title: Intrinsic heart rate response as a predictor of rate-adaptive pacing benefit.
abstract: OBJECTIVE
  More than half of the pacemaker systems now being implanted can be rate adaptively paced. Our objective was to determine which patients benefit from rate-adaptive pacing in terms of improvement in maximum performance and aerobic capacity.
  
  
  METHODS
  Thirty patients with implanted accelerometer-driven, rate-adaptive pacemakers underwent a standardized, ergospirometrically and maximally symptoms = limited cardiopulmonary exercise (CPX) stress test with both rate-adaptive and fixed-rate stimulation in a randomized order. The patients were divided into three groups depending on the intrinsic heart rate achieved during maximum workload: group 1 achieved < or = 90 beats per minute (bpm), group 2 achieved 90 to < or = 110 bpm, and group 3 achieved > 110 bpm.
  
  
  RESULTS
  Group 1 demonstrated a significant increase (p < or = 0.01) in maximum oxygen uptake from 16.4 +/- 5.6 mL/kg/min with fixed-rate pacing to 23.2 +/- 11.1 mL/kg/min (+ 41.5%) with rate-adaptive pacing. At the anaerobic threshold, oxygen uptake significantly increased (p < or = 0.01) from 11.8 +/- 2.7 mL/kg/min to 15.7 +/- 5 mL/kg/min (+33.1%). Group 2 patients showed an increase in maximum oxygen uptake from 23.3 +/- 5.4 mL/kg/min to 25.3 +/- 4.9 mL/kg/min (+8.5%, p < or = 0.05) as well as an increase in oxygen uptake at the anaerobic threshold from 15.9 +/- 2.6 mL/kg/min to 18.1 +/- 2.9 mL/kg/min (+13.8%, p < or = 0.05) with rate-adaptive pacing. Group 3 demonstrated no significant difference between the two pacing methods (from 25.6 +/- 9.4 mL/kg/min to 25.9 +/- 9.3 mL/kg/min and from 15.8 +/- 5.5 mL/kg/min to 16.3 +/- 6 mL/kg/min). No difference in maximum oxygen uptake and in oxygen uptake at the anaerobic threshold was evident among the three groups when paced rate adaptively (not significant).
  
  
  CONCLUSIONS
  The second-generation, accelerometer controlled rate-adaptive pacemakers used in testing enabled a stress-oriented heart rate increase and an age- and gender-dependent adequate matching of maximum performance. The benefit from a rate-adaptive system to the patient increases as his or her chronotropic reserve limitation became more pronounced.
authors.affiliation: 1. Medizinische Klinik, Technische Universität München, Germany.
authors.forename: E U
authors.initials: EU
authors.lastname: Alt
authors.forename: M J
authors.initials: MJ
authors.lastname: Schlegl
authors.forename: M M
authors.initials: MM
authors.lastname: Matula
mesh_terms: D000367:Age Factors; D015308:Anaerobic Threshold; D002304:Cardiac Pacing, Artificial / Q000379:methods; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D012737:Sex Factors