STEMI Interpretation

I’ve been spending a great deal of time at my clinical coordinator job looking at STEMI cases, as well as putting together educational material.

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’m been sort of lucky lately in that I’ve had some idiot-proof STEMIs. Take this one for instance:

Or this one:

In what is becomming one of my favorite expressions regarding STEMIs. “Not Subtle.”

Unfortunately, many of the real world 12-leads can be classified as very subtle. I’ve seen 12-leads that I wouldn’t call STEMIs that turned out to be, and some I would call STEMIs that turned out to have negative cardiac enzeyemes and clear arties.

The other day I came across a new study just published in the American Journal of Cardiology. Differentiating ST elevation myocardial infarction and nonischemic causes of ST elevation by analyzing the presenting electrocardiogram in the February 2009 issue.

Here’s what it was about. They recruited 15 experienced cardiologists from across the world and gave them each 116 ECGs that had ST elevation of some sort or another whether it was a true STEMI or imposters like LVH or early repolarization and asked them, assuming the generaic patient had chest pain, to decide whether or not they should be sent to the cath lab or not based on the ECG. And if they were not going to send them to the cath lab, they had to check one of 8 reasons why not.

Of the 116 only 8 were STEMIs based on the patient’s final charts. The rest were nonishemic ST elevations.

The cardiologists recommended from 7.8% to 33% of the patients go to the cath lab with an average of 19% being sent. And when it came to assigning reasons the researchers found a wide varience in the cardiologists’ interpreations of the same ECGs.

The study includes 5 sample ECGs where the reader can make their pick and then read how the cardiologists saw it.

Only 5 of 15 called this one correctly. (Answer to follow)

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.

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.


  • Mikey says:

    So what was the diagnosis of the last 12-lead?

  • brendan says:

    Feldman JA, Brinsfield K, Bernard S, et al: “Real-time paramedic compared with blinded physician identification of ST-segment elevation myocardial infarction: Results of an observational study. American Journal of Emergency Medicine. 23[4]:443-448, 2005

  • Tom B says:

    I’m going to guess ventricular aneurysm. That’s a tough one! Dr. Smith wrote an article on the topic.T/QRS ratio best distinguishes ventricular aneurysm from anterior myocardial infarction. Am J Emerg Med 2005 May;23(3):279-8I replied at the PH12ECG blog.Interesting post! Thanks, Peter.Word verification: mesested

  • Tom B says:

    brendan – The study you quote proves that paramedics can be trained to identify STEMI with a high degree of accuracy.Just like studies performed in Seattle shows that paramedics can be trained to be proficient with advanced airway procedures.What we need to do is look at what King County Medic One and Boston EMS are doing and “mimic” them! :)Word verification: arspl

  • TOTWTYTR says:

    The diagnosis of MI, whether STEMI or NSTEMI, is a combination of ECG, History, and Physical exam. Thus said Marriott years ago and thus it still is and thus it will most likely ever be. The monitor is a tool, just like every other piece of medical equipment we have. It’s no more or less subject to misuse than is that spawn of the devil, the pulse oximeter. The secret of Boston, King County, and other systems that are successful in having their medics do “advanced skills” is a low medic to patient ration, continuing education, involved medical directors, and pay and benefits that tend to retain experienced medics. Anyone can do, it’s just that most systems are more worried about cost than the are value received for money spent.

  • brendan says:

    Just like studies performed in Seattle shows that paramedics can be trained to be proficient with advanced airway procedures.Boston has one of those too. ;-)The secret of Boston, King County, and other systems that are successful in having their medics do “advanced skills” is a low medic to patient ration, continuing education, involved medical directors, and pay and benefits that tend to retain experienced medics.Exactly. The one thing you forgot though is that their initial education (both in-house, coincidentally) is light years beyond what most patch factory medics get before receiving their license to kill.

  • Tom B says:

    You’re right! Boston does have one of those, too. Your point is also well taken with regard to initial education.That’s why it’s dangerous to apply the specific case to the general case when the data is coming from the top 1% of EMS systems in the country.Who else bothers to collect high quality data?As I’ve said in the past, just because a squad of Navy SEALs can sneak behind enemy lines and blow up a bridge doesn’t mean that a squad of recruits from Ft. Jackson could reasonably be expected to accomplish the same task.Everyone needs to measure their own data. But that not only requires work; it also requires change.It’s much easier to attack the credibility of authors who publish studies showing paramedics may not be the gods of airway management after all.Or, suggest that the studies are flawed because they don’t take into account injury severity.Wouldn’t it better to publish your own data, so you can say, “Our paramedics are doing well and so are our patients and here’s the proof”? Word verification: spous

  • PC says:

    Thanks for the comments and discussion. The point of my post was that no matter how good people may be at interpreting based on a 12-lead, the 12-lead alone, even when read by an expert is no clear indication. Many of the 12-leads we get in real life are like these — in the gray area — not the huge ST elevations we are taught in classes. All we can do is our best. These are no perfect interpreters, no matter what your’s the outcome on the ECG from the study: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 stenosis40%, proximal left anterior descending artery stenosis 95%, left circumflex artery 60%. The patient underwent PPCI of his proximal left anterior descendingartery. STEMI was diagnosed by 5/15 readers (33%).”

  • Tom B says:

    Sorry about that! I had a little glitch.Thanks for the follow-up, Peter.It’s exactly the terminal T-wave inversion that makes this injury pattern look “old”.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.

  • Steve Whitehead says:

    Great post Peter. I’d add that it seems like physicians are much more comfortable with the ambiguity of 12 interpretation than we medics seem to be.I think we expect to nail it on the head every time and we feel like we did something wrong when we call the MI and we’re wrong, or we fail to alert when the patient is infarcting. We’re not very forgiving of ourselves on this point or many others.I’d guess that the cardiologists weren’t terribly surprised by these results.

  • alan says:

    looks like a wicked STMI to me!

  • Anonymous says:

    A great post,
    Paramedics are eager to learn and generally aggresive in finding and treating STEMI's. If you happen to work in one of the few systems with a paramedic contact time to PCTA of less than 90 min, 90 percent of the time you see a great survival rate and MD's and Paramedics working hand and hand. Providing what the patient needs, a trip to the cath lab and no dawdling in the ED.
    It all boils down to a great medical director, who is proactive in his system, a good training department, and Qi and most importantly EMT's and Paramedics who love what they do.
    An interesting thing i found written by Dr Garvey in charlotte NC
    Once again GREAT POST, can we expect more?
    The old Paramedic you young guys wish would retire and free up the seniority.