Top 10 myths about prehospital 12 lead ECGs

A recent thread at JEMS Connect has reminded me how many myths are circulating about prehospital 12 lead ECGs.

1.) If you’re close to the hospital, performing a prehospital 12-lead ECG is a waste of precious time.

The prehospital 12-lead ECG is an important triage tool. The closest hospital is not necessarily the closest appropriate hospital! In addition, just because you’re close to a PCI hospital doesn’t mean you can’t save 15 minutes of ischemic time by giving the hospital early notification that you’ve identified a STEMI patient.

2.) Prehospital 12-lead ECG monitors are incapable of capturing diagnostic quality 12 leads.

As long as the low frequency (high pass) filter is set to 0.05 Hz (which happens automatically when you capture a prehospital 12-lead ECG) then you will record accurate ST segments. A more important issue is data quality and lead placement, which is a training issue (and a credibility issue).

3.) It’s important for the ED staff to perform another 12 lead ECG to confirm that it’s really a STEMI.

I don’t care if the ED staff performs another 12 lead ECG as long as the cath lab has already been activated based on the prehospital 12-lead ECG and they are already taking advantage of parallel processing (for those patients who show obvious STEMI in the field). However, there’s nothing “magic” or “special” about the ED’s 12 lead ECG. Serial ECGs can be extremely important, but mostly for suspected ACS patients with nondiagnostic (or borderline) ECGs on initial presentation. If they’re waiting for their own 12 lead ECG before activating the cath lab, then they’re wasting valuable time.

4.) If ST segment elevation resolves by the patient’s arrival at the hospital, then it’s not a STEMI, and the patient doesn’t need an emergent cath.

Should you wait for the cardiac biomarkers to come back positive before sending the patient to the cath lab? I’m not sure that’s a good idea. The case I posted last month shows that even when ST segment elevation resolves by arrival at the hospital, the patient can still have an occlusive thrombus in an epicardial coronary artery.

5.) Nitroglycerin is contraindicated for patients with suspected right ventricular infarction.

Not all patients with inferior STEMI have RV involvement, and not all patients with RV involvement develop the hypotensive syndrome. Consider the vital signs, the heart rhythm, and the physical exam, and treat accordingly. Sometimes the patient just needs a preemptive fluid bolus. The new 2010 AHA ECC Guidelines say to use NTG “with extreme caution, if at all” in the setting of suspected right ventricular infarction. It’s not quite “contraindicated” but that’s a strong statement! What do I say? “Use your brain!”  There’s no substitute for sound clinical judgment!

6.) Prehospital 12-lead ECGs are important tools to help distinguish between VT and SVT with aberrancy.*

If you’re using QRS morphology to “rule in” VT, then be my guest! If you’re using it to justify giving a CCB to a patient with a wide complex tachycardia, then I think you’re crazy. That’s not to say that I don’t capture 12 lead ECGs for all patients who present with cardiac arrhythmias, because I do. Documenting the arrhythmia is very important. Sometimes it even helps with the diagnosis. But I do not base my treatment decisions on QRS morphology and neither should you.

7.) If the hospital ignores the prehospital 12-lead ECG then there’s no point in performing one.

I’m sympathetic to this view, but it’s a defeatist attitude. You should capture a prehospital 12-lead ECG with the first set of vital signs, prior to oxygen and nitroglycerin. That way, when you “clean up” the 12 lead ECG prior to arrival, you can hand them a picture of what the patient looked like prior to your intervention. It’s hard to imagine that a board certified EM physician would ignore that. In any case, the ECG should be made a part of the patient’s record, because the cardiologist may care.

8.) It’s easy to identify STEMI on the prehospital 12-lead ECG.*

Technically this isn’t a myth. It is easy to identify a home run STEMI on the prehospital 12-lead ECG. However, that should not be interpreted to mean that reading a 12 lead ECG is easy, or that just because you’ve been taught to identify an obvious STEMI with reciprocal changes that you can read an ECG as good as a physician. You might be able to, but you probably can’t. Identifying ST segment elevation on the 12 lead ECG is easy! Differentiating between true STEMI and the STE-mimics can be difficult. Sometimes very difficult.

9.) It’s impossible to identify STEMI in the presence of LBBB.

Sure you can. You can use a modified form of Sgarbossa’s criteria and you can perform serial ECGs. A moving ST segment suggests dynamic supply vs. demand characteristics consistent with ACS. Is it difficult? It’s more difficult. Impossible? Hardly.

10.) Axis determination is “nice to know” information but you don’t really “need to know” it.

That’s like saying “paramedics don’t really need to know how to read a 12 lead ECG.” That’s fine, if that’s really your opinion. Just don’t complain when you’re asked to transmit the ECG for physician interpretation.


  • Mark says:

    Quick question about #7…sort of. Some medics say do the 12-lead before any interventions. Others say do the interventions while you are getting a 12-lead when you have chest pain. (O2, ASA, NTG) Is there any published evidence that O2 and NTG can cause signs of a STEMI on a 12-lead to disappear? If it’s really a STEMI with full, transmural involvement, I can’t imagine that a nasal cannula and a shot of NTG is going to change the 12-lead significantly. (Or am I totally wrong here?)

  • Tom B says:

    Mark -I’ve seen this happen on several occasions. See the case study from March that shows regression of ST segment elevation (link in #4).As for published evidence, I’m not sure whether or not there’s anything in the peer reviewed literature. If not, there may be something on the way from Hennepin County EMS.I’ll look into this and let you know what I find out. Thanks for the comment!Tom

  • lisa plebani says:

    A few things….yes the closest hospital may not always b the best, u r correct, (ie..Aria Bucks doesn’t do caths in house they get shipped to Torresdale) but if ur going to bypass the closest facility with an unstable pt because u feel a different hospital would b in their best interest, u must contact medical command to do so, that’s not a decision we can make, u must have medical command authorization to do so. Also, unfortunately (at least for the hospitals in Bucks County), when the als providers do call a stemi, the cath lab is not activated until that is verified by the ed physician, maybe this will chAnge in the future, or when ekg’s r transmitted, but as of right now, I agree that time can get wasted due to waiting to activatE the cath lab, however in their defense there has been numerous times when stemis r called by providers, when indeed there is no stmi at all, which is maybe why the hospitals do this. Just because the monitor says there’s a stemi, it doesn’t necessarily mean there is, which is why providers need to b competent in reading 12 leads. And to answer someone else’s question, yes, every intervention we do can absolutely have an impact on the 12 lead, which is why a 12 lead should b performed with the initial vital signs, besides a pt should remain still while a 12 lead is performed, kinda hard for them to remain still sometimes while doing an Iv, or while the truck is in motion, which will also cause artifact. U can Always repeat a 12 lead, but an initial one should b performed with the initial vital signs.

  • Medic2011 says:

    Okay, I'm new to this level of treatment, but I'm observant of what takes place in the hospital as I have been performing 12 leads as a part of my hospital clinical rotations.  I was fortunate enough to have a remarkable cardiology instructor.  The most important thing I've noticed is that a high majority of techs and nurses that perform 12 leads in the hospital have no idea how important lead placement is and why they are placed where they are.
    I recently went to perform a second 12 lead at the request of the ER doctor.  The ECG had just been done by an RN.  I explained to the pt. that I needed to do another ECG, so when she exposed her chest to allow me to hook up the leads, it became very apparent why I was doing this a second time.  Leads V3-V6 were lined up neatly across the anterior chest wall and literally resting against each other.  Lead V2 was placed smack dab on top of the sternum and V1 was actually close enough that I didn't have to move it.
    Another time, I walked into a treatment room where an RN was hooking up a pt. to the 12 lead.  I could see immediately that she didn't know what she was doing as she had the leg leads on the forearms!  I told her I would be happy to finish it while she did something more important.  I proceeded to move the legs leads to the proper locations and she made the statement "oh yeah, I forgot they don't want us to put them there anymore!"
    My point is that a prehospital 12 lead may be the best 12  lead a doctor sees on this pt.  If a paramedic can do one without sacrificing treatment time, I'm all for it.

  • Nathan Stanaway says:

    Two things,  Medic 2011 I think you should have corrected and educated the nurse or tech who made the errors with lead placement.  Its important.  These are people's lives we're dealing with and  pride be damned.
    Lisa going to the closest APPROPRIATE hospital is of utmost importance and is sometimes the only difference between being transported by ambulance and choosing where to go from the yellowpages.   You absolutly should go where the problem can be fixed, if you dont, whats the point?  To compare this to something I think is well accepted; You wouldnt take a major trauma to a band aid station when the trauma center is 15min further.   Would you?
    Tom great post Im forwarding this one to more than the normal folks I spam!

  • William Dillon says:

    Great post.  Prehospital ECGs are critical to improving outcomes in STEMI pts.

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