title: Adverse effect of ventricular pacing on heart failure and atrial fibrillation among patients with normal baseline QRS duration in a clinical trial of pacemaker therapy for sinus node dysfunction.
abstract: BACKGROUND
  Dual-chamber (DDDR) pacing preserves AV synchrony and may reduce heart failure (HF) and atrial fibrillation (AF) compared with ventricular (VVIR) pacing in sinus node dysfunction (SND). However, DDDR pacing often results in prolonged QRS durations (QRSd) as the result of right ventricular stimulation, and ventricular desynchronization may result. The effect of pacing-induced ventricular desynchronization in patients with normal baseline QRSd is unknown.
  
  
  RESULTS
  Baseline QRSd was obtained from 12-lead ECGs before pacemaker implantation in MOST, a 2010-patient, 6-year, randomized trial of DDDR versus VVIR pacing in SND. Cumulative percent ventricular paced (Cum%VP) was determined from stored pacemaker data. Baseline QRSd <120 ms was observed in 1339 patients (707 DDDR, 632 VVIR). Cum%VP was greater in DDDR versus VVIR (90% versus 58%, P=0.001). Cox models demonstrated that the time-dependent covariate Cum%VP was a strong predictor of HF hospitalization in DDDR (hazard ratio [HR], 2.99 [95% CI, 1.15 to 7.75] for Cum%VP >40%) and VVIR (HR 2.56 [95% CI, 1.48 to 4.43] for Cum%VP >80%). The risk of AF increased linearly with Cum%VP from 0% to 85% in both groups (DDDR, HR 1.36 [95% CI, 1.09, 1.69]; VVIR, HR 1.21 [95% CI 1.02, 1.43], for each 25% increase in Cum%VP). Model results were unaffected by adjustment for known baseline predictors of HF hospitalization and AF.
  
  
  CONCLUSIONS
  Ventricular desynchronization imposed by ventricular pacing even when AV synchrony is preserved increases the risk of HF hospitalization and AF in SND with normal baseline QRSd.
authors.affiliation: Cardiac Arrhythmia Service, Brigham and Women's Hospital and Harvard Medical School, 75 Francis St, Boston, Mass 02115, USA. mosweeney@partners.org
authors.forename: Michael O
authors.initials: MO
authors.lastname: Sweeney
authors.forename: Anne S
authors.initials: AS
authors.lastname: Hellkamp
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Ellenbogen
authors.forename: Arnold J
authors.initials: AJ
authors.lastname: Greenspon
authors.forename: Roger A
authors.initials: RA
authors.lastname: Freedman
authors.forename: Kerry L
authors.initials: KL
authors.lastname: Lee
authors.forename: Gervasio A
authors.initials: GA
authors.lastname: Lamas
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000209:etiology*; D001919:Bradycardia / Q000150:complications / Q000628:therapy; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects* / Q000379:methods; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006333:Heart Failure / Q000209:etiology*; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D016016:Proportional Hazards Models; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data; D018570:Risk Assessment; D012804:Sick Sinus Syndrome / Q000150:complications / Q000175:diagnosis / Q000628:therapy*; D016019:Survival Analysis