Association between computed tomography-verified pacing location of Micra™ leadless pacemakers and characteristics of paced electrocardiograms in bradycardia patients

Introduction: The leadless pacemakers are implanted routinely under fluoroscopic image, yet the pacing sites and corresponding paced electrocardiography (ECG) remain unclear. This study was to determine the computed tomography (CT)-verified location of the leadless Micra™ pacemakers (Micra™) and ECG characteristics. Methods: : 20 consecutive patients who met the pacemaker indications for bradycardia and underwent fluoroscopy assisted Micra TM implantation were enrolled. All subjects underwent a postoperative CT scan to determine the precise location of the Micra TM pacing tip. Paced 12-lead ECG characteristics were analysed and correlated with the Micra TM tip location. Results: : In the nine partitions of fluoroscopic RAO images, 14 (70%) of 20 patients had the Micra TM tip in zone 5, 5 (25%) in zone 6 and 1 in zone 2. Reconstructed CT 3-D cardiac images found Micra TM tips mostly clustered near the anterior insertion between the RV septum and free wall with 12 cases at the insertion-septal side and 8 at the free-wall side. ECG morphological analysis found that the peak deviation index in ECG lead V1 was 0.402±0.061 for Micra TM tips at the insertion-septal side and 0.542±0.053 in the free-wall side (P <0.001 between two sides) and paced clumsy R wave was often observed for tips at the free-wall side though there was no difference in QRS duration between two sides. Conclusion: . In routine Micra TM implantation, the pacing sites were often located in the anterior insertion region, either at the insertion-septal or free-wall side. The ventricular activation propagation likely depended on the pacing sites.