Abstract
Sleep-disordered breathing (SDB) increases the risk of cardiac arrhythmias and sudden cardiac death.
To characterize the associations between SDB, intermittent hypoxemia, and the beat-to-beat QT variability index (QTVI), a measure of ventricular repolarization lability associated with cardiac arrhythmias and sudden cardiac death.
Three distinct cohorts were used: (1) a matched sample of 122 participants with and without severe SDB for cross-sectional analysis, (2) a matched sample of 52 participants with and without incident SDB for longitudinal analysis, and (3) a sample of 19 healthy adults exposed to acute intermittent hypoxia and ambient air on two separate days. The cross-sectional and longitudinal cohorts were the Sleep Heart Health Study participants with no known comorbidities who were not on any drugs known to affect cardiac repolarization and satisfied the inclusion criteria. Electrocardiographic measures were calculated from one-lead electrocardiograms.
Participants with severe SDB had greater QTVI than those without SDB (P = 0.027). Total sleep time with less than 90% oxygen saturation, but not the arousal frequency, was a predictor of QTVI. QTVI during sleep was predictive of all-cause mortality. With incident SDB, mean QTVI increased from -1.23 to -0.86 over 5 years (P = 0.017). Finally, experimental exposure of healthy adults to acute intermittent hypoxia for four hours progressively increased QTVI (P = 0.016).
The results show that both prevalent and incident SDB are associated with ventricular repolarization instability and suggest intermittent hypoxemia as the underlying mechanism that may contribute to increased mortality in SDB.