ECG Case 194: Interpretation

This post is an answer to the ECG Case 194

  • Rate: ~175 / min
  • Rhythm:
    • Regular
    • No p waves visible
  • Axis:
    • Extreme Axis Deviation

  • Intervals:
    • PR – No P waves visible
    • QRS – Prolonged (160-200ms)
  • Additional:
    • Pacing Spikes Visible Intermittently
    • Pacing Spikes Interval 1000ms (60 bpm)
    • No evidence of pacing capture or fusion
    • Spikes best seen Leads II, aVR, V5/6
    • No concordance
ECG Case 194


  • Broad Complex Tachycardia
  • Consistent with Ventricular Tachycardia
    • Patient Age
    • Extreme Axis Deviation
    • Broad – broad QRS
    • Not typical BBB morphology
  • Pacing Spikes – Pacer set to VVIR according to old notes
  • ? Failure to sense and capture

This patient had a pacemaker inserted 7 years prior to this presentation.
Pacemaker settings:

  • Single lead placed in right ventricle
  • Pacing mode set to VVIR
  • Rate setting 60 – 110 bpm

Why it isn’t Pacemaker Mediated Tachycardia (PMT)

  • It can not be a paced rhythm or PMT because of the RBBB morphology unless there is a lead in the left ventricle.
  • You need a dual chamber device programmed to at least DDD.
  • Results from retrograde conduction of a V paced event sensed as an A and thus tracked over and over.
  • The rate of PMT is at or below the upper tracking rate which is not the case here.

The presence of ‘Pacing Spikes’

  1. Artefactual – Mostly likely by consensus
  2. The device is at End of Life and is defaulted to VOO mode at 60 bpm – Possibility
  3. The device battery is low and there is a magnet over it thus making it VOO.  The magnet rate is usually 85 or 100 bpm unless the battery is low – Possibility
  4. The device is at ERI (elective replacement, low battery and thus switched to VVI) and is pacing VVI with loss of sensing – Unlikely