title: Effect of biventricular pacing on the exercise pathophysiology of heart failure.
abstract: BACKGROUND
  Biventricular pacing (BVP) is used for cardiac resynchronization therapy in wide-QRS-complex heart failure. We sought to quantify the effect of BVP on the exercise pathophysiology of heart failure patients.
  
  
  METHODS
  Using cardiopulmonary exercise testing, we analyzed exercise data for a multicenter study sponsored by St. Jude Medical. Patients had pacemaker electrodes implanted in both ventricles in the standard manner and were randomized by St. Jude before exercise testing. Exercise measurements included peak oxygen uptake (Vo(2)), peak O(2) pulse, anaerobic threshold (AT), and ventilatory equivalent for CO(2) (reflecting change in peak exercise cardiac output, stroke volume, maximal sustainable exercise capacity, and ventilation-perfusion mismatching, respectively) at baseline and at a 6-month follow-up. The studies included progressively and uniformly increasing work rate to maximum tolerance. The investigators were blinded both to sponsor-controlled randomization and pacemaker status. There were 239 paired 6-month studies, as follows: 47 studies served as the control with the pacemaker off (ie, the BVP-OFF group); and 192 patients received pacing (ie, the BVP-ON group).
  
  
  RESULTS
  The BVP-ON group significantly improved in all exercise parameters in contrast to the control group (p < 0.0001). When baseline measurements for the BVP-ON group were ranked in quintiles, only patients in the three functionally worst quintiles improved significantly at 6 months (peak Vo(2) < 11.6 mL/min/kg, AT < 7.6 mL/min/kg, peak O(2) pulse < 12.0 mL/beat, and minute ventilation/Vco(2) ratio at AT > 38.1) [p < 0.01 to < 0.0001].
  
  
  CONCLUSIONS
  BVP benefited aerobic function and ventilation-perfusion mismatching most in those patients with the greatest physiologic impairment.
authors.affiliation: Department of Medicine, Los Angeles Biomedical Research Institute at Harbor--UCLA Medical Center, 1124 W Carson St, Torrance, CA 90502, USA. kwasserman@labiomed.org
authors.forename: Karlman
authors.initials: K
authors.lastname: Wasserman
authors.forename: Xing-Guo
authors.initials: XG
authors.lastname: Sun
authors.forename: James E
authors.initials: JE
authors.lastname: Hansen
mesh_terms: D000368:Aged; D002303:Cardiac Output, Low / Q000503:physiopathology* / Q000628:therapy*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004311:Double-Blind Method; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D010138:Pacemaker, Artificial; D015656:Respiratory Mechanics; D013318:Stroke Volume / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology*