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Monday, May 7, 2012

The most difficult step in obtaining an ECG.

Quick post today, concerning a very common error I see both in EMS and ED patients - misplaced ECG leads. I would call this a pet peeve (as the techs and nurses I work with are well aware!), except that a peeve does not usually carry significant clinical implications.



An article in the curent issue of EMS World argues for the acquisition and transmission of prehospital ECGs by BLS crews. No argument there - that is exactly what happens in the ED. A tech acquires the ECG and runs it to me. If your system allows for easy transmission of ECGs, and if paramedics are scarce, this would be a common-sense approach to take.

Unfortunately, an accompanying illustration distracts from the main message.

Source
In an unfortunate twist, there are two errors of lead placement here. These errors are both common and possibly clinically significant.

The problems.

First, I believe V1 and V2 are located too high on the chest.


These leads should be located in the forth intercostal space (ICS), which in males is often within a fingerbreadth of the horizontal nipple line.

Reference
Another clue to V1 & V2 misplacement is their location relative to lead V4. Given that V4 should be located in the fifth ICS, the large vertical distance between V2 and V4 in the illustration suggests misplacement of V1 and V2 as well.



A second apparent error is that V3 is shown slightly medial to V2.


 It should properly be placed halfway in between leads V2 and V4.



Why is this important?

Misplacement of ECG leads, and especially V1 and V2, are common. One study compared the accuracy of cardiac techs, compared with nurse, physicians, and even cardiologists. No one, except the techs, came out looking too good.

The ovals represent the range of misplacement for each lead, broken down by training level. Ref.
These errors are not trivial. "Pseudo-infarction" patterns can be generated from incorrect lead placement, leading to erroneous cardiac catheterization lab activation, cost, and diversion of resources. In the example below, simply moving the V1 and V2 leads from the 4th ICS, then to the 3rd, and then the 2nd, produced ECG changes which the computer interpreted as suggestive of ACS.


Reference
Another example - you can see how an rSR' pattern is falsely generated as V1 and V2 are moved from the 4th ICS (in B-1) to the 3rd ICS, and then 2nd ICS (in B-3).

Reference

(Interesting aside - placing the leads in a higher ICS is used to assess for an occult Brugada pattern, But this is sort of a specialized technique, and I leave it to the electrophysiologists.)

Source
The Bottom Line

A recent post from Captain Chair Confessions highlighted the importance of proper lead placement, not only with regard to accuracy, but also in assuring that EMS appears professional and competent. I second that, but I have to acknowledge that many paramedics likely learned the incorrect position from preceptors within the hospital. Heck, in one of the studies mentioned above, the cardiologists were the people least likely to properly position V1 and V2!

So, kudos to David Howerton and the other authors on making a good argument for ECG acquisition as a BLS skill! But strive to demonstrate proper lead placement - it makes a difference

6 comments:

  1. Another area of potential concern is the consistency between EMS lead placement and ED lead placement. Our ED 12-Lead's won't use EMS electrodes...so off come ours and on go theirs. Makes life possibly a bit harder for the ED docs to interpret if "changes" occurred between two ECGs.

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    1. That's true, but there are things you can look for. As one of the articles (By Ilg) points out, the p-wave should be upright in V2. If there has been a change in both the p-wave axis and in the ST/T region, I would chalk it up to lead placement.

      Stuff like T-wave inversions or hyper-acute T-waves, which I look for in EMS 12-leads, should be pretty immune to "lead migration," I would think.

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    2. You can "make" Q-waves with patient positioning and electrode changes. You can also introduce axis changes with limb electrode placement. But, as you referenced, some careful consideration of other ECG features can help you determine if it's happened.

      I agree though that the big ticket items--prefaced with, "what I would call 'big ticket'"--aren't going to change.

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  2. At a hospital I am very familiar with that won't be named, they have a very simple approach to that issue: they don't even look at the prehospital tracings. Problem solved :)

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    1. And as a result, their false-positive rate for pre-hospital activation is zero. One way to approach the issue!

      When you say "the hospital," is this generally a problem with the doctors? I would think that if you shove a piece of data into the hands of most ED docs, they are going to look at it.

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    2. It seems to be more of an issue with patient hand-off because there's no real policy in place for what to do with prehospital tracings. Report is entirely verbal and there's no protocol that states prehospital ECGs should be placed on the chart, so even when a medic leaves loose tracings with the nurse, they almost always end up in the trash. Sure, they get scanned into the prehospital PCR, but those only show up in the ED well after the patient has been admitted.

      To the credit of the docs, if a medic brings them a tracing or has a concern they will address it immediately, but that assumes the medic picks up on a finding that may be subtle or only notable on serial tracings.

      Looks like I might have found a new work project for the summer...

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