59-05: Accelerometer based Rate Adaptive Pacing in Micra™ Transcatheter Pacemaker Free

Introduction: The Micra transcatheter pacemaker has similar functionality to conventional transvenous VVIR pacing systems despite its small size (0.8 cc) and intracardiac location. It provides rate responsive (RR) pacing using a programmable 3-axis accelerometer designed to detect patient activity in the presence of cardiac motion. We evaluated the RR performance during treadmill tests to maximum exertion.

Methods: Patients underwent treadmill testing at 3 or 6-months post-implant with RR programming at physician discretion. Normalized sensor indicated rate (SIR) relative to the programmed upper sensor rate was modeled as a function of normalized workload in metabolic equivalents (METS) relative to maximum METS achieved during the test. A normalized MET and SIR was determined at the end of each 1 minute treadmill stage. The proportionality of SIR to workload was evaluated by comparing the slope from this relationship to the prospectively defined tolerance margin of 0.65 to 1.35. A slope of 1.0 would indicate linear RR throughout the workload range.

Results: A total of 69 treadmill tests were attempted by 44 patients at 3 and 6-months post-implant. 30 tests from 20 patients that completed ≥4 stages with a slope of 0.86 (95% CI = 0.75-0.98) confirming proportionality to workload. In over/under responsive patients, further adjustment of the RR parameters may have improved response. Activity counts and SIR are shown for an example test in the left Figure. The cumulative normalized slope result for all patients is shown in right Figure.

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Conclusion: Accelerometer based rate response was linear to workload confirming appropriate RR is achievable with an entirely intracardiac pacing system.