Lead misplacement is a common issue encountered when obtaining and interpreting EKG's that can lead to diagnostic and therapeutic errors. It is important to first understand regular lead placement to understand misplacement.

There are 6 limb leads and 6 chest ('precordial') leads. The precordial leads are placed on the chest and closest to the heart, producing the greatest amplitudes. The 6 limb leads are actually produced from 3 leads placed on the patient. The unipolar (one vector/direction) leads are aVF, aVL, and aVR. The bipolar (vector from difference between leads) leads are also produced from the 3 leads placed on the limbs.

Misplaced V1/V2

V1 or V2 are commonly misplaced and are usually placed too high on the chest. There are 3 main clues to this, with the biggest one being that the P wave morphologies are more negative than expected. Normally, the P wave is biphasic in V1 and are upright in V2. If the P wave in V2 is biphasic or inverted (and V3 is normal), one should suspect lead misplacement. Additionally, upwards displacement of these leads produces an incomplete RBBB pattern. Note that this is a false incomplete RBBB as one does not see the changes otherwise throughout the precordial leads. This can produce concern for possible PE and, sometimes, even Brugada syndrome falsely. Lastly, lead misplacement of V1/V2 can make these leads look similar to aVR, usually producing septal Q waves as opposed to the incomplete RBBB pattern.

Limb Lead Misplacement

Limb lead misplacement can comprise misplacement of any of the limb leads and this is typically reversal. The most common one is left and arm reversal. It is very important to understand Einthoven's triangle to understand the changes on an EKG. Common clues to this are unusual axis, unusual directionality to aVR, aVR and V6 going in the same direction, and unusual P wave morphology in lead II.

LA/RA Reversal

This is the most common limb lead misplacement as the one obtaining an EKG mixes up left and right. The first thing that is noticeable is that aVR and aVL are reversed (making aVR positive). Leads II and III are also reversed, though that is far less noticeable. Lead I becomes inverted and is only partially similar to aVL, which can be remarkable as well.

LA/LL Reversal

This would be the next most common limb reversal, though is quite rare. The 2 groups of reversed leads are I and II, as well as aVF and aVL. Lead III is then inverted. The best clue to this is that the inferior leads are not all in the same direction.

RA/LL Reversal

This is the rarest of the reversals for obvious reasons. The reversed leads are aVR and AVF, as well as I and III. Lead II is inverted. Once again, lead aVR is positive, which is the biggest clue to a potential lead misplacement or reversal. Additionally, the P wave in lead II is inverted.

Examples

Further Reading:

https://litfl.com/misplacement-of-v1-and-v2/

https://litfl.com/ecg-limb-lead-reversal-ecg-library/

http://hqmeded-ecg.blogspot.com/search/label/lead%20misplacement