Abstract 12920: Beat-to-Beat QT Interval Variability While Awake, but Not During Sleep, is Associated With All-Cause Mortality
Introduction: Electrocardiographic markers of autonomic tone, in particular heart rate variability (HRV) and QT-interval variability index (QTVI), have previously been shown to correlate with adverse outcomes. How these metrics perform during wake compared with sleep, when sympathetic tone is lower, is unclear. We assessed the hypothesis that lower HRV and elevated QTVI during wakefulness, but not sleep, would correlate with mortality.
Methods: We performed a nested case-control analysis within the Sleep Heart Health Study, a prospective study of 6441 subjects who underwent polysomnography, with collection of sleep and ECG data. Cases died of any cause during 8 years of follow-up, and controls were matched for age, gender, race, smoking status, body-mass index, baseline cardiovascular disease, and respiratory-disturbance index. ECGs were analyzed in 5-minute epochs using a previously validated semi-automated method of R-wave detection, with QT-interval matching to a user-defined template. Differences between groups were assessed using a paired t-test.
Results: A total of 215 case-control pairs were identified. Overnight (wake and sleep), mean heart rate was slightly higher in cases than in controls (67.1 ± 9.6 vs 65.3 ± 8.5 bpm, p = 0.03), but no significant differences were found in measures of HRV (SDNN, RMSSD, or pNN50) or QT variability (QTVI or coherence). During awake periods, cases had higher QTVI (-0.98 ± 0.46 vs -1.11 ± 0.39, p=0.04), and lower coherence (0.31 ± 0.10 vs 0.34 ± 0.11, p=0.008) compared to controls, while HRV measures remained similar. In contrast, during sleep, no significant differences were noted in these measures.
Conclusion: During periods of wake, but not sleep, increased lability in ventricular repolarization (as measured by high QTVI and low coherence) is associated with all-cause mortality. These data suggest that QT variability during periods of greater sympathetic stimulation may be more predictive of outcomes such as mortality.
- © 2011 by American Heart Association, Inc.