title: Cardiac-resynchronization therapy in heart failure with narrow QRS complexes.
abstract: BACKGROUND
  Indications for cardiac-resynchronization therapy (CRT) in patients with heart failure include a prolonged QRS interval (> or =120 msec), in addition to other functional criteria. Some patients with narrow QRS complexes have echocardiographic evidence of left ventricular mechanical dyssynchrony and may also benefit from CRT.
  
  
  METHODS
  We enrolled 172 patients who had a standard indication for an implantable cardioverter-defibrillator. Patients received the CRT device and were randomly assigned to the CRT group or to a control group (no CRT) for 6 months. The primary end point was the proportion of patients with an increase in peak oxygen consumption of at least 1.0 ml per kilogram of body weight per minute during cardiopulmonary exercise testing at 6 months.
  
  
  RESULTS
  At 6 months, the CRT group and the control group did not differ significantly in the proportion of patients with the primary end point (46% and 41%, respectively). In a prespecified subgroup with a QRS interval of 120 msec or more, the peak oxygen consumption increased in the CRT group (P=0.02), but it was unchanged in a subgroup with a QRS interval of less than 120 msec (P=0.45). There were 24 heart-failure events requiring intravenous therapy in 14 patients in the CRT group (16.1%) and 41 events in 19 patients in the control group (22.3%), but the difference was not significant.
  
  
  CONCLUSIONS
  CRT did not improve peak oxygen consumption in patients with moderate-to-severe heart failure, providing evidence that patients with heart failure and narrow QRS intervals may not benefit from CRT. (ClinicalTrials.gov number, NCT00132977 [ClinicalTrials.gov].).
authors.affiliation: University of Chicago, Chicago, USA. jbeshai@medicine.bsd.uchicago.edu
authors.forename: John F
authors.initials: JF
authors.lastname: Beshai
authors.forename: Richard A
authors.initials: RA
authors.lastname: Grimm
authors.forename: Sherif F
authors.initials: SF
authors.lastname: Nagueh
authors.forename: James H
authors.initials: JH
authors.lastname: Baker
authors.forename: Scott L
authors.initials: SL
authors.lastname: Beau
authors.forename: Steven M
authors.initials: SM
authors.lastname: Greenberg
authors.forename: Luis A
authors.initials: LA
authors.lastname: Pires
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Tchou
mesh_terms: D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000628:therapy*; D002304:Cardiac Pacing, Artificial; D018592:Cross-Over Studies; D017147:Defibrillators, Implantable / Q000009:adverse effects; D004562:Electrocardiography; D005260:Female; D006333:Heart Failure / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011788:Quality of Life; D017211:Treatment Failure