Unconfirmed media reports say Nancy Guthrie's pacemaker stopped syncing with her Apple devices. Here's what that means.

Nancy Guthrie’s 2 a.m. pacemaker spike on the day she vanished could mean that the elderly woman was involved in a heart rate-surging struggle with her possible captors, a lead cardiologist speculated Thursday.

One part of the investigation into the disappearance of “Today” show host Savannah Guthrie’s mother focuses on the missing woman’s implanted medical device.

Authorities are investigating the disappearance of Nancy Guthrie, 84, who was last seen at her Arizona home on Sat. Jan. 31

Nancy Guthrie’s pacemaker reportedly stopped syncing with her Apple devices predawn Sunday morning – as the Arizona sheriff leading the missing person case called a surprise press conference for late Tuesday morning.

A law enforcement source told Fox News Digital that the 84-year-old's pacemaker last synced with her Apple devices around 2 a.m. on Sunday.

A man who had a pacemaker fitted when he was just nine years old has gone on to complete two marathons. Kieran Cooper, of Blackpool, Lancashire, was born with a heart condition and was never allowed to play sports as a child. He said he found this incredibly difficult but "thankfully there is a different mindset nowadays".