The Lewis lead configuration (S5-lead placement) is used to better detect atrial activity in relation to that of the ventricles.

P waves (reflecting atrial activity) are usually much less apparent than ventricular activity. The Lewis lead can be of value in amplifying these waves, allowing:

  • visualisation of flutter waves in atrial flutter;
  • clarifying the mechanism of an atrial arrhythmia;
  • detecting P waves in wide complex tachyarrhythmias to identify atrioventricular dissociation
  • detect the type of ventriculoatrial conduction during ventricular pacing

Named after Welsh cardiologist Sir Thomas Lewis (1881-1945), Lewis developed and described (1913) his lead configuration to magnify atrial oscillations present during atrial fibrillation.

Lewis lead placement

There are multiple described patterns of Lewis lead placement. In our experience the best way to ‘reveal’ and increase the amplitude of hidden P waves is to move the RA, LA and LL leads, and monitor lead I or II:

  • Right Arm (RA) electrode on manubrium
  • Left Arm (LA) electrode over 5th ICS, right sternal border.
  • Left Leg (LL) electrode over right lower costal margin.
  • Right Leg (RL) electrode in standard position on right leg
  • Monitor Lead I or II

Note: Increasing calibration from 10 to 20mm/mV; and paper speed from 25 to 50mm/second can further amplify the atrial activity.

Lewis Lead electrode placement S5 lead
Lewis lead (S5-lead) placement
Lewis Lead electrode placement S5 lead with heart I II
Lewis lead (S5-lead) placement

Alternate lead positions

The original Lewis description has been modified in various texts and published papers. Alternate placements based on interpretation of the original diagram exist. The most common (as well as simple and rapid to employ) is to change the RA and LA lead only, and monitor lead I:

  • Right Arm (RA) electrode to the right of the sternum at the second intercostal space
  • Left Arm (LA) electrode over 4th ICS just to the right of the sternal border
  • Monitor Lead I
Lewis lead simple switch RA LA only
Lewis lead; simple switch. Monitor Lead I

The right arm electrode is placed in the second intercostal space to the right of the sternum. The left arm electrode is placed in the fourth intercostal space to the right of the sternum. The tracing is then recorded on lead I.

Goldman MJ. Principles of Clinical Electrocardiography 11e. 1982

Clinical examples
Example 1
Lewis lead in wide complex tachycardia Holanda-Miranda 2012
Lewis lead in wide complex tachycardia. Holanda-Miranda 2012

12-lead ECG: showing a wide QRS tachycardia.

Lead I strip: Lewis lead obtained with a paper speed of 50 mm/s and twice normal calibration at 20mm/mV. Regular P waves can now be clearly identified.

Example 2
Lewis lead in Wide QRS Complex Tachycardia Bakker 2009
Lewis lead in Wide QRS Complex Tachycardia. Bakker et al 2009

12 lead ECG: showing a regular broad complex tachycardia of 120 bpm.

Lead I strip: Lewis lead configuration amplifies the P waves in the lead I strip. Atrioventricular dissociation is revealed, confirming the diagnosis of ventricular tachycardia (VT).

History of the Lewis lead

Sir Thomas Lewis (1881-1945) developed and described (1913) his lead configuration to magnify atrial oscillations present during atrial fibrillation.

When fibrillation is present and the electrodes lie in the vicinity of the right auricle (leads 1 and 2 of the diagram), the oscillations are maximal, and there is but a trace of the ventricular beats. When they lie in the long axis of the heart (lead 3), both the oscillations and the ventricular complexes are conspicuous. Finally, when they lie along the left or right ventricular border (leads 4 and 5), the ventricular complexes are clear cut while the oscillations are small or absent.

The corresponding electrocardiograms are shown below the diagram, the first curve of which is from the customary lead II (right arm to left leg). The oscillations of fibrillation are readily identified in this manner and their origin in the auricle is clearly indicated. In tremulous subjects, no oscillations are seen in any of the special leads.

Lewis 1913
Lewis lead original description 1913
A diagram of the chest wall showing the special leads (1 to 5) used in identifying the oscillations of auricular fibrillation; also six electrocardiograms.
Lewis T. Auricular fibrillation 1913

The first electrocardiogram is from lead II; it consists of irregularly placed ventricular complexes (R, T) and of large and continuous oscillations (f f).

The remaining five curves are from the chest wall:

  • 1 and 2 were taken from the area overlying the right auricle — in these leads the oscillations are maximal and the ventricular complexes are minimal
  • 3 was taken from an oblique lead covering the whole heart, and it shows both oscillations and ventricular complexes.
  • 4 and 5 were taken from leads along the margins of the ventricles — they show but little sign of the oscillations


Original articles

Lewis lead in clinical practice

Further reading

Clinical cases (Dr Smith’s ECG blog)



the names behind the name

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

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