LONDON – A wireless pacemaker that is secured within the right ventricle of the heart proved both effective and safe in a prospective, nonrandomized, multicenter study.
Interim results obtained for 300 patients at 6 months’ follow-up in the LEADLESS II study showed that the primary efficacy endpoint of both an acceptable pacing threshold and an acceptable sensing amplitude was achieved in 90% of patients, and the primary safety endpoint of freedom from device-related serious adverse events was achieved in 93.3%.
Dr. Vivek Reddy
Both of these findings exceeded the performance goal of 85% set in the study, said principal study investigator Dr. Vivek Reddy at the annual congress of the European Society of Cardiology.
“Regular pacemakers are very reliable devices; they’ve been around for half a century,” said Dr. Reddy, who is professor of medicine at Mount Sinai Hospital in New York. “Having said that, they are not perfect,” he observed.
Conventional pacemakers require surgical implantation in the chest, and the wires or leads that go from the device need to be embedded in the vasculature of the heart itself. While the risk of complications is low (around 4% of all implanted devices), when they do happen they usually occur around the site where the pacemaker is implanted or involve placement of the leads in veins.
In contrast, the small cylindrical Nanostim device used in the study is a fully self-contained leadless pacemaker that can be nonsurgically implanted and removed via a catheter threaded through the femoral vein and into the patient’s right ventricle. It is about the size of an AAA battery and, based on the study’s findings, has a potential battery life of 15 years. This is comparable to similar standard single-chamber ventricular pacemakers, according to the manufacturer, St. Jude Medical.
The feasibility of using the device was first shown in the LEADLESS study (Circulation 2014;129:1466-71) and are now confirmed in the LEADLESS II study, which has enrolled 526 patients to date, with successful implantation of the device in 504 patients.
The mean age of the mostly male (61.8%) study cohort was 76 years, with the primary indication for pacemaker placement being atrial fibrillation with atrioventricular block in 55.9%.
The study was performed in 56 centers in the United States, Canada, and Australia and involved 100 operators, only one of whom had prior experience with leadless pacing, Dr. Reddy observed. On average the leadless device was placed within a half hour, and the majority (70.2%) did not require repositioning of the device during the original procedure.
The rate of serious device-related adverse events, such as dislodgement warranting percutaneous retrieval or cardiac perforation, was low, at a rate of 6.7% overall and 1.7% and 1.3%, respectively, with just 1.3% of patients needing to have the device removed because of an increased pacing threshold. There were no device-related deaths, but two deaths occurred that were thought to be procedure related. This is comparable to traditional pacemakers, Dr. Reddy said, although he noted that he was referring to historical controls as this was not a randomized trial.
“The device was shown to be retrievable in a subgroup of seven patients who needed a replacement at a mean of 160 days after implantation,” he noted. Due to the relatively short duration of follow-up, however, “we really can’t talk about what happens with extended follow-up and what happens 5, 10, or 15 years down the line whether we retrieve the devices or simply abandon them and put in a second device.”
The study included patients who had an indication for a single-chamber pacemaker only. Dr. Reddy noted that one of the study limitations is that the device is not suitable for patients needing dual-chamber pacing. The observational nature of the trial also limits the conclusions that can be drawn, and the device does not provide electrocardiogram data.
The Nanostim device is one of two self-contained, miniature wireless pacemakers given marketing authorization in Europe, but both have yet to be approved by the Food and Drug Administration. The other device, Medtronic’s Micra Transcatheter Pacing System, is also placed in the right ventricle and is being studied in the Micra Transcatheter Pacing Study, with promising first-in-human results presented recently at Heart Rhythm 2015.
St. Jude Medical funded the study. Dr. Reddy has received grant support, acted as a consultant to, and received stock options in Nanostim from the company.