Habitual sleep duration and QT variability index: Correlates of ventricular repolarization lability and all-cause mortality

Background Habitually short and long sleep duration have been associated with adverse cardiovascular outcomes, but their potential effects on ventricular repolarization lability are unknown. The QT variability index (QTVI) is a validated electrocardiographic measure of ventricular repolarization lability that predicts sudden cardiac death and all-cause mortality. Objective This study aimed to characterize associations among habitual sleep duration, QTVI, and all-cause mortality. Methods Data from 1123 adults in the Sleep Heart Health Study without sleep-disordered breathing were analyzed. Self-reported habitual sleep duration was categorized as ≤5, 6, 7, 8 (reference), or ≥9 h/night. QTVI was derived from a single-lead electrocardiogram during in-home polysomnography. Associations between sleep duration and QTVI were examined using robust linear regression. Proportional hazards regression was used to assess the association between QTVI and all-cause mortality. Results Both short (≤5 hours) and long sleep duration (≥9 hours) were associated with higher QTVI than 8 hours of habitual sleep after adjustment for demographic and clinical covariates (ΔQTVI = 0.18; 95% confidence interval [CI] 0.05-0.31; ΔQTVI = 0.15; 95% CI 0.02-0.28, respectively). Higher QTVI predicted greater mortality risk, with the highest quartile associated with more than double the risk (hazard ratio 2.14; 95% CI 1.45-3.17). The QTVI-mortality association varied by sleep duration (P =.04 for interaction), with the strongest effect in those reporting ≤5 hours of sleep (hazard ratio 3.12; 95% CI 1.85-5.26). Conclusion In adults without sleep-disordered breathing, short and long habitual sleep duration were associated with increased ventricular repolarization lability. Elevated QTVI independently predicted all-cause mortality, particularly in short sleepers, suggesting that sleep duration may influence electrophysiological vulnerability and arrhythmic risk.