Ventricular undersensing and proarrhythmia

N° 2
Manufacturer Boston Scientific Device PM Field Sensing
  • 81-year-old man
  • Single-chamber pacemaker (Boston Scientific) for slow symptomatic atrial fibrillation
  • Hospitalization for exploration of acute pain of the left hypochondrium
  • Two days after admission, while undergoing an abdominal ultrasound, cardiac arrest
  • After 10 minutes of cardiac massage and 2 external electric shocks, the patient recovered proper hemodynamics
  • Tracing recorded at the time of the episode
Graph and trace
  • Ventricular undersensing and pacing on the T wave
  • Induction of a fast, polymorphous and spontaneously resolving ventricular arrhythmia
  • Ventricular undersensing and pacing on the T wave
  • Induction of a VF episode (disorganized ventricular arrhythmia)
  • Marked ventricular undersensing of the arrhythmia
  • This tracing is quite rare since it shows the induction of ventricular fibrillation following ventricular undersensing and asynchronous pacing during the ventricular vulnerable period (R-on-T phenomenon)
  • This is the more frightened complication associated with ventricular undersensing
  • The risk of ventricular fibrillation is very rare outside of circumstances such as myocardial ischemia or metabolic disorder
  • This patient underwent 2 electric shocks which allowed termination of the arrhythmia
  • The interrogation of the device revealed a drop in impedance associated with a significant rise in the pacing threshold suggestive of lead failure
  • A new lead was implanted and the patient was able to be discharged home
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