title: Reduction of right ventricular pacing in patients with dual-chamber ICDs.
abstract: BACKGROUND
  Unnecessary right ventricular (RV) pacing in patients with implantable cardioverter defibrillators (ICD) may adversely affect heart failure morbidity and total mortality. Inhibition of Unnecessary RV Pacing with AV Search Hysteresis in ICDs (INTRINSIC RV) is a prospective, multicenter, randomized trial evaluating outcomes in ICD recipients programmed to single-chamber pacing (VVI) versus dual-chamber (DDDR) pacing with AV search hysteresis (AVSH).
  
  
  METHODS
  Patients underwent ICD implant (for standard indications). The ICD was programmed to DDDR with AVSH regardless of any need for pacing. Rate-adaptive pacing was set at 60-130 ppm with dynamic AV delay from 200 to 90 ms. AVSH was programmed to search every 32 intervals and extend the AV delay by 50%. One week post-implant patients with ICDs were interrogated to assess the percentage of RV pacing with the expectation that most would have <20% RV pacing and would be randomized into INTRINSIC RV. Early analysis showed that targets for randomization were not met. AVSH parameters were modified under a protocol amendment to increase AV delay extension to 100%. We report findings related to this programming change based upon analyses of (nonrandomized) data pre- and post-amendment.
  
  
  RESULTS
  Twenty-one percent of patients (n = 314) were enrolled pre-amendment and 79% (n = 1,216) were enrolled post-amendment. The mean percentage of RV pacing at the 1-week visit was 41.4 +/- 29.6% pre-amendment and 14.7 +/- 22.6% post-amendment (P < 0.0001). The proportion of patients eligible for randomization (RV pacing <20% at the 1-week visit) was 31.2% pre-amendment and 76.8% post-amendment (P < 0.0001).
  
  
  CONCLUSIONS
  AVSH can dramatically reduce the percentage of RV pacing among ICD recipients.
authors.affiliation: University of Iowa Hospitals, Iowa City, Iowa 52242, USA. brian.olshansky@uiowa.edu
authors.forename: Brian
authors.initials: B
authors.lastname: Olshansky
authors.forename: John
authors.initials: J
authors.lastname: Day
authors.forename: Maureen
authors.initials: M
authors.lastname: McGuire
authors.forename: Stephen
authors.initials: S
authors.lastname: Hahn
authors.forename: Scott
authors.initials: S
authors.lastname: Brown
authors.forename: Darin R
authors.initials: DR
authors.lastname: Lerew
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable / Q000706:statistics & numerical data*; D005260:Female; D006333:Heart Failure / Q000401:mortality* / Q000517:prevention & control*; D006801:Humans; D008297:Male; D010138:Pacemaker, Artificial / Q000706:statistics & numerical data*; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D018497:Ventricular Dysfunction, Right / Q000401:mortality* / Q000517:prevention & control*; D014693:Ventricular Fibrillation / Q000401:mortality / Q000517:prevention & control