Discussion
CVD, SLEEP-DISORDERED BREATHING
To the best of our knowledge, the current study is the first to show that arousal-related transient changes in ventricular repolarization contribute to high repolarization lability reflected by changes in arousal-related QTVi. Irrespective of the cause of sleep arousal, arousal-related QTVi identified a group of older men at higher risk of long-term all-cause and CVD mortality.Studies have shown changes in ventricular repolarization in patients with conditions typically associated with increased arousal burden. For example, patients with sleep-disordered breathing have an increased arousal burden, a prolonged QT interval, and increased QT interval variability,Interestingly, QTVi prior to arousal onset (baseline) was not significantly associated with increased long-term mortality and was comparable between REM and non-REM sleep. The association between arousal-related QTVi and long-term mortality was independent of the baseline QTVi, suggesting the involvement of arousal-related mechanisms. We speculate that arousal-related autonomic and hemodynamic responses may detrimentally affect the heart and transiently expose the individual to increased CV risk during sleep.Frequent arousal results in significant sleep fragmentation and circadian rhythm disturbance. In turn, they contribute to increased CV mortality by various mechanisms involving autonomic nervous system activation, nocturnal BP, and heart rate increases.Several consensusesThe current study had certain limitations. Participants were predominately white men and were predominantly older. Hence our findings cannot be extrapolated to women, other races, or younger individuals. Further studies, including men and women, can help delineate the relationship between cardiac arousal response, sex, and mortality. Our observations are based on a single night. Repeated studies over multiple nights will be required to shed light on day-to-day variations and reproducibility. Also, baseline exposure to various conditions was self-reported rather than systematically ascertained through medical records or direct measurement. We did not consider the possible confounding effects of medications and did not examine the cause of arousal. 