Wednesday, 30 November 2016

ECG of the Week - 28th November 2016 - Interpretation

The following ECG's are from a 62 yr old female who presented with chest and epigastric pain. The first ECG was performed by the patient's GP and the second ECG on arrival in the Emergency Department. Her pain was ongoing at the time of both ECG's and she has a past medical history of hypertension, obesity and T2DM.

ECG from GP
Click to enlarge
Key features:

  • Rate 96 bpm
  • Regular sinus rhythm
  • Normal Axis
  • Normal Interval
  • Normal ST Segments
  • Biphasic / Inverted T wave in lead III

ECG on arrival ED
Click to enlarge
Compared with earlier ECG there is new:

  • Right axis deviation - new compared with above
  • Leads aVR & lead I complete inversion i.e. negative P wave / QRS complex / T wave
  • Flat aVR with morphology very different to V1
  • Other features unchanged - rate, rhythm, intervals, ST segments


  • Multiple features suggesting RA / LA lead reversal
    • Complete inversion of leads aVR and I 
    • New axis change between serial ECG's

Remember RA / LA reversal results in:

  • Inversion of lead I
  • Leads II & III swap places
  • Leads aVR & aVL swap places

What happened ?

This all seemed very straight forward until we reviewed the patient and found all the leads to be in the correct position !!
Remember ECG's are complicated machines with multiple connections and just because the one connection with the patient appears to be correct doesn't mean there isn't a problem elsewhere. So we removed the ECG machine from the situation, the patient was completed disconnected from the usual machine and a new recording was performed on a portable ECG machine, i.e everything in the process after the patient was replaced. The following ECG is below:

ECG repeated on different ECG machine
Click to enlarge
Comparing with the prior ECG's we can see resolution of the complete lead inversion and axis change seen in the second ECG with the overall morphology similar to the ECG performed at the GPs. I suspect the change in appearance of aVL between the 1st and 3rd ECG reflects both patient and lead positioning during ECG recording.
It turned out the culprit was a damaged cable connection between the patient leads and ECG monitor unit !!

References / Further Reading

Life in the Fast Lane

  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.

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