BACKGROUND: More than half of all sudden cardiac deaths (SCDs) are unwitnessed, but the composition of the unwitnessed SCD population is poorly described.

OBJECTIVE: The purpose of this study was to compare clinical and autopsy characteristics of young unwitnessed SCD subjects, based on the time from last contact to being found dead.

METHODS: All unwitnessed SCD subjects aged 1-35 years in Denmark from 2000-2014 identified through a multisource approach were included. Time from last seen alive to being found dead was dichotomized to <1 hour or 1-24 hours. Clinical characteristics and autopsy results were compared, and predictors of autopsy were assessed by logistic regression.

RESULTS: Of 440 unwitnessed SCD subjects, 366 (83%) had not been seen alive within 1 hour of being found dead. Comorbidities differed between the groups, with more epilepsy (17% vs 5%) and psychiatric diseases (13% vs 7%) in the 24-hour group. Patients in the 24-hour group died more frequently during sleep (64% vs 23%), the autopsy rate was higher (75% vs 61%), and deaths were more often unexplained after autopsy (69% vs 53%). Having been seen within 1 hour of death independently decreased the chance of being autopsied (odds ratio 0.51; 95% confidence interval 0.27-1.00; P = .0497).

CONCLUSION: The majority of unwitnessed SCD subjects had not been seen alive within 1 hour of being found dead. Clinical- and autopsy-related characteristics differed between the 2 groups. Differences were mainly attributable to death-related circumstances and comorbidities. Excluding SCD cases not seen alive within 1 hour of being found dead would severely underestimate the burden of SCD.