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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.

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.

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.

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).


(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.)

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