This study investigates the day-night pattern of sudden cardiac death in individuals with obstructive sleep apnea (OSA). The researchers reviewed polysomnograms and death certificates of 112 Minnesota residents who died suddenly from cardiac causes between July 1987 and July 2003. They compared the rates of sudden cardiac death from midnight to 6 a.m. among people with OSA and those without, as well as with the general population and expected rates by chance. The results showed that sudden cardiac death from midnight to 6 a.m. was significantly higher in people with OSA (46%) compared to those without OSA (21%), the general population (16%), and expected rates by chance (25%). People with sudden cardiac death from midnight to 6 a.m. had a significantly higher apnea-hypopnea index and a relative risk of 2.57 for sudden cardiac death during this period. The study concludes that individuals with OSA have a peak risk of sudden cardiac death during sleep, which contrasts with the nadir risk observed in the general population during the same period. The severity of OSA correlated directly with the risk of nocturnal sudden cardiac death, suggesting that severe OSA may be associated with a higher risk of sudden cardiac death.This study investigates the day-night pattern of sudden cardiac death in individuals with obstructive sleep apnea (OSA). The researchers reviewed polysomnograms and death certificates of 112 Minnesota residents who died suddenly from cardiac causes between July 1987 and July 2003. They compared the rates of sudden cardiac death from midnight to 6 a.m. among people with OSA and those without, as well as with the general population and expected rates by chance. The results showed that sudden cardiac death from midnight to 6 a.m. was significantly higher in people with OSA (46%) compared to those without OSA (21%), the general population (16%), and expected rates by chance (25%). People with sudden cardiac death from midnight to 6 a.m. had a significantly higher apnea-hypopnea index and a relative risk of 2.57 for sudden cardiac death during this period. The study concludes that individuals with OSA have a peak risk of sudden cardiac death during sleep, which contrasts with the nadir risk observed in the general population during the same period. The severity of OSA correlated directly with the risk of nocturnal sudden cardiac death, suggesting that severe OSA may be associated with a higher risk of sudden cardiac death.