Sleep-Disordered Breathing Destabilizes Ventricular Repolarization

BACKGROUND: Sleep-disordered breathing (SDB) is associated with an increased risk of cardiac arrhythmias, sudden cardiac death, and all-cause mortality. This study investigates the mechanisms underlying this association by examining the effects of prevalent and incident SDB and intermittent hypoxia on ventricular repolarization lability. METHODS: Electrocardiographic recordings from three cohorts were used for this study: (1) a cross-sectional sample of 61 participants with severe SDB and a matched group without SDB; (2) a longitudinal sample of 26 participants without SDB at baseline who developed SDB after a 5 year follow-up, and a matched group without SDB; and (3) a cohort of 19 healthy adults exposed to intermittent hypoxia or ambient air. Mean heart rate, heart rate variability (SDNN), and QT variability index (QTVI), a measure of ventricular repolarization lability, were calculated from one-lead ECG recordings. RESULTS: In the cross-sectional sample, participants with severe SDB had larger QTVI (P = 0.027), heart rate (P = 0.028), SDNN (P = 0.018), and hypoxemia burden as assessed by the total sleep time with oxygen saturation less than 90% (TST90; P < 0.001) than those without SDB. TST90, but not the frequency of arousals, was an independent predictor of QTVI (P = 0.017). Both heart rate and QTVI were predictive of all-cause mortality. In the longitudinal sample with incident SDB, QTVI increased from -1.23 {+/-} 0.15 to 0.86 {plus minus} 0.14 (P = 0.017) over the 5-year follow-up period. Finally, in the cohort of healthy adults, 4 hours of exposure to intermittent hypoxia increased heart rate (P = 0.001) and QTVI (P = 0.016). CONCLUSIONS: Prevalent and incident SDB are associated with increased ventricular repolarization instability which predisposes to ventricular arrhythmias and sudden cardiac death. Intermittent hypoxemia can destabilize ventricular repolarization and is a likely mediator of increased mortality in SDB.