COMBINED 3RD-GENERATION IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR WITH PERMANENT UNIPOLAR PACEMAKERS - PRELIMINARY-OBSERVATIONS

As implantable cardioverter defibrillators (ICDs) are strictly contrai ndicated in the presence of unipolar pacemakers, currently available o ptions in patients having such chronic pacing systems include: abandon ing the implanted pacemaker and selecting an ICD with ventricular dema nd (VVI) pacing; or replacing the chronic (dual chamber) unipolar paci ng system with a dedicated bipolar version prior to ICD implantation. In three patients with previously implanted unipolar pacemakers, we ch allenged the premise that all ICD systems are incompatible by combinin g with a third-generation transvenous ICD system (Medtronic 7217B PCD( R)) incorporating true bipolar sensing, a self-limiting auto-adjusting sensitivity, and a tolerant VF detection algorithm, The potential for pacemaker-ICD interaction was minimized by separating the tip of the ICDs transvenous right ventricular pace/sense-defibrillation coil lead from that of the chronic pacemaker lead by greater than or equal to 2 -3 cm, and by performing ''worst case'' intraoperative testing. Althou gh ICD double-counting of the dual chamber pacemaker's atrial and vent ricular pacing spikes could be provoked at extreme high output setting s, it did not occur at clinically appropriate settings. More important ly, continuous high output asynchronous pacing during ventricular fibr illation (VF) did not interfere with ICD detection. During a mean foll ow-up period of 18 months, one patient has had VF appropriately termin ated by the ICD. In the remaining two patients, proper VF detection an d ICD function was reassessed at 3 months and/or at 1 year during noni nvasive testing. Conclusion: These preliminary findings demonstrate th at this transvenous ICD system's VF sensing and detection features com bined with careful implant technique, rigorous ''worst case'' testing for possible pacemaker-ICD interaction with regular follow-up, may per mit implantation of this ICD system in patients with chronic unipolar pacing systems. Further studies are needed to validate the long-term c linical safety of this promising revised approach to a currently contr aindicated device combination.