title: Cardiac resynchronization therapy in non-left bundle branch block morphologies.
abstract: BACKGROUND
  In select patients with systolic heart failure, cardiac resynchronization therapy (CRT) has been shown to improve quality of life, exercise capacity, ejection fraction (EF), and survival. Little is known about the response to CRT in patients with right bundle branch block (RBBB) or non-specific intraventricular conduction delay (IVCD) compared with traditionally studied patients with left bundle branch block (LBBB).
  
  
  METHODS
  We assessed 542 consecutive patients presenting for the new implantation of a CRT device. Patients were placed into one of three groups based on the preimplantation electrocardiogram morphology: LBBB, RBBB, or IVCD. Patients with a narrow QRS or paced ventricular rhythm were excluded. The primary endpoint was long-term survival. Secondary endpoints were changes in EF, left ventricular end-diastolic and systolic diameter, mitral regurgitation, and New York Heart Association (NYHA) functional class.
  
  
  RESULTS
  Three hundred and thirty-five patients met inclusion criteria of which 204 had LBBB, 38 RBBB, and 93 IVCD. There were 32 deaths in the LBBB group, 10 in the RBBB, and 27 in the IVCD group over a mean follow up of 3.4 +/- 1.2 years. In multivariate analysis, no mortality difference amongst the three groups was noted. Patients with LBBB had greater improvements in most echocardiographic endpoints and NYHA functional class than those with IVCD and RBBB.
  
  
  CONCLUSIONS
  There is no difference in 3-year survival in patients undergoing CRT based on baseline native QRS morphology. Patients with RBBB and IVCD derive less reverse cardiac remodeling and symptomatic benefit from CRT compared with those with a native LBBB.
authors.affiliation: Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, Ohio 44195, USA. rickarj2@ccf.org
authors.forename: John
authors.initials: J
authors.lastname: Rickard
authors.forename: Dharam J
authors.initials: DJ
authors.lastname: Kumbhani
authors.forename: Eiran Z
authors.initials: EZ
authors.lastname: Gorodeski
authors.forename: Bryan
authors.initials: B
authors.lastname: Baranowski
authors.forename: Oussama
authors.initials: O
authors.lastname: Wazni
authors.forename: David O
authors.initials: DO
authors.lastname: Martin
authors.forename: Richard
authors.initials: R
authors.lastname: Grimm
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Wilkoff
mesh_terms: D000368:Aged; D002037:Bundle-Branch Block / Q000000981:diagnostic imaging / Q000401:mortality / Q000628:therapy*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D015331:Cohort Studies; D005260:Female; D054143:Heart Failure, Systolic / Q000000981:diagnostic imaging / Q000401:mortality / Q000628:therapy*; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial; D012189:Retrospective Studies; D016896:Treatment Outcome; D014463:Ultrasonography