Unusual cause for an increase of the sensing integrity counter in a patient with inappropriate implantable cardioverter-defibrillator therapy

We describe the case of a patient who presented with multiple implantable cardioverter-defibrillator (ICD) shock discharges 12 months after device implantation. Upon device interrogation, intermittent oversensing of electrical noise and potential ICD lead failure were suggested by a significant increase in the sensing integrity counter (SIC), a cumulative count of very short ventricular sensed intervals. Analysis of stored episodes, however, revealed that inappropriate ICD therapy had been caused by intermittent T-wave oversensing (TWO), and that the increase of the SIC resulted from the coincidence of TWO and premature ventricular complexes (PVCs). T-wave oversensing resolved and the SIC did not increase any more during follow-up after adjustment of ventricular sensitivity. The coincidence of TWO and PVCs should therefore be considered as an uncommon cause for short ventricular sensed intervals in ICD patients presenting with a suspect increase in the SIC.