Wednesday, 27 January 2016

ECG of the Week - 25th January 2015 - Interpretation

This week's ECG is another ECG from our patient from last week and the week prior to that. He is an 88yr old male who had an episode of VT on a background of ischaemic cardiomyopathy. Following successful cardioversion he underwent an ICD insertion. He then presented to the Emergency Department complaining of palpitations.




Click to enlarge


Rate:
  • 168
Rhythm:
  • Regular
Axis:
  • LAD
Intervals:
  • QRS - Prolonged (140ms)
Segments:

  • Concordant ST depression in leads V3-6
  • Limb leads show expected discordance

Additional:

  • Regular atrial activity best seen in leads V3-5 in 1:1 ratio with QRS without AV dissociation
  • No precordial concordance
  • RBBB Morphology Rsr' in lead V2
  • Absence of pacing spikes

Interpretation - Broad differentials include:

  • SVT with aberrancy / pre-existing conduction abnormality
    • Clearly different morphology from prior VT seen here
    • Lack of AV dissociation / Concordance
  • VT
    • Prior episode of VT and known cardiomyopathy
    • Not favored due to lack of ICD shock delivery and morphology features noted above - possibility of ICD malfunction should be considered
  • Pacemaker mediated tachycardia
    • Nil evidence of pacing spikes
    • Morphology clearly different when compared with prior v-paced ECG here


What happened ?

The treating clinicians were concerned about the possibility of ICD malfunction and treated the ECG as VT and performed a successful DC cardioversion.

So why didn't the ICD shock the patient ? There are only two simple possibilities:

  • Something is wrong with ICD
  • It's not VT

In this case the ICD didn't fire because this wasn't VT. On pacemaker interrogation this was an episode of atrial tachycardia with aberrant conduction and a further episode whilst an in-patient was terminated with iv sotalol.

References / Further Reading

Life in the Fast Lane

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