Scouring the web for cheap textbooks, I happened upon something of which I wasn’t even remotely aware: alternate ECG lead placements. As has been highlighted in previous posts by myself and others, cardiac scientists have strict guidelines that ensure we perform an ECG procedure to an accurate and repeatable standard, so it came as a bit of a surprise to discover that there existed a different way of carrying out the test with an aim to view specific activity.
The Lewis lead, named after Sir Thomas Lewis, is an alternate placement that can be used to better view atrial activity in relation to that of the ventricles. In many ECGs, it can be rather difficult to assess P waves; whilst they are represented using standard lead configuration, they are much less apparent than ventricular activity, due to the nature of the ECG’s detection mechanisms.
Using the Lewis lead configuration, it is possible to increase the detection of atrial activity and diminish that of the ventricles and gain a clearer picture of atrial fibrillation, flutter and, in the case of the article that brought my attention to this system, improving P wave recognition in wide QRS complex tachycardia.
The configuration is as follows:
- RA electrode on the manubrium
- LA electrode on the 5th IC space, right sternal border
- LL on the right lower coastal margin
- RL remains in the standard SCST position
- Adjust calibration to 20mm/mV
As shown on the diagram, a three lead configuration is still present, as in Einthoven’s triangle, but Lead I now travels directly over atrial activity. For this reason, Lead I is used as the monitor lead and the one from which a rhythm strip should be taken.
On the trace itself, there is a marked visual difference. The following were recorder on the same patient and we begin with the standard electrode configuration:
And now introducing the Lewis lead setup:
The P waves present in these altered leads are much more pronounced.
There are more lead systems that are used in the diagnosis a variety of different conditions such as Brugada syndrome. I’ll research and cover these and try to get some more traces using the Lewis lead system throughout the year.
Traces courtesy of ekgcasestudies.com
The Student Physiologist 
Awesome man looking forward to hearing more about the Lewis lead system and how it can be used. Is it used in practice today?
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From what I’ve seen, the Lewis lead, as well as other altered lead systems aren’t commonly used clinically, but in specific cases they are a recognised tool that have shown benefit.
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