It's hard for autopsies to find evidence of a seizure so using video from home monitors to reevaluate deaths "is actually very clever," said Dr. Marco Hefti, a neuropathologist at the University of Iowa who wasn't involved with the study but has also investigated SUDC.
"It's not that parents need to be stressing out, panicking about every febrile seizure," he cautioned. But Hefti said it's time for additional research, including animal studies and possibly sleep studies in children, to better understand what's going on.
SUDC is estimated to claim over 400 lives a year in the U.S. Most occur during sleep. And just over half, about 250 deaths a year, are in 1- to 4-year-olds.
Sudden death in babies occurs more often and gets more public attention - along with more research funding that in turn has uncovered risk factors and prevention advice such as putting infants to sleep on their backs. But SUDC happens to youngsters long past the age of SIDS. The Fells had never even heard of it until Hayden died.
Hayden experienced his first seizure shortly before his first birthday when a cold-like virus sparked a fever. Additional mild bugs triggered several more but Hayden always rapidly bounced back - until the night in November 2022 when he died.
Other recent studies, at NYU and by a team at Boston Children's Hospital, have hunted genetic links to SUDC - finding that some children harbored mutations in genes associated with heart or brain disorders, including irregular heartbeats and epilepsy.
Heart problems, including those mutations, couldn't explain the deaths of the toddlers in the video study, Devinsky said. He cautioned that far more research is needed but said epilepsy patients sometimes experience difficulty breathing after a seizure that can lead to death - and raised the prospect that maybe some SIDS deaths could have seizure links, too.
Hayden's mom, Katie Czajkowski-Fell, hopes the video evidence helps finally lead to answers.
"His life, it was too precious and too important for us to not try and do something with this tragedy."