This ECG was recorded from a 21-year old female who had complained of palpitations. On examination she had an ejection systolic murmur.

What is the most likely explanation for the abnormal ECG appearances?


Well, it looks like my clue was useful to a few people. Others may have recognised the pattern or worked it out for themselves, but what happened is that the left arm and V2 connections were swapped for this ECG. The typical features of this technical error have been documented but I suspect that it usually goes unrecognised. The key ECG characteristics, all on show in this recording, are:

  • Deep S waves in leads I and aVL
  • Tall R waves in leads III and aVF
  • T wave inversion in III and aVF
  • Lead V2 looks ‘wrong’ and doesn’t fit in with the usual progression from V1 to V3. In our example, V2 has a negative T wave whereas its immediate neighbours, V1 and V3, both have a positive T wave.

Note that lead II is entirely unaffected by the error; the other 11 leads are all altered. The effects of this connection swap can easily be appreciated when you compare the original ECG with this one, which was recorded after the error had been corrected. It is now completely normal.

Dr Dave Richley, 
Associate Lecturer
Newcastle University

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