Long-term outcomes in leadless Micra transcatheter pacemakers with elevated thresholds at implantation: Results from the Micra Transcatheter Pacing System Global Clinical Trial

BACKGROUND Device repositioning during Micra leadless pacemaker implantation may be required to achieve optimal pacing thresholds. OBJECTIVE The purpose of this study was to describe the natural history of acute elevated Micra vs traditional transvenous lead thresholds. METHODS Micra study VVI patients with threshold data (at 0.24 ms) at implant (n = 711) were compared with Capture study patients with de novo transvenous leads at 0.4 ms (n = 538). In both cohorts, high thresholds were defined as >1.0 V and very high as >1.5 V. Change in pacing threshold (0-6 months) with high (1.0 to <1.5 V) or very high (>1.5 V) thresholds were compared using the Wilcoxon signed-rank test. RESULTS Of the 711 Micra patients, 83 (11.7%) had an implant threshold of >1.0 V at 0.24 ms. Of the 538 Capture patients, 50 (9.3%) had an implant threshold of >1.0 V at 0.40 ms. There were no significant differences in patient characteristics between those with and without an implant threshold of >1.0 V, with the exception of left ventricular ejection fraction in the Capture cohort (high vs low thresholds, 53% vs 58%; P =.011). Patients with an implant threshold of >1.0 V decreased significantly (P <.001) in both cohorts. Micra patients with high and very high thresholds decreased significantly (P <.01) by 1 month, with 87% and 85% having 6-month thresholds lower than the implant value. However, when the capture threshold at implant was >2 V, only 18.2% had a threshold of <1 V at 6 months and 45.5% had a capture threshold of >2 V. CONCLUSIONS Pacing thresholds in most Micra patients with elevated thresholds decrease after implant. Micra device repositioning may not be necessary if the pacing threshold is <2 V. (C) 2017 The Authors. Published by Elsevier Inc. on behalf of Heart Rhythm Society. All rights reserved.