A study of the Nanostim leadless pacemaker made by Abbott’s St. Jude Medical subsidiary pinpoints the cause of a battery depletion issue
A study of the Nanostim leadless pacemaker Abbott acquired this year when it bought St. Jude Medical, presented last week at the annual Heart Rhythm Society conference, found that a battery depletion problem was due to the lithium ion cells being too dry.
St. Jude put a hold on Nanostim implantations last October, after receiving 7 reports of lost telemetry and pacing output. There were no reports of patient injuries associated with the malfunctions. Barclays analysts said at the time that St. Jude was pursuing a software fix to detect any increase in the rate of battery problems, and may be in talks with a battery manufacturer to develop a different battery for Nanostim.
According to the study presented at HRS 2017, “The Nanostim Leadless Pacemaker: Battery Failures and Worldwide Chronic Device Retrieval,” there were 1,423 Nanostim implants worldwide as of March 2017. Of those, there were 28 failures of the device’s lithium carbon monofluoride (lithium CFx) batteries, for a failure rate of 1.97%.
“Analysis revealed not a malfunction of voltage depletion of Lithium or CFx, but rather increased impedance from insufficient electrolyte availability (ie, cell dryness),” the researchers wrote after the explanted Nanostim units were put through a destructive testing regimen.
The success rate for retrieving the devices was 90.4% (47 of 52) at a mean of 1 year after St. Jude’s warning last fall, according to the study. The pacer’s proximal hub was inaccessible in 4 patients and a detached docking button during the 5th unsuccessful retrieval try. Of the 20 pre-warning attempts, 95% were successful, for an overall retrieval success rate of 91.7% and 1 case of arteriovenous fistula.
Eighty-five patients received an additional pacemaker without having their Nanostim retrieved, with no adverse device-to-device interactions, according to the study.
“As with standard pacers, LPs are subject to critical battery failures. Chronic retrievability looks promising with >90% of LPs successfully retrieved percutaneously,” the researchers wrote.