ECG Pointers – The Lewis Lead

Authors: Brannon Inman (EM Resident, San Antonio, TX) and Lloyd Tannenbaum (EM Attending Physician, San Antonio, TX) // Reviewed by: Jamie Santistevan, MD (@jamie_rae_EMdoc, EM Physician, Presbyterian Hospital, Albuquerque, NM); Manpreet Singh, MD (@MPrizzleER, Assistant Professor of Emergency Medicine / Department of Emergency Medicine – Harbor-UCLA Medical Center); and Brit Long, MD (@long_brit, EM Attending Physician, San Antonio, TX)

Welcome to this edition of ECG Pointers, an emDOCs series designed to give you high yield tips about ECGs to keep your interpretation skills sharp. For a deeper dive on ECGs, we will include links to other great ECG FOAMed!

The Case:

It’s a slow night in a single coverage ED and you think to yourself, maybe now is a good time to take a nap.  Then, suddenly, the phone rings.  It’s your charge nurse and there’s a new patient arriving and the chief complaint? Weakness… You walk into the room and see an 80 year old male with a history of CAD sitting calmly in the bed. Triage vital signs are unremarkable except for tachycardia at 143. As you start to ponder what could be causing this octogenarian’s weakness, your tech hands you this EKG1:

Figure 1: Wide complex tachycardia.

Well, that was unexpected.  Remember, with wide complex tachycardia it is important to rule out ventricular tachycardia. You call the patient’s cardiologist and explain what is going on. She asks if you see any AV dissociation, which is not easily appreciated. She asks you to perform a Lewis lead ECG to better evaluate the rhythm while she is charging her Tesla to drive in. You agree and hang up the phone, and think to yourself “A who-lead ECG?”.


The Lewis Lead ECG:

Originally described by Sir Thomas Lewis in his 1913 publication “Clinical Electrocardiography”, the Lewis lead ECG was originally adapted to better identify p waves in atrial fibrillation, or “auricular fibrillation” as it was called in that publication. In the original publication described a “convenient 5 lead placement” about the right atrium (Figure 2) to better detect atrial electrical activity. In this configuration, special attention is paid to leads I and II to look for atrial activity.2


When to use the Lewis Lead ECG:

Practically speaking the Lewis Lead ECG is used in one of two situations. In the setting of a wide complex tachycardia and when atrial fibrillation is in question. In both instances the clinician is evaluating evidence of AV disassociation. From a macroscopic vantage point, the Lewis Lead ECG is a practical tool to use when a physician wishes to evaluate for electrical activity from the sinoatrial node.


Lead Placement:

There are several options for lead placement outlined below. The common theme among them is that leads are move from the left and right arm to either the right side of the sternum or the sternum itself.

Figure 2: Original Lewis lead placement by Sir Thomas Lewis. From Lewis T. Auricular fibrillation. In: Clinical Electrocardiography. 5th ed. London, UK: Shaw and Sons; 1931, page 91

There are several other modified Lewis lead placements have been described since Dr. Lewis’s original paper. In 2009, a case report was published utilizing Lewis lead ECG placement to detect A-V dissociation in a wide complex tachycardia. In this case report the right arm electrode was placed in the right second intercostal space and the left arm lead was placed in the right fourth intercostal space (Figure 3).3

Figure 3: modified Lewis lead placement From: The Lewis Lead : Making Recognition of P Waves Easy During Wide QRS Koomen E et al, 2009.

In 2016, 47 patients undergoing an electrophysiology (EP) study were enrolled in a study to validate the above placement of the left and right arm leads for a Lewis Lead ECG. During EP stimulation, standard ECG and Lewis lead ECGs were obtained. In this study, leads were configured, as described above, with the right arm electrode was placed in the right second intercostal space and the left arm lead was placed in the right fourth intercostal space (Figure 4). In this study, the Lewis lead placement was associated with increased AV conduction detection.4

Figure 4: modified Lewis lead placement From: The Lewis Lead for Detection of Ventriculoatrial Conduction Type Huemer et al, Clinical Cardiology (2016) 39(2) 126-131

Finally, Life in the Fast Lane describes another Lewis lead placement type. The notable difference being that the right arm lead is placed over the manubrium rather than the right second intercostal space (Figure 5).5

Figure 5: modified Lewis lead placement From: Lewis lead, LITFL,  Medical Eponym Library. Cadogan M

There are several options for placement of the leads to obtain a Lewis Lead ECG, all with a similar theme of clustering leads about the right atrium to better detect electrically activity. Typically, scour lead I in a Lewis Lead ECG for atrial activity, assuming one is not using the originally described method. This type of lead placement has the potential to better detect a-v association and is most frequently used for identifying wide complex dysrhythmias and atrial fibrillation.4,5

Back to the case

With this new knowledge in hand you obtain this Lewis lead ECG.

Figure 6: Lead II atrial electrical activity Lewis Lead ECG.

There are identifiable p waves associated with each QRS complex (Figure 6). Likely this is not VTach. Given the heart rate this is likely 2:1 aflutter with aberrancy or an SVT with aberrancy.


Key Points:

  • The Lewis Lead ECG is a practical and useful tool to look for evidence of AV disassociation in ECGs. In the Emergency Department, it is most useful to look for p wave association in wide complex tachycardias to differentiate ventricular tachycardia from SVTs with aberrancy.
  • To perform this ECG simply move the right arm lead to the right 2nd intercostal space and the left arm lead to the right 4th or 5th intercostal costal space.
  • Once you have your chosen lead configuration, look through all leads for evidence of p waves. You’ll likely have your best luck in leads I and II.
  • If you don’t see AV association, you have to assume it’s not there (e.g., ventricular tachycardia).



  1.         Ventricular Tachycardia – Monomorphic VT • LITFL • ECG Library. Accessed February 28, 2021.
  2.         Clinical electrocardiography : Lewis, Thomas, Sir, 1881-1945 : Free Download, Borrow, and Streaming : Internet Archive. Accessed February 17, 2021.
  3.         Koomen EM, Braam RL, Wellens HJJ, et al. The Lewis Lead : Making Recognition of P Waves Easy During Wide QRS. Published online 2009. doi:10.1161/CIRCULATIONAHA.109.852053
  4.         Huemer M, Meloh H, Attanasio P, et al. The Lewis Lead for Detection of Ventriculoatrial Conduction Type. Clinical Cardiology. 2016;39(2):126-131. doi:10.1002/clc.22505
  5.         Cadogan M. Lewis lead • LITFL • Medical Eponym Library. Life In The Fast Lane, Nov 3, 2020. Accessed February 18, 2021.


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ECG Pointers – The Lewis Lead