Physical movement sensitive pacing: comparison of two "activity"-triggered pacing systems.

The Activitrax (A) and the Sensolog (S) pulse generator units were compared during bench tests and in patients both under ergometric conditions and during daily activities to determine the susceptibility of both systems to external noise. During the bench tests both pacemakers were mounted on a swingboard and subjected to controlled vibrational force. The patients were divided into two groups of 10 patients each, one group with A and the other with S units; the discriminating power of workload changes was examined under treadmill exercise. In six patients of each group the rate behavior of S and A during daily activities was recorded by Holter monitoring. During bench tests, S and A displayed a frequency-selective mode of operation between 2-70 Hz with the greatest sensitivity between 10-50 Hz. In patients, S showed a significantly higher discriminating power to changes in workload during treadmill exercise. According to y = 0.27x + 85.8 (r = 0.92) the relationship between the power and the pacing rate of S was linear, whereas with y = 0.04x + 89.8 (r = 0.2) the pacing rate of A was almost independent of the given power. The susceptibility to external noise occurring while riding in an auto, streetcar or train with rate increases between 7 ppm and 12 ppm did not significantly differ in both systems. Lying prone on the pacemakers produced brief (less than 1 min) rate increases of 38 ppm (S) and 18 ppm (A), respectively.