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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
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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:
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Left Arm - Left Leg Reversal
- LA-LL Reversal
- Usually very challenging to pick up!!!
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LA-LL Reversal
- HINT: Amplitude of P-wave in lead I > lead II
and/or - 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
- HINT: Amplitude of P-wave in lead I > lead II
- Confirmation with second ECG is usually required
- Example:
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Right Leg - Left/Right Arm Reversal
- RL-LA or RL-RA Reversal
- Result is ZERO potential difference between the legs.
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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:
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Precordial Lead Reversal
- The most common is V1 / V6 reversal
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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:
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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:
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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:
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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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