ACTIVITY-BASED PACING - COMPARISON OF A DEVICE USING AN ACCELEROMETER VERSUS A PIEZOELECTRIC CRYSTAL

The EXCEL(TM) VR, an accelerometer-based pacemaker (AC), and the Legend(TM), a pacemaker utilizing a piezoelectric crystal (PZ), were compared under ergometric conditions and during stair climbing to assess the appropriateness of their rate responses. The pacemakers, programmed to the manufacturers' nominal settings in order to compare different technologically based sensors under identical conditions, were strapped over subjects' left mid-pectoral region. Placement of the devices was randomized to control for positional effects. Ten healthy subjects (55-72 years) completed a graded exercise treadmill test to 80% of maximum predicted heart rate (HR). An additional group of ten subjects (50-66 years) completed exercise protocols involving bicycle ergometry and stair climbing. Throughout all tests, pacemaker pulse rates and subjects' intrinsic HR were monitored continuously. For the treadmill exercise, the average correlations between the AC and PZ pacemakers' pulse rate and HR for the group as a whole were r = 0.92 and r = 0.82, respectively. Individual subject comparisons were also made between each pacemaker rate and intrinsic HR. The mean difference from intrinsic rate was 11 ppm for the AC pacemaker and 24 ppm for the PZ pacemaker. In addition, the PZ pacemaker's maximal pulse rate was significantly lower (105 +/- 9.6 ppm) than the other two rates (AC 137 +/- 6 ppm; intrinsic HR 129 +/- 2 beats/min). Throughout the bicycle ergometry testing, the intrinsic HR was higher than the AC and PZ pacing rates. However, the AC's rate was significantly higher than the PZ's rate. When subjects ascended stairs, the intrinsic HR and AC rate were closely correlated, but the PZ rate was significantly lower. When subjects descended stairs, neither pacemaker's rate matched intrinsic HR. These results indicate that the AC pacemaker more closely matches intrinsic HR in healthy subjects during ergometric activity and stair climbing than does the PZ pacemaker. Although the three activities evaluated in this study may be lacking representation of other common daily tasks, these results do lend support for considering the use of an AC pacemaker. These data also suggest the need for further research using activity-based rate-responsive pacemakers after parameter optimization for each subject to address issues of sensitivity to and specificity of human movement.