ECG of the Week – 1st April 2020 – Interpretation

Posted on by

You have been asked to review the ECG below, of an 89 year old woman who has presented with vomiting and lethargy for 2 days. The treating nurse has informed you that she has leg cellulitis. Observations are T39.3, P72, BP 110/51, BSL 9, RR 16, Sats 94% air.

Interpretation:

  • Rate: 78
  • Rhythm: Sinus arrythmia
  • Axis: -90 to +180 (3 lead analysis) = Extreme axis
  • Morphology:
    • P wave inversion I, aVL, lead 1,
    • STE 2mm lead I
    • T wave inversion V5-6
    • Biphasic T waves V3-V4
  • Intervals: PR variable 160 ms, 200ms in complexes 3,7,11 (ectopic atrial beats)
  • Summary: Lead reversal RA/ LA

Interpretation continued:

When to suspect Limb Electrode Reversal:

  • QRS axis is unexpectedly abnormal
  • P waves are inverted in limb leads, especially lead I and II
  • aVR is upright and another leads resembles aVR
  • leads I,II,III are virtually a flat line
  • IN THIS CASE: II and III are reversed, aVR and aVL are reversed, I is -ve

When to suspect Chest Electrode Reversal:

  • normal P, QRS,T progression across the precordium is interrupted

Electrode Reversal in general

    • 10 electrodes (RA/RL/LA/LL/V1-6) produce a 12 lead ECG
    • Limb electrodes contribute to leads APART from RL which acts to eliminate artefact.
    • Leads I,II,II are obtained by combining the output of two limb electrodes.
    • aVL, aVF, aVR compare a single lead electrode by comparing to a ‘common’ electrode that is the sum of the two remaining limb electrodes.
    • Chest electrodes also use a ‘common’ electrode for comparison by combining the three limb electrodes (RA,LA,LL) this means if limb electrodes are reversed it will not affect chest leads.