title: Stimulus intensity in left ventricular leads and response to cardiac resynchronization therapy.
abstract: BACKGROUND
  Increased left ventricular (LV) stimulus intensity has been shown to improve conduction velocity and cardiac output. However, high-output pacing would shorten device battery life. Our prospective trial analyzed the clinical effects of high- versus low-output LV pacing.
  
  
  RESULTS
  Thirty-nine patients undergoing initial cardiac resynchronization therapy device implantation with bipolar LV leads were assigned to 3 months of either high-output LV pacing (Hi) or low-output LV pacing (Lo) in a randomized, blinded crossover fashion. Hi and Lo settings were determined with a rigorous intraoperative protocol specific to each patient. Clinical and echocardiographic data were obtained at randomization, at 3 months, and a subsequent 3 months after crossover. Mean age was 66.4±9.8 years, and mean QRS duration was 159.3±23.1 ms. Compared to baseline, both arms had significant improvements in Minnesota Living With Heart Failure score (given as mean [95% confidence interval]) (baseline versus Lo: 43.3 [35.5 to 51.1] versus 21.3 [14.6 to 28.0], P<0.01; baseline versus Hi: 43.3 [35.5 to 51.1] versus 23.6 [16.1 to 31.1], P<0.01) and 6-minute walk distance (baseline versus Lo: 692 ft [581 to 804] versus 995 ft [876 to 1114], P<0.01; baseline versus Hi: 699 ft [585 to 813] versus 982 ft [857 to 1106], P<0.01). Although both Hi and Lo arms had some echocardiographic parameters that significantly improved compared to baseline (baseline end-diastolic diameter 5.7 cm [5.5 to 6.0] versus Lo 5.5 cm [5.1 to 5.8], P<0.01; baseline end-systolic diameter 4.9 cm [4.6 to 5.3] versus Hi 4.7 cm [4.3 to 5.0], P<0.05), there were no significant differences observed when comparing the Hi- versus Lo-output arms.
  
  
  CONCLUSIONS
  Low-output LV pacing with a relatively narrow safety margin above capture threshold affords significant improvement from baseline and is clinically equivalent to high-output LV pacing. These data support a strategy of minimizing the programmed LV safety margin to increase battery life in cardiac resynchronization therapy devices.
  
  
  BACKGROUND
  URL: http://www.clinicaltrials.gov. Unique identifier: NCT01060449.
authors: Emory University School of Medicine, Atlanta, GA 30322, USA.
authors: Venkata V
authors: VV
authors: Bavikati
authors: Jonathan J
authors: JJ
authors: Langberg
authors: B Robinson
authors: BR
authors: Williams
authors: Danesh
authors: D
authors: Kella
authors: Michael S
authors: MS
authors: Lloyd
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004452:Echocardiography; D004562:Electrocardiography; D005260:Female; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011795:Surveys and Questionnaires; D016896:Treatment Outcome
keywords: cardiac resynchronization; congestive heart failure; pacing