Ventricular undersensing and proarrhythmia

Tracing

N° 2

Manufacturer Boston Scientific Device PM Field Sensing

Patient

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

Comments

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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