COMPARISON OF OVERSENSING DURING BRADYCARDIA PACING IN 2 TYPES OF IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR SYSTEMS

Background During bradycardia pacing in Ventritex Cadence (Models V-10 0 and V-110) implantable cardioverter-defibrillators, amplifier gain i s maximal and oversensing and false tachyarrhythmia detection have bee n reported. Newer Ventritex devices (Cadet, Model V-115 and Contour, M odel V-145) have a modified automatic gain control that may minimize o versensing. Methods and Results We prospectively studied 50 patients ( 22 with Cadence, 28 with Cadet or Contour). Electrograms were evaluate d for oversensing during bradycardia pacing. The bradycardia pacing re fractory period required to prevent oversensing of T waves of paced be ets and the time and number of beats required to achieve minimum gain after cessation of pacing were assessed. The bradycardia pacing refrac tory period could be left at its default setting of 350 ms in only 15 (30%) of 50 patients. The mean bradycardia pacing refractory period re quired to avoid oversensing of paced T waves was 386 +/- 32 ms. During pacing, oversensing of nonpaced T waves was seen in 12 (24%) devices, with similar incidence in Cadence devices (18%) and Cadet and Contour devices (29%, p = not significant). The time and number of beats to a chieve minimum gain after pacing were longer in Cadence devices (19.0 +/- 4.5 vs 4.6 +/- 1.2 sec; 21.3 +/- 3.3 vs 5.0 +/- 0.4 beats, both p < 0.001). Conclusions The incidence oi oversensing ai maximum goin is similar in bath types of devices, but more rapid changes in autogain l evels in the newer devices may reduce the likelihood of false tachyarr hythmia detection.