title: Combined third-generation implantable cardioverter defibrillator with permanent unipolar pacemakers: preliminary observations.
abstract: As implantable cardioverter defibrillators (ICDs) are strictly contraindicated in the presence of unipolar pacemakers, currently available options in patients having such chronic pacing systems include: abandoning the implanted pacemaker and selecting an ICD with ventricular demand (VVI) pacing; or replacing the chronic (dual chamber) unipolar pacing system with a dedicated bipolar version prior to ICD implantation. In three patients with previously implanted unipolar pacemakers, we challenged the premise that all ICD systems are incompatible by combining with a third-generation transvenous ICD system (Medtronic 7217B PCD) 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 > or = 2-3 cm, and by performing "worst case" intraoperative testing. Although ICD double-counting of the dual chamber pacemaker's atrial and ventricular pacing spikes could be provoked at extreme high output settings, it did not occur at clinically appropriate settings. More importantly, continuous high output asynchronous pacing during ventricular fibrillation (VF) did not interfere with ICD detection. During a mean follow-up period of 18 months, one patient has had VF appropriately terminated by the ICD. In the remaining two patients, proper VF detection and ICD function was reassessed at 3 months and/or at 1 year during noninvasive testing.
  
  
  CONCLUSIONS
  These preliminary findings demonstrate that this transvenous ICD system's VF sensing and detection features combined with careful implant technique, rigorous "worst case" testing for possible pacemaker-ICD interaction with regular follow-up, may permit implantation of this ICD system in patients with chronic unipolar pacing systems. Further studies are needed to validate the long-term clinical safety of this promising revised approach to a currently contraindicated device combination.
authors.affiliation: Division of Cardiology, St. Elizabeth's Medical Center, Boston, MA 02135, USA.
authors.forename: C
authors.initials: C
authors.lastname: Haffajee
authors.forename: D
authors.initials: D
authors.lastname: Casavant
authors.forename: P
authors.initials: P
authors.lastname: Desai
authors.forename: R
authors.initials: R
authors.lastname: Moon
authors.forename: P
authors.initials: P
authors.lastname: Voukydis
authors.forename: P
authors.initials: P
authors.lastname: Pacetti
mesh_terms: D000368:Aged; D000465:Algorithms; D000075202:Contraindications; D017147:Defibrillators, Implantable; D004562:Electrocardiography / Q000295:instrumentation; D004567:Electrodes, Implanted; D004867:Equipment Design; D005260:Female; D006327:Heart Block / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D012984:Software; D017180:Tachycardia, Ventricular / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000150:complications / Q000503:physiopathology / Q000628:therapy*