[The effect of step rate and muscle force on the rate response of activity-modulated cardiac pacemaker]

Programming of activity-modulated pacemakers allows an individual adaptation of rate response. In 26 pacemaker patients (Activitrax n = 16; Synergyst n = 10; Medtronic) it was tested whether rate-response parameters can already be programmed under consideration of patient's characteristics. At a fixed rate-response setting (VVIR/VOOR mode, pacing rate range: 60-130 ppm, MEDIUM/7) four treadmill exercise tests were performed: three step-rate controlled tests with 40, 80, and 120 steps/min and a symptom-limited exercise test with 1 km/h initial speed and 1 km/h speed increments every second minute. Maximal pacing rates at 80 steps/min (72 +/- 14 ppm) and 120 steps/min (90 +/- 6 ppm) were higher than at 40 steps/min (63 +/- 6 ppm). Forced steps with a step rate of 40/min resulted in a higher pacing rate compared to normal steps. At symptom-limited exercise, maximum pacing rates increased to 102 +/- 19 ppm with a range from 60 ppm to 124 ppm. Positive correlations were found between maximum step rate and maximum pacing rate (r = 0.55), between exercise duration and maximum pacing rate (r = 0.70), and between exercise duration and maximum step rate (r = 0.78). Patients with an exercise tolerance up to 5 km/h achieved pacing rates from 91 and 124 ppm, but patients with restricted exercise tolerance had lower maximum pacing rates due to their lower maximum step frequencies. Step rate and body force are important movements in the generation of body vibrations.