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A leadless pacemaker shown to be safe during a patient's life just might explode upon the user's cremation, two clinicians warned.

The Nanostim pacemaker's small size -- small enough to be delivered transfemorally and implanted in the right ventricle without leads -- was described as "paradigm changing" when the LEADLESS II study safety and efficacy results were reported in the New England Journal of Medicine last year.

However, those same advantages later on, Madhav Bhargava, MB, of Safdarjung Hospital in India, and Raghav Bhargava, MB, of Royal Shrewsbury Hospital in the U.K., wrote in a letter to the NEJM editors.

Because the Nanostim's battery is a lithium carbon monofluoride-polycarbon fluoride device, it has a "high density of energy," the pair wrote, and "it is hypothesized that the greater the energy density of a battery, the greater the risk of explosion."

They argued that, unlike traditional pacemakers, leadless models are hard to remove and may not be detected with handheld metal detectors. Explantation likely requires "a complete autopsy," which may be "socially unacceptable."

"The explantation of these devices for the purpose of cremation has social, cultural, and legal implications that must be considered until it is proved that they can safely withstand the process of cremation," they concluded.

However, LEADLESS II investigator , of the Mount Sinai Hospital in New York, wasn't so concerned.

"The volume of the lithium carbon monofluoride battery that powers the leadless cardiac pacemaker is quite small" -- measuring approximately 1 cm³ -- therefore "rupture of the device during cremation does not present a substantial risk to surrounding life or property," Reddy argued in a response printed alongside the letter.

To date, "the cremation of deceased patients with implanted leadless pacemakers has been performed worldwide without any adverse consequences," he noted.

The Nanostim's battery is expected to last an average of 15 years.

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