The Micra Transcatheter Pacing System (TPS)—which is about 10-fold smaller than the conventional pacemaker and is implanted from the femoral vein and fixed in the right ventricle—was safe and effective in a range of patients who required ventricular pacing. Philippe Ritter, MD, Hospital Haut-Lévèque, Pessac, France, presented data from the Micra Transcatheter Pacing Study [Ritter P et al. Eur Heart J. 2015].

Currently, the only treatment for symptomatic bradycardia is permanent cardiac pacing. However, transvenous pacing systems may result in serious adverse events (AEs) in up to 12.4% of patients [Udo EO et al. Heart Rhythm. 2012]. The purpose of this study was to determine if the Micra TPS was effective and resulted in fewer serious AEs.

In this international phase 3 trial, patients with a class I or II indication for ventricular pacing [Epstein AE et al. Heart Rhythm. 2008] received the Micra TPS system. The Micra TPS system is about 10 times smaller than the conventional pacemaker and consists of an intracardiac accelerometer with flexible tines. At baseline, the median age was 78 years; 61% were men; and the median body mass index was 26 kg/m². In addition, 65% were diagnosed with bradycardia with permanent or persistent atrial tachyarrhythmia or atrial fibrillation; 16% had sinus node dysfunction; 14% had atrioventricular block; and 6% had another indication.

The primary safety end point was freedom from major Micra TPS–associated complications or procedures in the 6 months following implantation. The primary efficacy end point was a low and stable pacemaker threshold at 6 months. This analysis of 6-month outcomes included data from 140 patients, and analyses using longer term outcomes are planned.

The mean implantation time was 37 minutes, and the success rate was 100%. The Micra TPS implant was placed within the apex in 77% of patients, in the septum in 16%, in the midseptum in 6%, and in the right ventricular outflow tract in 1%. The median deployment per patient was 1, with successful first deployment in 59%, success achieved within 2 deployments in 81%, and success achieved within 4 deployments in 96%.

The serious AE rate was 5.7%, and 1.4% of patients required prolonged hospitalization; however, there were no device telemetry issues, dislodgements, infections, reoperations, or device-related deaths. Serious AEs included transient atrioventricular block, right bundle branch block, ventricular tachycardia, and ventricular fibrillation (Table 1).

The R-wave sensing amplitude was a mean of 11 mV at time of implant and 16 mV at 3 months. The pacing capture threshold remained steady—0.64 V at the time of implant and 0.51 V at 3 months. Pacing impedance was 731 Ω at the time of implant and 651 Ω at 3 months.

In conclusion, Prof Ritter stated that according to the early performance measurements, the Micra TPS system was safe and effective in a large range of patients. However, long-term safety and efficacy will be studied in an ongoing trial.