title: Upgrade and de novo cardiac resynchronization therapy: impact of paced or intrinsic QRS morphology on outcomes and survival.
abstract: BACKGROUND
  Cardiac resynchronization therapy (CRT) improves outcomes in patients with left bundle branch block (LBBB), but the benefits of CRT in patients with other QRS morphologies or previous pacing are uncertain.
  
  
  OBJECTIVE
  The purpose of this study was to describe outcomes in patients with prior right ventricular pacing and non-LBBB morphologies.
  
  
  METHODS
  We studied 505 patients who underwent de novo CRT (n = 338) or CRT upgrade (n = 167). De novo patients were categorized by underlying QRS morphology: LBBB (67%), right bundle branch block (RBBB; 11%), intraventricular conduction delay (IVCD; 13%), and QRS <120 ms (9%). Upgrade patients were categorized by the percentage of previous ventricular pacing.
  
  
  RESULTS
  Patients were followed for death over a median of 2.6 years (interquartile range 1.6-4.0). New York Heart Association (NYHA) functional class and echocardiographic improvements were similar in de novo and upgrade patients. However, within the de novo group, NYHA improvements were less in patients with RBBB (0.3 +/- 0.8; P = .014) or IVCD (0.2 +/- 0.7; P = .001) than in those with LBBB (0.7 +/- 0.8). These patients had less left ventricular functional improvement as well. Survival was comparable after de novo versus upgrade CRT (61% vs 63% at 4 years; P = .906). No clinical or survival differences were noted in upgrade patients based on the percentage of previous pacing. However, survival in de novo CRT recipients with RBBB (32%) was lower than in those with LBBB (66%; P <.001), and RBBB independently predicted death (hazard ratio 3.5, confidence interval 1.9-6.5; P <.001).
  
  
  CONCLUSIONS
  RBBB and IVCD result in less clinical improvement or worsened survival after CRT. Additional selection criteria may be beneficial in identifying potential responders with RBBB, IVCD, or narrow QRS.
authors.affiliation: Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Anita
authors.initials: A
authors.lastname: Wokhlu
authors.forename: Robert F
authors.initials: RF
authors.lastname: Rea
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Asirvatham
authors.forename: Tracy
authors.initials: T
authors.lastname: Webster
authors.forename: Kelly
authors.initials: K
authors.lastname: Brooke
authors.forename: David O
authors.initials: DO
authors.lastname: Hodge
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Wiste
authors.forename: Yingxue
authors.initials: Y
authors.lastname: Dong
authors.forename: David L
authors.initials: DL
authors.lastname: Hayes
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Cha
mesh_terms: D000368:Aged; D001145:Arrhythmias, Cardiac / Q000401:mortality / Q000503:physiopathology*; D002037:Bundle-Branch Block / Q000401:mortality / Q000628:therapy; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006329:Heart Conduction System; D006333:Heart Failure / Q000503:physiopathology; D006801:Humans; D008297:Male; D011379:Prognosis; D016896:Treatment Outcome