title: Does cardiac resynchronization therapy provide unrecognized benefit in patients with prolonged PR intervals? The impact of restoring atrioventricular synchrony: an analysis from the COMPANION Trial.
abstract: BACKGROUND
  The influence of PR prolongation on outcomes after cardiac resynchronization therapy (CRT) is uncertain.
  
  
  OBJECTIVE
  To determine whether PR prolongation predicts outcomes in potential CRT candidates and whether CRT benefits these candidates regardless of baseline PR interval.
  
  
  METHODS
  A database of 1520 patients fulfilling criteria for CRT implant (the COMPANION Trial) was examined. Patients assigned to normal (PR < 200 ms) or prolonged (PR ≥ 200 ms) cohorts were compared within the optimal pharmacologic therapy (OPT) and CRT groups regarding an endpoint of all-cause mortality or heart failure hospitalization. CRT was compared with OPT in normal and prolonged PR interval groups. An interaction test was performed to determine whether CRT influenced outcome as a function of PR interval.
  
  
  RESULTS
  PR prolongation was present in 52% of COMPANION subjects. Randomization to CRT was associated with a reduction in the endpoint, but the strength of the association was greater for those with prolonged PR (hazard ratio = 0.54; P <.01) versus normal PR (hazard ratio = 0.71; P = .02) intervals. CRT (vs OPT) was associated with reduction in the endpoint for subjects with normal or prolonged PR intervals. Reduction in relative risk (CRT vs OPT) was 29% (P = .02) for those with normal PR intervals but was 46% (P <.01) for those with PR prolongation. No interaction was detected between PR interval cohort and treatment (P = .17).
  
  
  CONCLUSIONS
  PR prolongation may affect mortality and heart failure hospitalizations in patients with systolic dysfunction, heart failure, and wide QRS complexes. The effect of PR prolongation may be attenuated by CRT.
authors.affiliation: University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA. brian-olshansky@uiowa.edu
authors.forename: Brian
authors.initials: B
authors.lastname: Olshansky
authors.forename: John D
authors.initials: JD
authors.lastname: Day
authors.forename: Renee M
authors.initials: RM
authors.lastname: Sullivan
authors.forename: Patrick
authors.initials: P
authors.lastname: Yong
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Galle
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Steinberg
mesh_terms: D001145:Arrhythmias, Cardiac / Q000628:therapy*; D054537:Atrioventricular Block / Q000628:therapy*; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D009202:Cardiomyopathies / Q000401:mortality / Q000628:therapy*; D017147:Defibrillators, Implantable; D005260:Female; D006333:Heart Failure / Q000401:mortality*; D006760:Hospitalization; D006801:Humans; D008297:Male; D016019:Survival Analysis; D016896:Treatment Outcome