Asymptomatic adult patient. Routine ECG. Describe the ECG.

Describe and interpret this ECG


Main Abnormalities

This ECG is a classic example of limb lead misplacement with a left arm / right arm lead reversal:

  • Positive P-QRS-T in lead aVR
  • Inverted complexes in leads I and aVL
  • Normal complexes in the precordial leads rules out dextrocardia (compare this to ECG Quiz 024)

The most obvious abnormality on this ECG is the positive QRS complex in aVR. This is unusual and should always prompt a search for additional evidence of limb lead misplacement.


Effects of LA-RA lead reversal

Switching the LA and RA electrodes produces the following effects:

  • Lead I becomes inverted
  • Leads II and III switch places
  • Leads aVL and aVR switch places (hence aVR becomes positive, aVL negative)
  • Lead aVF remains unchanged

This concept is explained in more detail here

TOP 100 ECG Series

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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