Early Performance of a Miniaturized Leadless Cardiac Pacemaker

The Micra Transcatheter Pacing Study

Philippe Ritter; Gabor Z. Duray; Clemens Steinwender; Kyoko Soejima; Razali Omar; Lluís Mont; Lucas VA Boersma; Reinoud E. Knops; Larry Chinitz; Shu Zhang; Calambur Narasimhan; John Hummel; Michael Lloyd; Timothy Alexander Simmers; Andrew Voigt; Verla Laager; Kurt Stromberg; Matthew D. Bonner; Todd J. Sheldon; Dwight Reynolds


Eur Heart J. 2015;36(37):2510-2519. 

In This Article

Abstract and Introduction


Aims Permanent cardiac pacing is the only effective treatment for symptomatic bradycardia, but complications associated with conventional transvenous pacing systems are commonly related to the pacing lead and pocket. We describe the early performance of a novel self-contained miniaturized pacemaker.

Methods and results Patients having Class I or II indication for VVI pacing underwent implantation of a Micra transcatheter pacing system, from the femoral vein and fixated in the right ventricle using four protractible nitinol tines. Prespecified objectives were >85% freedom from unanticipated serious adverse device events (safety) and <2 V 3-month mean pacing capture threshold at 0.24 ms pulse width (efficacy). Patients were implanted (n = 140) from 23 centres in 11 countries (61% male, age 77.0 ± 10.2 years) for atrioventricular block (66%) or sinus node dysfunction (29%) indications. During mean follow-up of 1.9 ± 1.8 months, the safety endpoint was met with no unanticipated serious adverse device events. Thirty adverse events related to the system or procedure occurred, mostly due to transient dysrhythmias or femoral access complications. One pericardial effusion without tamponade occurred after 18 device deployments. In 60 patients followed to 3 months, mean pacing threshold was 0.51 ± 0.22 V, and no threshold was ≥2 V, meeting the efficacy endpoint (P < 0.001). Average R-wave was 16.1 ± 5.2 mV and impedance was 650.7 ± 130 ohms.

Conclusion Early assessment shows the transcatheter pacemaker can safely and effectively be applied. Long-term safety and benefit of the pacemaker will further be evaluated in the trial.


Permanent cardiac pacing, the only effective treatment for symptomatic bradycardia, reduces symptoms and recurrence of syncope, and improves survival in high-risk populations.[1–3] Since their introduction in the 1960s, pacemakers have shrunk in size and grown in sophistication, yet their basic function remains to be sustaining a normal heart rate. Conventional pacing systems consist of a pacemaker containing the electronics and battery typically implanted in a subcutaneous pocket in the chest. One or more leads threaded from the device pocket through veins into the heart conduct the pacing therapy to the desired pacing site. When veins cannot be used, a surgical procedure includes implanting epicardial leads that link the heart to the device. Despite the reduction in complications due to technological advances, serious adverse events can still be encountered. These are reported to be 20% at 5 years, with highest contributions related to the pacing lead (~11%) and pocket (~ 8%),[4] including pneumo/haemothorax after subclavian vein puncture, pocket haematoma, erosion or infection, vein stenosis or occlusion, endocarditis, tricuspid valve trauma, connection troubles, lead fractures, and other malfunctions.[5–8] Micra™ transcatheter pacing system (TPS, Model MC1VR01, Medtronic plc, Mounds View, MN, USA) is a miniaturized single-chamber pacemaker system that is delivered via catheter through the femoral vein and implanted directly inside the right ventricle (RV) of the heart. This new technology is feasible due to advances in miniaturization (high-density battery), low-power electronics, catheter delivery systems, novel materials (nitinol), and electrodes being directly placed on the pacemaker capsule. This eliminates the need for a device pocket and insertion of a pacing lead, thereby eliminating an important source of complications associated with traditional pacing systems while providing similar benefits.

The purpose of this report is to summarize the early performance of the TPS using pre-specified safety and efficacy objectives from the Micra Transcatheter Pacing System Study. These data are being used to support European regulatory submission.