Lead change


Incorrect electrode cable connections during electrocardiographic (ECG) recording can simulate rhythm or conduction disturbance, myocardial ischaemia and infarction, as well as other clinically important abnormalities.

Limb electrodes misplacement

When the limb electrodes (LA, RA, LL) are exchanged without disturbing the neutral electrode (RL,N), Einthoven triangle is “flipped” 180 degrees or rotated, resulting in leads that switch positions, become inverted or remain unchanged (depending on their initial position and vector). 

Bipolar leads: I, II, III

Augmented unipolar leads: aVL, aVF, aVR

Wilson’s central terminus: the “zero” lead, produced by averaging signals from the limb electrodes

By Npatchett - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=39235282

Einthoven’s triangle 


LA/RA reversal 

With reversal of the LA and RA electrodes, Einthoven’s triangle flips 180 degrees horizontally around an axis formed by lead aVF.

  • Lead I becomes inverted
  • Leads II and III switch places
  • Leads aVL and aVR switch places
  • Lead aVF remains unchanged


P, QRS, and T predominantly downgoing in lead I

P, QRS, T upgoing in lead aVR

Precordial leads unaffected


LA/RA reversal may simulate dextrocardia. Normal-appearing V leads in the 12-lead ECG suggest limb lead reversal rather than dextrocardia.

LA/LL reversal 

In reversal of the LA/LL electrodes, Einthoven's triangle rotates 180° vertically around an axis formed by aVR.


 What is reading as lead I is truly lead II, lead II is truly lead I, and lead III is reversed in polarity.

  • Lead III becomes inverted.
  • Leads I and II switch places
  • Leads aVL and aVF switch places
  • Lead aVR remains unchanged


  • the P wave has a larger voltage in I than II (90% sensitivity and 38% specificity)


 LA/LL reversal has the potential to create a pseudo‐inferior wall infarct pattern on the ECG.

 LA/LL reversal also causes inverted P waves in III. This is an important clue to determine the presence of a lead reversal. Frequently this error will lead to a near isoelectric line in leads I, II, or III; which might be the only sign of LA/LL lead reversal.


RA/LL reversal

With reversal of the RA and LL electrodes, Einthoven’s triangle rotates 180 degrees vertically around an axis formed by aVL.

  • Lead II becomes inverted.
  • Leads I and III become inverted and switch places.
  • Leads aVR and aVF switch places.
  • Lead aVL is unchanged.


 Leads I, II, III and aVF are all completely inverted

Lead aVR is upright

The RA/LL electrode reversal may cause pseudo‐inferior myocardial infarction. However, unlike inferior infarction in sinus rhythm, P waves in leads aVF and II are also inverted. Lead II, I, and III become inverted, leads I and III switch places, leads aVR and aVF switch places, and lead aVL is unchanged. 

LA/N reversal 

 the LA/LL electrodes record almost identical voltages

normally perpendicular to aVR is ≈lead III, in RL/N reversal perpendicular to aVR becomes ≈lead II

 Lead I becomes identical to lead II

  • Lead II is unchanged
  • Lead III has a flat line (zero potential)
  • aVR approximately to an inverted II
  • aVL and aVF become identical
  • precordial leads may be distorted


RA/N reversal 

Should be suspected when a very small voltage is recorded (

  • Lead I becomes an inverted lead III.
  • Lead II records a flat line (zero potential).
  • Lead III is unchanged.
  • Lead aVL approximates an inverted lead III.
  • Leads aVR and aVF become identical
  • precordial leads may be distorted


Arms and legs reversal or bilateral arm‐leg reversal (LA/L and RA/L)

ECG is unchanged in LL/N reversal!!

Bilateral arm-leg reversal:

  • Lead I = zero voltage
  • Leads II, III, and aVF become identical (equivalent to inverted lead III)
  • Leads aVL and aVR appear exactly alike 
  • precordial leads may be distorted




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