First Clinical Results With a New Temperature-Controlled Rate-Responsive Pacemaker

We examined the cardiopulmonary effects of maximum bicycle ergometer exercise in seven patients with implanted Intermedics Nova MR pacemakers for three types of pacing in a randomized sequence: VVI or AAI at 70 beats/min (SSI 70), rate-adaptive temperature-controlled pacing with the implanted Nova MR, and rate-adaptive activity-controlled pacing with a Medtronic Activitrax pacemaker taped to the chest wall, which triggered the implanted Nova MR in the VVT or AAT mode by skin electrodes. The maximum exercise tolerance was 67 W with SSI 70, 71 W with Activitrax pacing, and 91 W with Nova MR pacing; the maximum oxygen uptake was 17.6, 19.5, and 21.5 ml/min/kg, respectively. The highest heart rate achieved was 81 beats/min with SSI 70, 98 beats/min with the Activitrax, and 118 beats/min with the Nova MR on average; the mean rate increase from rest to maximum exercise was 11, 29, and 47 beats/min, respectively. With both rate-adaptive types of pacing (Nova MR and Activitrax), an increase in exercise tolerance and maximum heart rate could be achieved, but this increase was significantly more obvious with the temperature-controlled Nova MR than with the activity-controlled Activitrax. However, with a different form of exercise, for example, treadmill ergometry, the rate response of the Activitrax would presumably have been somewhat clearer.