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

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.

This study aimed to characterize associations among habitual sleep duration, QTVI, and all-cause mortality.

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.

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).

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.