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
With reversal of the LA and RA electrodes, Einthoven’s triangle flips 180 degrees horizontally around an axis formed by lead aVF.
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.
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.
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.
With reversal of the RA and LL electrodes, Einthoven’s triangle rotates 180 degrees vertically around an axis formed by aVL.
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.
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
Should be suspected when a very small voltage is recorded (
ECG is unchanged in LL/N reversal!!
Bilateral arm-leg reversal: