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 ov ersensing during ventricular pacing in patients with a third-generatio n implantable cardioverter-defibrillator. Background. Third-generation implantable cardioverter-defibrillators have the capability for brady cardia pacing as well as antitachycardia pacing and defibrillation. Wi th the Ventritex Cadence Tiered Therapy Defibrillator System, the puls e generator sensitivity is increased during bradycardia pacing to prev ent undersensing of an arrhythmia with small amplitude signals. Method s. Records from 85 consecutive patients who underwent implantation of a Cadence device for treatment of ventricular tachyarrhythmias were re viewed. Results. Four patients required continuous pacing for bradyarr hythmias. In three of these patients, ventricular pacing was accomplis hed using the bradycardia pacing feature of the Cadence device. All th ree experienced spurious device discharges or had aborted shocks for o versensing. Analysis of real-time and stored electrograms revealed int ermittent high frequency, large amplitude noise in two patients and ov ersensing 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 patie nts and was partially solved by reprogramming of the device in the rem aining patient. Conclusions. Although the Cadence implantable cardiove rter-defibrillator has the capability for ventricular pacing in patien ts with bradyarrhythmias, certain features of its automatic gain contr ol circuit limit its utility in this instance. Oversensing occurs comm only, 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 fo r bradycardia.