The Micra leadless pacemaker made by Medtronic (NYSE:MDT) passed its initial safety and efficacy endpoints in a global clinical trial, researchers said today at the annual Heart Rhythm Society meeting in Boston.

Initial data from the single-arm Micra TPS trial from 96 patients at the 1-month mark showed a 100% successful implantation rate for the Micra device, Dr. Philippe Ritter of the University Hospital of Bordeaux said today. The Micra device is implanted inside the heart via catheter.

"I’ve been involved in pacing for 30 years and I’ve never seen such results," Ritter said.

There were 8 serious adverse events in 7 patients in the trial, some likely due to mechanical stimulation by the catheter, but all were easily managed and resolved, Ritter said. One patient, in whom physicians tried to reposition the device multiple times, suffered pericardial effusion without tamponade and had a myocardial infarction 3 days later. Ritter said that patient is still alive.

The Micra device is shorter and wider than the rival Nanostim leadless pacer St. Jude Medical (NYSE:STJ) acquired in 2013, Ritter said, but the major difference lies in how the device is attached to the myocardium.

"The Nanostim has a very big screw and you have to be careful not to overturn the screw," Ritter explained. "But whichever system you use, you have to be well trained, because this is a new technique."

Nanostim won CE Mark approval in the European Union in January 2014. Medtronic’s Micra won a CE Mark just last month.