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

ABSTRACT: Background Short and long sleep durations have been linked to 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 To characterize associations between habitual sleep duration, QTVI, and all-cause mortality. Methods Data from 1,123 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 hours/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 assessed the QTVI-mortality association and included a sleep duration-by-QTVI interaction term. Results Both short (≤5 hours) and long (≥9 hours) sleep were associated with higher QTVI compared with 8 hours after adjustment for demographic and clinical covariates (ΔQTVI=0.18, 95% 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 (HR=2.14, 95% CI 1.45–3.17). The QTVI–mortality association varied by sleep duration (p=0.04 for interaction), with the strongest effect in those reporting ≤5 hours of sleep (HR=3.12, 95% CI 1.85–5.26). Conclusions In adults without sleep-disordered breathing, short and long habitual sleep were associated with increased ventricular repolarization lability. Elevated QTVI independently predicted all-cause mortality, particularly in short sleepers, suggesting that sleep duration may influence electrophysiologic vulnerability and arrhythmic risk.