title: The incremental benefit of rate-adaptive pacing on exercise performance during cardiac resynchronization therapy.
abstract: OBJECTIVE
  The purpose of this research was to investigate the effect of using rate-adaptive pacing and atrioventricular interval (AVI) adaptation on exercise performance during cardiac resynchronization therapy (CRT).
  
  
  BACKGROUND
  The potential incremental benefits of using rate-adaptive pacing and AVI adaptation with CRT during exercise have not been studied.
  
  
  METHODS
  We studied 20 patients with heart failure, chronotropic incompetence (<85% age-predicted heart rate [AP-HR] and <80% HR reserve), and implanted with CRT. All patients underwent a cardiopulmonary exercise treadmill test using DDD mode with fixed AVI (DDD-OFF), DDD mode with adaptive AVI on (DDD-ON), and DDDR mode with adaptive AVI on (DDDR-ON) to measure metabolic equivalents (METs) and peak oxygen consumption (VO2max).
  
  
  RESULTS
  During DDD-OFF mode, not all patients reached 85% AP-HR during exercise, and 55% of patients had <70% AP-HR. Compared to patients with >70% AP-HR, patients with <70% AP-HR had significantly lower baseline HR (66 +/- 3 beats/min vs. 80 +/- 5 beats/min, p = 0.015) and percentage HR reserve (27 +/- 5% vs. 48 +/- 6%, p = 0.006). In patients with <70% AP-HR, DDDR-ON mode increased peak exercise HR, exercise time, METs, and VO2max compared with DDD-OFF and DDD-ON modes (p < 0.05), without a significant difference between DDD-OFF and DDD-ON modes. In contrast, there were no significant differences in peak exercise HR, exercise time, METs, and VO2max among the three pacing modes in patients with >70% AP-HR. The percentage HR changes during exercise positively correlated with exercise time (r = 0.67, p < 0.001), METs (r = 0.56, p < 0.001), and VO2max (r = 0.55, p < 0.001).
  
  
  CONCLUSIONS
  In heart failure patients with severe chronotropic incompetence as defined by failure to achieve >70% AP-HR, appropriate use of rate-adaptive pacing with CRT provides incremental benefit on exercise capacity during exercise.
authors.affiliation: Cardiology Division, Department of Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong, China.
authors.forename: Hung-Fat
authors.initials: HF
authors.lastname: Tse
authors.forename: Chung-Wah
authors.initials: CW
authors.lastname: Siu
authors.forename: Kathy L F
authors.initials: KL
authors.lastname: Lee
authors.forename: Katherine
authors.initials: K
authors.lastname: Fan
authors.forename: Hon-Wah
authors.initials: HW
authors.lastname: Chan
authors.forename: Man-Oi
authors.initials: MO
authors.lastname: Tang
authors.forename: Vella
authors.initials: V
authors.lastname: Tsang
authors.forename: Stephen W L
authors.initials: SW
authors.lastname: Lee
authors.forename: Chu-Pak
authors.initials: CP
authors.lastname: Lau
mesh_terms: D000222:Adaptation, Physiological; D000368:Aged; D000465:Algorithms; D001283:Atrioventricular Node / Q000503:physiopathology; D002303:Cardiac Output, Low / Q000503:physiopathology* / Q000628:therapy*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D015444:Exercise; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index