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Lead misplacement & artefact

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CONTENTS

limb lead reversals & related artefact

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general clues to limb lead reversal may include:

  • 🚩 Lead I and V6 look totally different (they should have similar morphology).
  • 🚩  Lead I is completely inverted (P, QRS, and T).
  • 🚩  One of the leads is a flat line (typically one of the leads I, II, or III).
  • 🚩 Lead III is completely inverted & markedly different from aVF. ⚡️
LA/RA reversal (technical dextrocardia)
  • Key clues:
    • Lead I is completely negative (P wave, QRS complex, and T wave).
    • Lead I doesn't match V6 (precordial leads are normal).
    • Lead aVR often becomes positive (which is very atypical).
    • There may be marked right-axis deviation. 🌊
  • Additional findings:
    • Leads II and III switch places.
    • Leads aVL and aVR switch places.
    • Lead aVF remains unchanged. 🌊
  • Differential:
    • [1] True dextrocardia (below; diagnosed primarily based on precordial leads).
    • [2] RA/RL reversal can mimic this ⚡️

true dextrocardia

  • Right axis deviation:
    • Lead I is net negative (often with a prominent S-wave).
    • Lead I is often completely negative (including a negative P-wave).
  • Horizontal axis:
    • Reverse R-wave progression (decreasing R-wave amplitude from V1 –> V6).
      • R-wave in V1 > R-wave in V2.
      • R-wave in V1 is unusually prominent.
    • Low voltage seen in left precordial leads.
  • ⚠️ Dextrocardia may invalidate the remainder of the ECG interpretation. Once dextrocardia has been identified, a new ECG should be obtained with all the leads flipped to the other sides (including V1R-V6R, and swapping the right/left arm and leg leads). This new ECG may be interpreted in the standard fashion.
True dextrocardia. (31496498)
LA/LL reversal 
  • Key clues:
    • Lead III is inverted (P wave, QRS complex, and T wave). However, since Lead III generally has a varying polarity, this inversion may not be apparent. A negative P-wave in lead III may be a helpful clue.
    • The P-wave is larger in lead I than in lead II (usually the other way around). 🌊
  • Additional findings:
    • Leads I and II switch places.
    • Leads aVL and aVF switch places.
    • Lead aVR remains unchanged. 🌊
LA/LL lead misplacement. Lead I doesn't match V6 at all, which may be the first sign of misplacement. The P-wave in I is larger than the P-wave in II, and lead III is entirely negative. (Dr. Smith's ECG blog)
RA/LL reversal
  • Key clues:
    • Leads I, II, III, and aVF are all completely inverted (P wave, QRS complex, and T wave).
      • Lead II becomes inverted.
      • Leads I and III become inverted and switch places.
    • Lead aVR is upright. 🌊
      • Leads aVR and aVF switch places.
  • Additional findings:
    • Lead aVL is unchanged. 🌊
RA/RL reversal
  • Key clues:
    • Lead II is a nearly flat line. 🌊
    • Lead I becomes an inverted lead III (may mimic technical dextrocardia).
    • Leads aVR and aVF become identical.
  • Additional findings:
    • Lead III is unchanged.
    • Lead aVL approximates an inverted lead III. 🌊
LA/RL reversal
  • Key clues:
    • Lead III is a flat line. 🌊
  • Additional findings:
    • Lead I becomes identical to lead II.
    • Lead II is unchanged.
    • Lead aVR approximates to an inverted lead II.
    • Leads aVL and aVF become identical. 🌊
LA-LL plus RA-RL reversal
  • Key clues:
    • Lead I is a flat line. 🌊
  • Additional findings:
    • aVR and aVL become identical.
    • Leads II, III, and aVF become identical. 🌊

Attribution: This section has been largely copied from an excellent chapter in Life In The Fast Lane, which the reader is referred to for additional details: 🌊

precordial lead reversals

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A major principle to recognizing lead misplacement (or sometimes artifact) is incongruity between neighboring leads.  Generally, neighboring leads should have somewhat similar morphology.  If two neighboring leads are displaying totally different morphology, something is wrong.  

loss of R-wave and P-wave transition from V1 –> V6

  • R-waves should smoothly increase in size from V1 –> V6
  • P-wave transition:
    • V1:  P-wave often has at least some negativity (e.g., biphasic)
    • With progression across the precordium, it often becomes monophasic positive.
    • If there are irregular jumps in P-wave morphology, this reveals lead misplacement (example below).

artifacts related to physical movement

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  • Movement during the ECG will lead to artifacts.
  • Parkinsonian tremor is a common source of artifact, which may mimic atrial flutter.
  • Clues to help identify movement artifacts:
    • Movement artifacts usually aren't synchronized with the pulse, so the QRS complexes may “march through” the artifact at a dissociated rate.
    • Limb movement artifacts may affect some limb leads while leaving others relatively normal.
pulse tapping artifact

This is caused if one limb lead is placed over a pulsating artery.

  • Among Leads I, II, and III:
    • One of them will be stone-cold normal.
    • The other two will look really weird.
    • There is a dramatic morphological distinction between the one normal-looking lead and the two weird ones.
  • The remainder of the ECG also looks weird (limb leads are more affected than the precordial leads).
  • Leads I and V6 often look wholly different (this is a general sign of artifact or lead misplacement of some sort).
Pulse tapping artifact – note how Lead I is normal. (Dr. Smith's ECG blog)
Pseudo-pulse tapping artefact: At first this might look like pulse tapping artefact, because morphology is very abnormal in the ECG and looks more normal in I. However, Lead I has some abnormality and resembles lead V6 – so this is not an artifact (the patient had diffuse subendocardial ischemia). (Dr. Smith's ECG blog)

questions & discussion

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To keep this page small and fast, questions & discussion about this post can be found on another page here.

References

  • 31496498 Mozayan C, Levis JT. ECG Diagnosis: Dextrocardia. Perm J. 2019;23:18-244. doi: 10.7812/TPP/18.244 [PubMed]

The Internet Book of Critical Care is an online textbook written by Josh Farkas (@PulmCrit), an associate professor of Pulmonary and Critical Care Medicine at the University of Vermont.


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