Can a follow-up 12-lead (twelve-lead) electrocardiogram (ECG) show whether the previous ECG had a left arm lead reversal?

Detecting Left Arm Lead Reversal Using Follow-up ECGs

Yes, a follow-up 12-lead ECG can reveal whether a previous ECG had a left arm lead reversal by comparing the characteristic pattern differences between the two recordings. 1

How Lead Reversals Affect ECG Patterns

When the left arm lead is reversed with another lead, specific pattern changes occur that can be identified by comparing with a properly recorded ECG:

• Left arm-right arm reversal:

  • Inversion of limb lead I
  • Switch of leads II and III
  • Switch of leads aVR and aVL
  • aVF remains unaltered
  • Precordial leads remain unchanged (central terminal unaffected) 1

• Left arm-left leg reversal:

  • Subtle shift in axis
  • Inversion of lead III
  • Changes in P-wave morphology in limb leads 1, 2

Key Diagnostic Features to Compare Between ECGs

When comparing a follow-up correctly recorded ECG with a previous one that may have had a left arm lead reversal:

1. Lead I morphology: In normal situations, lead I should be generally similar to V6 regarding P wave morphology and QRS direction 1

2. Discordance between leads: A significant discordance between lead I and V6 suggests lead misplacement rather than a true cardiac abnormality 1

3. Precordial lead consistency: Since limb lead reversals don't affect precordial leads, these should remain consistent between recordings 1

4. P-wave patterns: Changes in P-wave morphology across limb leads can help identify left arm-left leg reversals 1

Clinical Implications and Pitfalls

Limb lead switches can result in:

• False-positive signs of ischemia
• False-negative signs of ischemia
• Mimicking high lateral wall infarction in a case with inferior wall infarction 2
• Misdiagnosis of ST-segment elevation myocardial infarction (STEMI) 3

Verification Process

When suspecting a previous left arm lead reversal:

1. Compare the follow-up ECG with the previous one, focusing on the pattern changes described above
2. Look for sudden, unexplained changes in ECG morphology between recordings without clinical correlation
3. Verify that the follow-up ECG shows expected normal relationships between leads (lead I similar to V6)
4. Check for resolution of any unusual or unexpected diagnostic patterns seen in the previous ECG

Advanced Detection Methods

For complex cases or when uncertainty exists:

• Mathematical reconstruction methods can be used to simulate what the correct ECG should look like 4
• The "REVERSE" mnemonic can help identify patterns suggestive of lead reversal 3
• Artificial neural networks have shown high sensitivity (99.1%) for detecting right/left arm lead reversals 5

Remember that proper electrode placement is crucial for accurate ECG interpretation, and variations in lead placement can result in significant diagnostic errors 6. When a lead reversal is suspected, the ECG should be repeated with careful attention to proper lead placement and technique.