Safety and efficacy of Transcatheter Pacing System demonstrated in initial study


Early performance results of the first-in-human international study of Medtronic’s Micra Transcatheter Pacing System (TPS) have demonstrated the device is safe and effective.

“The miniaturised leadless pacemaker system is a promising new solution that could reduce risks associated with the traditional technology and improve patient satisfaction. Early performance of the first 140 patients provides initial evidence that Micra TPS can safely and effectively be applied,” said lead investigator Philippe Ritter (Hopital Haut-Leveque, Pessac, France) at HRS 2015.

Permanent cardiac pacing is the only effective treatment for symptomatic bradycardia. Complications with conventional transvenous pacing systems are mostly associated with the pacing lead and chest pocket. Micra TPS does not use leads or require a chest pocket. It is implanted from the femoral vein and fixated in the right ventricle and is 93% smaller than conventional pacemakers.

Ritter explained: “It has an accelerometer to drive the rate responsiveness and can communicate with the outside through a conventional programmer. It has a fixation which is quite specific, with flexible retractable nitinol tines. It is MRI compatible and its battery service life is estimated at 10 years.”

The Micra TPS study is a single-arm, multicentre, worldwide trial examining the performance of the self-contained miniaturised leadless pacemaker. Patients were enrolled in the study in 23 centres in Asia-Pacific, Europe and the USA, with 37 physicians implanting the device. This study results served for CE mark approval in April 2015.

The primary safety objective of the study was freedom from major complications related to the device and/or the procedure, measured at six months after implantation, with an assumed performance of greater than 90%. The performance objective was to demonstrate low and stable thresholds at the six-month visit, with an assumed performance of 89% at a threshold less than or equal to 2V, and with an increase of no more than 1.5V relative to implant.

The patient population in the study was mixed, with a wide range of age and weight. The most common primary indications for pacing were a history of permanent or persistent atrial tachyarrhythmia (65%), sinus node dysfunction (16%), and AV block (14%), and 97% of patients had one or more comorbidities.

Ritter presented an initial pre-specified analysis of the study, based on findings from the first 60 patients who passed their three-month follow-up. When the 60th patient passed their three-month follow up, 140 patients had been implanted. There will be two further analyses: a primary objective analysis, gathering 300 patients for six-month follow-up and a long-term performance analysis assembling more than 700 patients over 12 months.

Efficacy was quantified by measuring electrical endurance at implant, pre-discharge, and at one-month and three-month’s follow-up.

All attempts at implanting the device were successful in the 140 patients (100%) measured in the early performance group. One patient died 139 days post-implant, but this was judged to be unrelated to the device and the procedure. No patients were lost to follow-up and there were no discontinued interventions.

There were nine serious adverse events in eight patients, with three different types-dysrhythmias, cardiac complications and groin complications. Two patients required prolonged hospitalisation. Ritter reported: “The serious adverse event rate is 5.7%, which is in line with the 7.3% of serious adverse events, with the same definition for them, at one month in six recent Medtronic trials [of conventional systems].”

And, he reported, there were no unforeseen events, device telemetry issues or dislodgements, and no infections, reoperations or related deaths. These, Ritter pointed out, are “tremendous complications in conventional devices and can lead to re-operations which are dangerous and can be quite life threatening”.

Evaluation of the electrical performance showed an increase in the R-wave sensing amplitude from a mean of 11mV at implant to a mean of 16mV at three-month’s follow-up. The mean value of the pacing capture threshold was consistently below 1V for a pulse duration of 0.24ms nominal value and remained stable over the three months, with impedance close to 700V.

“The 100% implant success is in a very wide range of patients. There have been no procedure-related deaths; the serious adverse event rate with Micra appears to be in line with traditional systems. Electrical performance is excellent and remains stable at three months. Long-term safety and benefit will be further evaluated in the ongoing study.

“If with the very largest population-which is now including 700-plus patients-we found the same, then that will be quite revolutionary. These devices can last for about 10 years as long as conventional devices, but with less volume, which is absolutely fantastic.”

Ritter said now that Micra has been awarded a CE mark it is his preferred device. Although there are no long-term results available yet, he said experience from animal studies gave him confidence in the device.

“In my opinion it will take the place completely of the single-channel devices. This system is not that difficult to implant, it is a simple procedure. [It needs a checklist approach]. But I think surgeons can do that, electrophysiologists can do that, also radiologists could do that.

“This is effective. I am involved in pacing since now 30 years and I never saw such results with conventional leads,” he commented.