After six months of nonsurgical implantation with an active-fixation leadless cardiac pacemaker, 90 percent of patients had an acceptable pacing threshold and sensing amplitude, according to a prespecified analysis of an ongoing study.

In addition, 6.7 percent of patients had device-related serious adverse events, including 1.7 percent with device dislodgement with percutaneous retrieval, 1.3 percent with cardiac perforation and 1.3 percent with pacing-threshold elevation requiring percutaneous retrieval and device replacement.

Lead researcher Vivek Y. Reddy, MD, of the Icahn School of Medicine at Mount Sinai in New York City, and colleagues published their results online in the New England Journal of Medicine on Aug. 30. The findings were also presented at the European Society of Cardiology Congress in London.

Reddy and his colleagues mentioned that the mean pacing threshold and sensing values at six months were similar to those observed with conventional transvenous leads.

They added that a previous study found 3.2 percent of patients implanted with conventional ventricular pacemakers had complications, while the rate of cardiac perforation was similar in the LEADLESS II study and previous studies that examined transvenous leads.

“Leadless cardiac pacemakers have the potential to overcome many of the complications of conventional transvenous pacemakers,” Reddy said in a news release. “Transvenous leads are considered the Achilles’ heel of conventional pacemakers because they are particularly susceptible to complications.”

In the LEADLESS II study, the researchers assessed the clinical safety and efficacy of the Nanostim leadless cardiac pacemaker in patients who required permanent ventricular pacing. The Nanostim device is not FDA-approved, although it is approved in Europe.

St. Jude Medical, the manufacturer of the pacemaker, funded the trial. The FDA and the institutional review board at each participating center approved the premarket study.

Between February 2014 and June 2015, the researchers enrolled 526 patients at 56 sites in three countries. The mean age was 75.8, and 61.8 percent of patients were males.

Of the patients, 55.9 percent had atrial fibrillation with atrioventricular block, 8.7 percent had sinus rhythm with high-grade atrioventricular block and 35.4 percent had sinus bradycardia with infrequent pauses or syncope.

The researchers noted that 95.8 percent of patients had their pacemakers successfully implanted, while 70.2 percent did not require device repositioning after initial deployment. The mean duration of hospital stay from implantation to discharge was 1.1 days.

This analysis included 300 patients who completed the 6-month follow-up as of June 2015. The device was successfully implanted in 289 patients.

Of the 289 patients, 270 met the primary efficacy end point of an acceptable pacing threshold and an acceptable sensing amplitude through six months. Of the remaining 19 patients, 16 had inadequate sensed R-wave amplitudes, four had inadequate pacing capture threshold and one had both inadequate pacing and inadequate sensing.

In the total cohort, 28 patients died during the follow-up period, but none of the deaths were considered to be device-related. However, the clinical events committee classified two deaths as procedure-related.