title: Cardiac resynchronization therapy in patients with heart failure and conduction abnormalities other than left bundle-branch block: analysis of the Multicenter InSync Randomized Clinical Evaluation (MIRACLE).
abstract: BACKGROUND
  Cardiac resynchronization therapy (CRT) has been proposed as a treatment for patients with congestive heart failure (CHF) and prolonged QRS durations. Previous studies have predominantly included patients with left bundle-branch block (LBBB). The Multicenter InSync Randomized Clinical Evaluation (MIRACLE) investigators assessed the efficacy of CRT in patients with CHF with QRS durations > or = 130 ms and found that CRT lead to improvement in several measures of functional capacity and exercise tolerance.
  
  
  OBJECTIVE
  We designed this retrospective study to determine whether patients with CHF who have conduction abnormalities other than LBBB also respond favorably to CRT.
  
  
  METHODS
  We divided patients enrolled in the MIRACLE trial into three subgroups according to conduction abnormality--LBBB, right bundle-branch block (RBBB), and nonspecific interventricular conduction delay (IVCD)--and compared the response among and within these groups to CRT or no CRT at baseline and 6-months' follow-up.
  
  
  RESULTS
  We found 313 patients with LBBB, 43 with RBBB, and 35 with IVCD. When they received CRT, significant improvement was achieved in functional class (p = 0.001) by patients with RBBB, and in quality of life (p = 0.038) by patients with IVCD. Patients in the RBBB and IVCD groups showed improvement in exercise time and peak oxygen consumption after CRT. Most patients with RBBB (82%) also had either left anterior fascicular block or left posterior fascicular block.
  
  
  CONCLUSIONS
  Patients with CHF with RBBB and IVCD do benefit from CRT. Improvement with CRT in patients with RBBB may be due to concomitant left-sided conduction abnormalities. Further subgroup analyses of other CRT trials are necessary to validate these results.
authors.affiliation: University of Florida College of Medicine, Gainesville, Florida 32610, USA. arandjm@mail-cs.med.ufl.edu
authors.forename: Juan M
authors.initials: JM
authors.lastname: Aranda
authors.forename: Jamie B
authors.initials: JB
authors.lastname: Conti
authors.forename: James W
authors.initials: JW
authors.lastname: Johnson
authors.forename: Susan
authors.initials: S
authors.lastname: Petersen-Stejskal
authors.forename: Anne B
authors.initials: AB
authors.lastname: Curtis
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D002036:Bundle of His / Q000503:physiopathology*; D002037:Bundle-Branch Block / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006333:Heart Failure / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015337:Multicenter Studies as Topic; D016032:Randomized Controlled Trials as Topic; D012189:Retrospective Studies; D016896:Treatment Outcome