OVERSENSING DURING VENTRICULAR PACING IN PATIENTS WITH A 3RD-GENERATION IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR

Objectives. The purpose of this study was to identify the causes of oversensing during ventricular pacing in patients with a third-generation implantable cardioverter-defibrillator. Background. Third-generation implantable cardioverter-defibrillators have the capability for bradycardia pacing as well as antitachycardia pacing and defibrillation. With the Ventritex Cadence Tiered Therapy Defibrillator System, the pulse generator sensitivity is increased during bradycardia pacing to prevent undersensing of an arrhythmia with small amplitude signals. Methods. Records from 85 consecutive patients who underwent implantation of a Cadence device for treatment of ventricular tachyarrhythmias were reviewed. Results. Four patients required continuous pacing for bradyarrhythmias. In three of these patients, ventricular pacing was accomplished using the bradycardia pacing feature of the Cadence device. All three experienced spurious device discharges or had aborted shocks for oversensing. Analysis of real-time and stored electrograms revealed intermittent high frequency, large amplitude noise in two patients and oversensing of maximally gained R and T waves in the remaining patient. No evidence of lead fracture was found in any patient. The problem was solved by implantation of a separate permanent pacemaker in two patients and was partially solved by reprogramming of the device in the remaining patient. Conclusions. Although the Cadence implantable cardioverter-defibrillator has the capability for ventricular pacing in patients with bradyarrhythmias, certain features of its automatic gain control circuit limit its utility in this instance. Oversensing occurs commonly, leading to device discharges or aborted shocks. Implantation of a separate permanent pacemaker may be required in patients who have a Cadence device for tachyarrhythmia control and who also need pacing for bradycardia.