A SIMULTANEOUS, NONINVASIVE COMPARISON WITH SINUS RHYTHM, OF 2 ACTIVITY SENSING, RATE ADAPTIVE PACEMAKERS, IN AN ELDERLY POPULATION

We compared the rate response to low level work, arm exercise, step testing, and treadmill exercise between the Siemens Sensolog 703 S (Sg) and the Medtronic Activitrax (Ax) pacemakers, and simultaneous sinus rhythm (SR) in an elderly population. In ten subjects mean age 70.6 years, range 49-81 years, the pacemaker responses were noninvasively compared by strapping the units to the chest wall under constant and equal pressure applied by an adjustable belt. Pacemaker rates and SR were recorded simultaneously on a three-channel ECG recorder. The units were programmed in situ to give an increase in rate from 70 beats/min sitting, to 100 beats/min after walking at a normal pace for 30 seconds. Programming took three times longer for Sg (P < 0.02). The response to standing and bending was poor for both units (Ax mean 75.5 beats/min, Sg mean 77.6 beats/min), when compared to SR (mean 90.3 beats/min). A 20-step test resulted in a greater rate response from Ax (mean 105.3 beats/min) than from Sg (mean 96.3 beats/min [P = 0.09]), though both were still less than SR (116.3). There were significant differences between the two pacemakers on treadmill testing, at peak rate achieved (Ax mean 116.5 beats/min; Sg mean 102.7 beats/min [P < 0.005], SR mean 122.5 beats/min) and at end exercise (Ax mean 112.5 beats/min; Sg mean 92.9 beats/min [P < 0.002], SR mean 121.3 beats/min). Arm exercise, however, resulted in a significantly greater response from Sg than Ax (105.1 and 88.5 beats/min, respectively; P < 0.01, SR 98.7 beats/min). For each pacemaker the entire battery of 19 observations (7 exercise parameters and 12 treadmill timepoints) were analyzed to assess the correlation with SR; Ax was found to correlate very closely with SR (r = 0.94, P < 0.0001), while Sg had a poor correlation with SR (r = 0.40, P < 0.09). In conclusion, Ax was quicker to program and had a much better correlation to SR than did Sg, when programmed as described in the elderly population. Both pacemakers responded poorly to changes in posture, and gave a lower rate response than SR for almost all exercises.