Permanent Pacing via Implantable Defibrillators

The addition of the VVI antibradycardia pacing capability to the implantable cardioverter defibrillator (ICD) represented a significant advance. Postshock bradyarrhythmias became less of a concern, and sudden death due to asystole could be prevented. However, because of hemodynamic limitations imposed by fixed rate VVI mode and significant current drain, it has been common practice to use separate physiologic pacemakers in ICD patients requiring more than occasional backup pacing. ICDs capable of dual chamber, rate responsive pacing promise to largely eliminate the need for a separate pacemaker. Potential advantages include fewer intravascular leads, elimination of device-device interactions, better cosmetic results, and simplified follow-up. Early experience with these systems has been favorable. Improved tachyarrhythmia discrimination and relief of pacemaker syndrome following upgrade from single to dual chamber ICDs have been reported. Addition of full-featured pacing is technically complex, and the resultant product is not simply the sum of a DDDR pacemaker and a tiered-therapy ICD. As clinical experience expands, device shortcomings and idiosyncrasies are becoming apparent. Compromises have been made between pacing versatility and safe defibrillator function. The emphasis on defibrillation safety may, at times, result in suboptimal pacemaker function. In this article, we describe potential problems and provide guidelines for their prevention at the time of implant (and initial programming) and during follow-up. Problems occurring with single chamber ICDs are discussed when anticipated with dual chamber units of similar operation. Need for Antibradycardia Pacing in ICD Recipients In the past, 15%–20% of patients with ICDs required a separate pacemaker. Geelen et al. reported that permanent pacing was required in 25 (18%) of 139 consecutive ICD patients. This included 10 patients with a preexistent pacemaker, 10 patients in whom the indication for pacing became evident at the time of ICD implantation, and 5 patients who became pacemaker dependent during follow-up. Iskos et al. analyzed the need for a subsequent dual chamber pacemaker in 224 patients with ICDs capable of VVI pacing. Twentytwo (10%) patients received dual chamber pacemakers (mean interval from ICD to pacemaker implant of 2.5 years). A history of atrial tachyarrhythmia and treatment with antiarrhythmic drugs before ICD implantation were significant predictors of a subsequent need for physiologic pacing. Higgins et al. reviewed 122 consecutive patients undergoing ICD implantation or replacement and concluded that a dual-chamber ICD could have been of value in 55% of patients. Strict criteria for dual chamber pacing were present in 29%. A Mayo Clinic review of 253 patients revealed that a dual chamber ICD would have been definitely indicated in 11% of patients, probably indicated in 28%, and possibly indicated in 14%. Candidacy rates will increase greatly if biventricular pacing proves beneficial for patients with heart failure. Jung and Lüderitz observed that the frequent need to add drugs with negative chronotropic effects (e.g., amiodarone, sotalol) in patients with ICDs implanted for ventricular tachycardia (VT) may justify use of a dual chamber ICD system in some patients without bradycardia documented at baseline. Industry surveys estimate that, in 1999, 50% of the ICDs implanted in the U.S. and 30% of those implanted in Europe had dual chamber pacing capabilities.