The Bait and Switch – Error Leads To Delayed Reperfusion

The Case

Imagine you are an emergency physician working in a medium-sized community hospital.

It’s a busy day in the emergency department. You are the only physician on duty.

One of the nurses has called in sick, there is no tech, and the weakest unit secretary is on duty.

All the rooms are full, the waiting room is packed, the ambulance bay is jammed, and there are overflow patients waiting to be admitted.

There is a policy in the emergency department that the emergency physician shall review the 12-lead ECG of chest pain patients within 10 minutes of the patient’s arrival.

You are suturing a large laceration in a patient’s leg when a nurse walks in, holds up an ECG and says, “We have a walk-in chest pain patient in bed 4.”

lead placement error

It’s going to take you another 20 minutes to suture up the patient’s laceration.

What are your orders?


This patient was experiencing an acute inferior STEMI and reperfusion was delayed.

Those of you who predicted that the white and red electrodes were switched were exactly right. The frontal plane axis is in the right superior quadrant (no man’s land) which is unusual and should tip you off that there’s an error with lead placement.

What’s really unfortunate about this case is that physical inspection of the leads would have shown them to be placed properly. That’s because the leads themselves weren’t misplaced.

The leads were “plugged in” to the machine backwards.

The result was the transposition of the white and red electrodes.

In reality, you can still see the STEMI if you know what to look for. One of the “tricks” I teach students to help them identify acute posterior STEMI is to ignore the limb leads for acute inferior STEMIs and look only at the right precordial leads (V1-V3).

This helps “train the eye” to see subtle signs of acute posterior STEMI and this case demonstrates why having a “trained eye” could be potentially life-saving.

In this case, there is a slight downsloping of the ST-segment in lead V2.

Throw in the “classic” appearance of lead aVL (reciprocal change) and this 12-lead ECG is highly suspicious for acute inferio-posterior STEMI.

So, when trouble-shooting a 12-lead ECG remember to check both the leads and the connections!

Further Reading

The missed STEMI

Artifact in the limb leads: which electrode is responsible?

Updated 07/20/2016


  • phillip says:

    full set of obs pain score R side ecg, ? treat gtn if bp allows ?analgesia, monitor pt o2 via simple mask. iv access

  • yitz says:

    I would suggest right sided EKG, labs, seems that we might have here some ischemia to lateral & inferior leads.

  • Brandon O says:

    This is why ED overcrowding is a problem… overworked nurses rotate all the limb leads!

  • Mark P says:

    Depending on hospital protocol – , do another ECG in 5 mins, load aspirin, clopidogrel, call the cath team. ST ‘depression’ in V2 is an ST elevation equivalent for a posterior infarction. Interesting that the ST segments are ok in the inferior leads.: large Qs there, TWI. Wonder if this is an old inferior, with a new posterior; but sometimes the ST elevation can persist after an infarct and this may be a plain old NSTEMI. Quick chat to the patient might clear this up.

  • Mark P says:

    Good spot Brandon. Didn’t see aVR!

  • medic1008 says:

    hahahaha brandon !!!!

  • Mark P says:

    Right arm lead is on left leg; left leg is on right arm. So that makes lead I an ‘inverse lead III’; lead II an inverse lead II; lead III an inverse lead I. So the downsloping ST depression in lead I and lead II is actually ST elevation in the inferior leads. Makes this a true infero-posterior STEMI. Great case.

  • Brandon O says:

    Mark, I saw it as more of a clockwise rotation — right arm to left arm, left arm to leg, leg to right arm. But I see that swapping right arm and leg also works, and is simpler (therefore more plausible). I like it your way; nice catch. But I’d like a cleaner ECG to call depression… although since in your model aVL is still “legit,” I believe those inverted T-waves would count as reciprocal changes!

    Very neat, very enjoyable case.

  • “put him in a wheelchair and wheel him into this room. and for god’s sake, would someone teach the unit secretary where to put those damn leads?”

  • Christopher says:

    ASA, Oxygen by cannula as need for diff breathing. Repeat EKG now (with the leads on right) and in 5 minutes, Dual IV’s with a bolus, get the closest STEMI ER physician on the phone, and call 911 for the STEMI transfer. Inferior, Posterior MI with First Degree Heart Block.

  • Mark P says:

    @Brandon – I thought it was rotation as well, but then the limb leads didn’t ‘calculate’ properly. The only combination that worked was a swap between right arm and left leg.

  • Terry says:

    I agree with burned out medic. I would also give the pt the tv remote and a cup of coffee looks like it’s gonna be a while!

  • buzdad says:

    The P Wave is upside down, that is the main clue about lead reversal.

  • david says:

    Paddles have been placed in a wrong way. Check the leads and repeat. 

  • reversed limb leads, see avR , to do another correct ECG

  • abhi says:

    ask nurse to recheck alll limb lead , and  to re take one more ecg

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