title: Cardiac resynchronization therapy improves heart rate variability in patients with symptomatic heart failure.
abstract: BACKGROUND
  Cardiac resynchronization therapy (CRT) using biventricular pacing improves symptoms and functional capacity in patients with moderate to severe heart failure. The present study examined whether an improvement in ventricular performance from resynchronization therapy changes the autonomic control of heart rate.
  
  
  RESULTS
  Heart rate variability (HRV) was examined in 50 patients implanted with the InSync biventricular pacing system who were randomized to therapy-on (n=25) or therapy-off (n=25). HRV was computed as the standard deviation of the atrial cycle length sensed from the system over 2 months of continuous monitoring. HRV was compared between CRT-on and CRT-off groups. HRV was higher in patients randomized to CRT-on compared with CRT-off (148+/-47 ms for CRT-on versus 118+/-45 ms for CRT-off; P=0.02), despite the lack of difference in mean atrial cycle length (844+/-129 ms for CRT-on versus 851+/-110 ms for CRT-off; P=0.82). Changes in plasma catecholamines were not different between the CRT-on and CRT-off groups from baseline to the 3-month follow-up.
  
  
  CONCLUSIONS
  Improvement in ventricular performance from CRT shifts cardiac autonomic balance toward a more favorable profile that is less dependent on sympathetic activation.
authors.affiliation: Department of Internal Medicine, Cardiovascular Disease Section, University of Oklahoma Health Sciences Center, PO Box 26901, 920 SL Young Boulevard, WP3120, Oklahoma City, Okla 73104, USA. philip-adamson@OUHSC.edu
authors.forename: Philip B
authors.initials: PB
authors.lastname: Adamson
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Kleckner
authors.forename: Warren L
authors.initials: WL
authors.lastname: VanHout
authors.forename: Sriram
authors.initials: S
authors.lastname: Srinivasan
authors.forename: William T
authors.initials: WT
authors.lastname: Abraham
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D002395:Catecholamines / Q000097:blood; D017147:Defibrillators, Implantable; D004452:Echocardiography; D015716:Electrocardiography, Ambulatory; D005260:Female; D005500:Follow-Up Studies; D006325:Heart Atria / Q000000981:diagnostic imaging / Q000503:physiopathology; D006333:Heart Failure / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial; D013564:Sympathetic Nervous System / Q000503:physiopathology; D016896:Treatment Outcome; D018754:Ventricular Dysfunction / Q000503:physiopathology / Q000628:therapy
chemical_list: D000319:Adrenergic beta-Antagonists; D002395:Catecholamines