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.
Update: 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 interpetation.
* Technically not a myth but requires qualification.