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Wednesday, August 15, 2012

Importance of the Prehospital ECG

I've talked about the evidence for liberal and frequent ECGs in the field. This, however, is not a literature review, but a "real-world" example.

A patient was brought into the ED recently, treated by Milford Fire. Fortunately for the patient, paramedic Eric Mohr was on duty, and did some nice ALS work.

EMS Course
 An elderly female had developed chest pain, abruptly, while asleep. It wasn't a mystery - she described "squeezing" pain that radiated to the jaw. The first ECG, from onscene, was not exactly a stumper either:

Like I said, not subtle.

Transport was intiated, aspirin was given. They were just about to patch in and call for a cath-lab activation, but decoded to grab one more ECG as evidence. (Note the change in time - they switched to an LP-12 that hadn't been adjusted for daylight savings.)

Huh, no more STEMI. Or anything, really.

Furthermore, the patients pain was starting to resolve as well. Aside from brief period of sinus bradycardia that resolved with atropine, the patient's symptoms continued to improve.

In the ED
By the time they reached the ED, she was almost symptom-free. Our ECG was consistent with that of EMS - very, very normal.

More normal than mine. Seriously.

Tell me if you see anything there - I didn't.

Since the patient was now utterly symptom-free, with a normal ECG, I put her in a bed near the desk, and checked in every 10 or so minutes to see if she was feeling anything changes.

About an hour later, she reported the same feeling in her chest and jaw, and I grabbed another series of ECGs:


Hmmm. I wasn't sure if the one little change I was seeing was real, so we grabbed V4R (PDF download there). I don't have the actual ECG of that lead (by then there was practically a sheaf of tracings, and it got lost in the pile), but it stuck in my memory. Let me draw it for you:
V4R - According to the courtroom artist
As I described it to the cardiologist, "It's only about 0.25 mm, but that ST segment just wants to come up!"

This ridiculous interpretation of mine made sense to cardiology, and the cath lab was activated, despite the absence of classic STEMI criteria, and a patient whose symptoms had again resolved.

"Classic" STEMI criteria, from Rokos 2010.

Good thing too. She ended up having a 99% occlusion of the RCA.

From this episode, I think there are 2 lessons to take away.

EMS needs to grab ECGs early and often.
If Eric hadn't obtained that initial ECG, this would have been a far more difficult case. It was pretty clear from the onset that she had troubles with her inferior wall. This would have been very difficult to demonstrate solely on the subsequent ECGs, however.

Look at aVL
For this, I give all the credit to Stephan Smith. One of his frequent teaching points is that ST depressions or T-wave inversion in aVL is often the herald, the very first ECG indication of an impending inferior wall STEMI.

He has made this point recently, as well as on numerous prior occasions. Go read those, and look at the tracings, and see how the cases unfolded with EMS and in the ED. Pay special attention to how the emergency physician and cardiology approached the situation. These aren't straightforward cases, and goes beyond "STEMI 101."

The Bottom Line
Yes, it's true that you expect to see reciprocal changes in aVL and perhaps lead I, with an inferior wall MI.

But in a patient with ischemic-type symptoms, and no ECG changes expect for this pattern in aVL, keep your eyes open for ECG evolutions. Run a couple more strips. Grab some right-sided leads. Tell med control to meet you at the door to discuss the situation.

See you at 4 AM!


  1. We've been operating under the principle that only 1 prehospital ECG which meets criteria is required for activation, even if subsequent 12-Leads do not.

    I'm reminded of the case Dr. Smith posted of a patient whose symptoms had abated along with their ECG changes resulting in a deactivation of the cath lab, only to code later.

    1. I'm not sure that all cardiologists feel that way, however. Many of the interventionists I work with prefer a classic situation (chest pain & ongoing STE) before hauling in the team. The culture is clearly different at your institutions, but I am doubtful that evidence exists to definitively settle the issue.

      I was looking a completely symptom-free patient, with an ECG that didn't even hint at an ongoing ischemic issue (e.g. no wellenoid pattern, no hyperacute T-waves, no ST depressions). That's a hard sell in many places, even for Stephan Smith!

    2. Rereading, I was a bit too specific when I meant to speak in the general sense. I think for the completely symptom-free patient (i.e. not on a 100 mcg/min NTG drip) without ECG changes you have to consider spontaneous reperfusion and change your treatment plan accordingly.

    3. This is one of the reasons I tend to lean fairly strongly away from Tx with opiates for CP unless the patient is clearly heading to cath. I've seen a couple of patients with definite unstable angina, if not stuttering lesions, who got placed on the back burner to simmer in tele for a couple of days after the narcs settled down their pain and the treating physicians became less concerned.

      I hate feeling that way because there's almost no studies on the topic and the argument sounds very similar to the one folks used to make for withholding analgesia in abdominal pain, but for here it seems to make slightly more sense. In fact, I just had a good friend of mine who is a nurse undergo a quad bypass following just such a scenario. If our ED director hadn't visited her upstairs on day 2, noticed that she looked-like-shit, and made a big stink over her condition, she probably would have spent a couple more days just chillaxing with UA and the morbidity and mortality that brings.