Effects of body constitution and age on maximum pacing rate of activity-modulated rate responsive pacemakers

The pacing rate of activity-modulated pacemakers is triggered by vibrations running through the body. Whether the body constitution predicts maximum pacing rate and may facilitate rate response programming was studied in 16 patients with Activitrax pacemakers. Rate response parameters were programmed to a fixed setting in VVIR/VOOR mode (lower pacing rate 60 ppm, upper pacing rate 125-130 ppm, activity threshold medium/7). Body vibrations were induced by a treadmill exercise test with increasing speed. Maximum pacing rates were measured at the stage of symptom-limited tolerance. Exercise tests with a duration of 7.3 +/- 2.9 minutes resulted in a maximum pacing rate of 98 +/- 22 ppm ranging from 60-122 ppm. Maximum pacing rates did not differ between male (n = 10; 102 +/- 21 ppm) and female (n = 6; 92 +/- 24 ppm). Correlations between maximum pacing rates and body constitutional factors were not significant with r = -0.15 (weight), r = 0.39 (height), r = 0.07 (body surface area), and r = -0.27 (skin-fold thickness). The correlations with body mass index (r = -0.53) and age (r = -0.53) were initially significant, but not after Bonferroni-Simes-Hommel correction. The age-dependent relationship may be caused by the shorter exercise duration of older patients indicated by the correlation between exercise duration and maximum pacing rate (r = 0.77), as well as with age (r = -0.73).

body constitution did not modify body vibrations and did not allow prediction of maximum pacing rates; therefore, it is no aid for the programming of rate response parameters.