Regulatory Editor

SAN FRANCISCO – Medical science is not yet ready to consign the pacemaker lead to the dustbin of medical history, but an update on a study matching the Nanostim leadless pacemaker by St. Jude Medical with transvenous pacemakers demonstrated that the Nanostim offers the patient some prospect of escaping many of the complications encountered with traditional pacemaker design.

Vivek Reddy of Mount Sinai Hospital in New York presented two-year data for the Leadless II study at the 37th edition of the Heart Rhythm Society's scientific sessions, a study comparing more than 700 Nanostim implants with more than 10,500 transvenous pacemaker (TVP) implants drawn from the Truven Marketscan database of claims data.

Reddy made a point of reminding those in attendance at the May 6 session, "Leadless II was not a randomized study," and he noted that the average ages of the two study groups differed substantially (the TVP population was aged 80 years on average, four years older than the Nanostim group average). However, Reddy highlighted the relevance of the study's inquiry into acute and mid-term complication rates by pointing out that recent data from a Danish registry study confirmed yet again that the rate of complications for TVP units has improved little over the past few years.

The TVP data for Leadless II were drawn from devices implanted between April 2009 and March 2014, and acute complications – defined as those occurring in the first 30 days post-implant – occurred in slightly less than six percent of those on the Nanostim versus nearly 13 percent of the TVP devices. Device dislodgment and pericardial effusion were seen in 1.0 and 1.5 percent in the Nanostim group, respectively, at 30 days, whereas 7.6 percent of the TVP patients experienced adverse events related to their pacemaker leads.

Nearly four percent of the TVP group sustained thoracic trauma, while another two percent experienced an infection. The 24-month rate of complications favored the Nanostim by a large margin (0.6 percent compared to 5.4 percent of the TVP group), although Reddy acknowledged that the TVP data were drawn from patients who, in addition to being older on average, were less healthy than those on the Nanostim, which as yet does not bear an FDA seal of approval.

Still, Reddy said a propensity analysis yielded a similar set of differences in outcomes between the two groups. He observed that extractability of the Nanostim could prove problematic in some instances because "based on the preclinical data, we expect some degree of tissue overgrowth." However, Reddy suggested that a greater volume of experience could improve Nanostim outcomes further. "The Leadless II study was performed by operators who had never performed" implant of the Nanostim, Reddy stated, posing the question of what the comparative numbers would look like if those implanting the TVP units had been similarly inexperienced in that procedure.

When asked whether the data offered any signal in connection with degradation in left ventricular function, Reddy said "we did see that in the Leadless II trial," explaining that four or five patients "subsequently upgraded to dual-chamber pacemakers."

While St. Paul, Minn.-based St. Jude has yet to push the Nanostim past the FDA hurdle and thus is playing catch-up to the Medtronic Micra, the Nanostim is likely to join ranks of the hunted shortly after an FDA approval. Boston Scientific of Marlborough, Mass. is also in pursuit of the leadless pacemaker market with a device the company has dubbed the Empower.

S-ICD registry offers glowing numbers

Lucas Boersma of St. Antonius Ziekenhuis Hospital in Nieuwegein, the Netherlands, presented at HRS on the registry-based Effortless study of the subcutaneous ICD (S-ICD) systems, offering the first glimpse of data from this registry. The analysis of data from more than 980 patients enrolled at 40-plus sites in 10 European nations covered devices that were implanted between August 2009 and December 2014, and Boersma remarked that the underlying registry "provides the largest S-ICD database in the world."

The pre-defined endpoints in this analysis were complications reported at 30 and 360 days along with shock for atrial fibrillation and supraventricular (SV) tachycardia. While follow-up time for each patient reached at least a year, median follow-up time was three years while roughly one in 12 reached 60 months of follow-up. Only 500 of the original patients enrolled were still tracking in the registry at three years.

This was not an elderly population by any means – the median age at enrollment was 48 years – and only 28 percent of the enrollees in the registry were women. Nearly two thirds of the entries in the registry were for primary prevention, and Boersma remarked that the primary endpoints were similar to those used in the FDA pivotal study for the S-ICD, which Boston Scientific, of Marlborough, Mass., acquired in its absorption of Cameron Health in 2012. Approximately three in 10 of the registry patients acquired atrial fibrillation as a consequence of ischemic heart disease, while channelopathy and idiopathic ventricular fibrillation accounted for another 19 percent and six percent, respectively.

Complications arose in 115 patients, most of which were related to device implant, including 24 devices removed for infection. Boersma said there were also several instances in which the generator had shifted. Freedom from complications at 30 days was 96 percent, and nearly that high at 360 days (92 percent). Boersma said, "the most common reason for complications was infection or removal of the device," including 24 device extractions. The rate of inappropriate shock was nearly 12 percent at 3.1 years.

Boersma acknowledged that the rate of follow-up was low given the relatively youthful enrollment, but he remarked, "appropriate therapy was clinically effective in all but one patient." Boersma added, "we cannot be sure about this technology for every patient," but said, "new algorithms will further reduce inappropriate shock."

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