in the American Journal of Cardiology that essentially shows that interpretation of ST segment elevation on the 12 lead ECG can be difficult, even for cardiologists.

This finding is not surprising. I have written about the problem of ST segment elevation in a previous post.

Peter goes on to quote the study’s bottom line:

This study’s findings reflect the diagnostic limitations encountered by cardiologists when the ECG is used as the sole diagnostic tool for STEMI. If experienced readers, using the current criteria and guidelines, cannot accurately and consistently distinguish between STEMI and NISTE, less-experienced readers cannot be expected to do so.

And then adds:

So take heart, paramedics, we aren’t expected to be seers. Just do the best you can to identify what you can. Cast a wide net when you do your 12-leads. Do serial 12-leads. One that is not obvious can soon grow into a not subtle one. Call the obvious ones, and bring attention to the possible ones. Evaluate based on patient presentation and ECG.

I am mostly in agreement, especially with regard to performing serial 12 lead ECGs. However, while we may not be expected to “be seers” in all situations, we can “be seers” in most situations.

With the proper training.

Tomas Garcia MD, author of 12 Lead ECG – The Art of Interpretation once told me the most common reason cardiologists fail their board exams is ECG interpretation.

ECG interpretation can be difficult. Admitting that is the first step to developing real expertise. It’s sort of the same as tracheal intubation in this regard. Just because you can intubate a patient with typical anatomy doesn’t mean you can handle a difficult airway.

Just because you can identify a homerun STEMI after an 8-hour introduction to 12 lead ECG class doesn’t mean you’re going to pick up on ventricular aneurysm.

There are always going to be false positive cardiac cath lab activations. If it never happens, you’re not being aggressive enough. If it happens too often, you’re being too aggressive.

A case like this from the Lost on the Floor blog could fool almost anyone, especially without an “old” ECG for comparison.

Can you be taught to identify the mimics of acute STEMI? Yes.

Can you be taught to identify acute STEMI in the presence of baseline abnormalities that mimic acute STEMI? Yes!

It’s difficult but it’s not impossible.

Peter had posted this ECG from the study and reported that only 5 out of 15 experienced ECG interpreters called it correctly.

In the comments he reports:

5 out of 15 experts correctly said this was a STEMI.

“A 57-year-old man with chest pain. There were QS waves in V1-V2. There was mild STE in V1-V2. There was terminal T-wave inversion V2-V6. There was T-wave inversion in I and aVL. Peak troponin I 26.84 ng/ml. Peak CKMB 29.6 ng/ml. Coronary angiography showed proximal left main stenosis 40%, proximal left anterior descending artery stenosis 95%, left circumflex artery 60%. The patient underwent PPCI of his proximal left anterior descending artery. STEMI was diagnosed by 5/15 readers (33%).”

I had guessed the ECG showed left ventricular aneurysm.

Consider this example from Brady WJ, ST Segment and T Wave Abnormalities Not Caused by Acute Coronary Syndromes. Emerg Med Clin N Am 24 (2006) 91-111.

As I noted in the comments, ventricular aneurysm is a difficult mimic because it’s not really a mimic at all. It’s an “old” MI with persistent ECG abnormalities.

It would be interesting to know if an acute thrombosis was found during intervention, of if this was one of those patients for whom chronic atherosclerosis finally became so occlusive that it caused cardiac injury.

My guess is that the ECG didn’t look a whole lot different after stenting.

Want to become an expert STEMI recognition?

See our video-based 12-lead ECG course at ECG Medical Training! 


  • Dave B says:

    i would think that it if it is an Mi, the the T wave inversions are “reperfusion” T waves, of the Wellens variety… perhaps with greater attention to serial ECG’s (which should be done anyway), a loss of the T wave inversion would be a great clue to reocclusion, and confirm MI… does that make any sense? lol

  • Ken Churning says:

    I would agree Tom. 

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