title: QRS narrowing is associated with reverse remodeling in patients with chronic right ventricular pacing upgraded to cardiac resynchronization therapy.
abstract: BACKGROUND
  Patients with chronic right ventricular pacing (RVP) upgraded to cardiac resynchronization therapy (CRT) have been excluded from the majority of clinical trials of CRT. Little is known about the predictors of response in this population. We hypothesized that reversal of RVP-induced electrical dyssynchrony (indexed by QRS duration) by CRT would predict a favorable response.
  
  
  OBJECTIVE
  The purpose of this study was to identify baseline characteristics associated with response in patients upgraded to CRT from chronic RVP.
  
  
  METHODS
  Consecutive patients presenting for CRT at the Cleveland Clinic between September 30, 2003, and July 8, 2008, with chronic RVP and serial echocardiograms were included in this analysis. RVP was defined as>85% pacing on a pre-CRT device check, previous AV nodal ablation, or complete pacer dependency per chart notes. Response was defined as a reduction in left ventricular end-systolic volume ≥ 15% from baseline. Clinical, ECG, and echocardiographic data were extracted to determine covariates associated with response.
  
  
  RESULTS
  One hundred twelve patients met inclusion criteria, of whom 72 (64.3%) met criteria for response over median follow-up of 9.9 months (interquartile range [6.5-14.7]). No significant differences were noted in terms of male gender (68.1% vs 75.0%; P = .52), ischemic cardiomyopathy (55.6% vs 55.0%; P = 1), pre-CRT QRS duration (189.1 ± 20.7 ms vs 185.5 ± 26.8 ms; P = .47), duration of RVP before CRT upgrade (5.8 ± 3.9 years vs 6.2 ± 4.0 years; P = .57), or baseline left ventricular end-systolic volume (160.0 ± 60.7 mL vs 172.8 ± 67.2 mL; P = .32) between responders and nonresponders, respectively. Percent reduction in QRS duration between the right ventricular-paced and first biventricular-paced waveforms was significantly greater in responders compared with nonresponders (14.4% ± 13.2% vs 7.2%± 14.0%; P = .01). In multivariate analysis, percent reduction in QRS narrowing was the lone factor associated with response (odds ratio 0.02 [0.001-0.42]; P = .01).
  
  
  CONCLUSIONS
  Reversal of electrical dyssynchrony predicts response to CRT in chronically RV-paced patients upgraded to CRT. Traditional factors associated with a favorable response to CRT in de novo implants (female gender, nonischemic cardiomyopathy, and wider baseline QRS duration) are not significantly associated with response in upgraded patients. Duration of RVP before CRT upgrade is not an important determinant of response.
authors.affiliation: Heart and Vascular Institute Cleveland Clinic, Cleveland, Ohio 44122, USA. jricar5@exchange.johnshopkins.edu
authors.forename: John
authors.initials: J
authors.lastname: Rickard
authors.forename: Alan
authors.initials: A
authors.lastname: Cheng
authors.forename: David
authors.initials: D
authors.lastname: Spragg
authors.forename: Daniel
authors.initials: D
authors.lastname: Cantillon
authors.forename: Mina K
authors.initials: MK
authors.lastname: Chung
authors.forename: W H Wilson
authors.initials: WH
authors.lastname: Tang
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Wilkoff
authors.forename: Niraj
authors.initials: N
authors.lastname: Varma
mesh_terms: D000368:Aged; D001145:Arrhythmias, Cardiac / Q000503:physiopathology* / Q000628:therapy; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D004452:Echocardiography; D004562:Electrocardiography; D005260:Female; D006333:Heart Failure / Q000503:physiopathology* / Q000628:therapy; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D016896:Treatment Outcome; D020257:Ventricular Remodeling / Q000502:physiology*