Lead Misplacement



    Source: Dr. Adrian Baranchuk Presentation (March 2017) - Queen's University

    Source: John Camm (2007) Europace "Incorrect electrode cable connection during ECG recording" (attached)



    Left Arm - Right Arm Reversal

    • aka LA-RA Reversal
    • One of the most frequent errors made in connecting ECG leads to the patient
    • LA-RA Reversal

      • HINT: Lead I and aVR appear to invert polarity
      • More Specifically:
        • Lead I becomes inverted
        • Leads aVR and aVL switch places
        • Leads II and III switch places
        • aVF unchanged
    • Differential diagnosis is dextrocardia
      • However: in dextrocardia progression of R-wave in precordial leads will be minimal
      • (while in lead reversal it is normal)
    • Example:

    Left Arm - Left Leg Reversal


    • LA-LL Reversal
    • Usually very challenging to pick up!!!
    • LA-LL Reversal

      • HINT: Amplitude of P-wave in lead I > lead II
      • P-wave terminal +'ve component in lead III

      More Specifically:

      • Lead III becomes inverted
      • Leads I and II switch places
      • aVL and aVF switch places
      • aVR unchanged
    • Confirmation with second ECG is usually required
    • Example:


    Right Leg - Left/Right Arm Reversal 

    • RL-LA or RL-RA Reversal
    • Result is ZERO potential difference between the legs.
    • RL and one of the arms (LA or RA) reversal:

      • RL-RA --> Asystole pattern in Lead II
      • RL-LA --> Asystole pattern in Lead III


      More Specifically:

      • RL-RA
        • Leads aVR and aVF become identical.
        • Lead II records a flat line (zero potential).
        • Lead III is unchanged.
        • Lead aVL approximates an inverted lead III.
        • Lead I becomes an inverted lead III.
      • RL-LA
        • Lead III records a flat line (zero potential)
        • Lead I and II are identical
        • aVL and aVF are identical
        • Lead II is unchanged
        • aVR is close to inverted Lead II
    • Example RL-LA Reversal:

    Precordial Lead Reversal

    • The most common is V1 / V6 reversal 
    • Precordial Lead Reversal

      • R-wave progression: Normally R-wave increases in amplitude V1 to V6, and S-wave becomes smaller
      • In reversal, you see a sudden jump in R-wave and S-wave amplitudes (or ones that don't make sense)
        • i.e. deep S-wave in V6 and tall R-wave in V1 would make you suspicious.
    • Potential diagnostic misinterpretations:
      • RBBB
      • Old posterior MI
      • RVH
      • L-sided accessory pathways
    • Example:

    Electrodes On The Torso

    • There are reasons to place electrodes on the torso instead of on limbs. 
    • During an emergency, clinicians can place electrodes on the torso to save time undressing the patient. 
    • Usually, it allows the correct ECG diagnosis, but has drawbacks:
    • Effects:
      • "Pseudo-Q-waves" and "pseudo-ST elevation" in INFERIOR leads (can be interpreted as MI)
      • Increased QRS amplitude
    • Example:

    Telemetry Interference

    • A common mistake is to place telemetry electrodes on top of ECG electrodes (or vice versa).
    • This creates distortion of the ST segment mimicking ST elevation or arrhythmias. 
    • Example:


    Patient Sitting at 90°

    • Some situations (like decompensated HF, respiratory insufficiency) where ECG is done sitting upright  (or semi-Fowler's position)
    • This affects QRS axis and QRS amplitude:
    • QRS amplitude reduction in lead III (lead most sensitive to diaphragm position)
    • Example:
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