Predictive factors for increase in pacing threshold after transcatheter pacing system implantation owing to micro-dislodgement

Introduction: Achievement of a favorable pacing threshold with a Micra transcatheter pacing system (Micra-TPS) is important for reducing battery depletion; in some cases, the threshold increases shortly after the device is implanted, and a higher pacing threshold may be required. This study aimed to define the causes and predictors of the increase in pacing threshold observed shortly after Micra-TPS implantation. Methods and Results: The study included 64 consecutive patients who underwent Micra-TPS implantation between 2017 and 2020. Patients were divided into two groups depending on their pacing threshold, namely, the increased pacing threshold (IPT) group (threshold increased by ≥0.5 V/0.24 msec within 1 month of implantation) and the stable pacing threshold (SPT) group. Excluding 4 patients we were unable to conduct follow-up on, 9 of the 60 remaining patients (15%) were in the IPT group and 51 (85%) were in the SPT group. The IPT group had significantly lower implant impedance values and higher implant thresholds than the SPT group: 582 ± 59 vs 755 ± 167 Ω (P <0.001) and 1.29 ± 0.87 vs 0.71 ± 0.40 V/0.24 msec (P =0.014), respectively. Implant impedance and threshold may serve as predictors of a threshold increase after implantation (area under the curve: 0.737–0.943 and 0.586–0.926, respectively). Conclusion: An increased pacing threshold was noted shortly after Micra-TPS implantation owing to micro-dislodgement because of insufficient anchoring of the device on the myocardium. Impedance >660 Ω and threshold <1.0 V/0.24 msec may be predictive factors for an increased pacing threshold.