Rate response of temperature-based sensors in leadless pacemakers during exercise test: a small cohort study

Background Leadless pacemakers (LPs) rely on rate-responsive sensors for pacing during physical activity in patients with chronotropic incompetence or pacing-dependency. Previous studies evaluated the rate-responsiveness of motion-based sensors, used in tined-fixation LPs. However, for the temperature-based sensor (TBS), used in screw-fixation LPs, the existing literature is limited. Evaluating the performance of TBSs is clinically relevant to ensure appropriate heart rate (HR) adaptation during exercise. TBSs detect temperature changes in the central venous blood pool. An increase in temperature is interpreted as physical activity; the LP adjusts the pacing rate accordingly. Optimization of the TBS can be done by adjusting the gain setting or the maximum sensor rate (MSR). Objective The aim of this study is to assess the performance of the TBS during exercise in patients with a LP. Methods Patients with a screw-fixation LP and an activated TBS underwent an exercise test (ET) on a bicycle, where an ECG together with the performed workload (WL) was registered during the ET. Results Seven patients with a LP and activated TBS underwent an ET: four patients were implanted with a single atrial LP, two with a single ventricular LP, and one with a dual chamber LP. Six patients had a paced heart rhythm during the ET. Figure 1 illustrates the rate-responsive performance of the TBS in their LP. Pacemaker settings prior to the ET were nominal and not individually optimized except for patient 6, in whom settings were based on previous transvenous pacemaker parameters and a walking test. In 2 patients (#2, #3), 33%, a delayed sensor response was observed, with the highest HR occurring during the recovery phase rather than during peak exercise. In patient 2, the sensor gain was increased after the ET, which resulted in a reduction of symptoms. For patient 3, no adjustments were made, as they remained asymptomatic. In all patients, the HR remained elevated during the initial post-ET period, reflecting a physiological response that is also observed in individuals without pacemaker therapy. Conclusion The TBS used in the screw-fixation LP for rate-responsive pacing, demonstrates an increase in heart rate during exercise testing in all patients. In patients with a delayed peak HR response, optimization was achieved through reprogramming.