Paradoxical undersensing due to quiet timer blanking.

A case of undersensing of atrial activity by a dual chamber pacemaker is presented. Programming to more sensitive voltages exacerbated undersensing, and programming to less sensitive levels resolved the undersensing. The mechanism by which pacemaker sense amplifiers function to create apparent paradoxical undersensing is reviewed.

Impaired detection of ventricular tachyarrhythmias by a rate-smoothing algorithm in dual-chamber implantable defibrillators: intradevice interactions.

Introduction: Rate smoothing is an algorithm initially designed to prevent rapid changes in pacemaker rates. In this study, we sought to determine the potential of the rate-smoothing mechanism in preventing detection of ventricular tachyarrhythmias.

Methods And Results: Clinical testing of rate smoothing was performed at the time of defibrillator arrhythmia induction in 16 patients with implantable defibrillators during 65 episodes of ventricular tachyarrhythmias.