Sleep-Disordered Breathing Destabilizes Ventricular Repolarization

Abstract

Rationale: Sleep-disordered breathing (SDB) increases the risk of cardiac arrhythmias and sudden cardiac death.

Objectives: 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 a higher risk for cardiac arrhythmias, sudden cardiac death, and mortality.

Methods: Three distinct cohorts were used for the current study. The first cohort, used for cross-sectional analysis, was a matched sample of 122 participants with and without severe SDB. The second cohort, used for longitudinal analysis, consisted of a matched sample of 52 participants with and without incident SDB. The cross-sectional and longitudinal cohorts were selected from the Sleep Heart Health Study participants. The third cohort comprised 19 healthy adults exposed to acute intermittent hypoxia and ambient air on two separate days. Electrocardiographic measures were calculated from one-lead electrocardiograms.

Results: Compared to those without SDB, participants with severe SDB had greater QTVI (-1.19 in participants with severe SDB vs. -1.43 in participants without SDB, P = 0.027), heart rate (68.34 vs. 64.92 beats/minute; P = 0.028), and hypoxemia burden during sleep as assessed by the total sleep time with oxygen saturation less than 90% (TST₉₀; 11.39% vs. 1.32%, P < 0.001). TST₉₀, but not the frequency of arousals, 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, exposing healthy adults to acute intermittent hypoxia for four hours progressively increased QTVI (from -1.85 at baseline to -1.64 after four hours of intermittent hypoxia; P = 0.016).

Conclusions: Prevalent and incident SDB are associated with ventricular repolarization instability, which predisposes to ventricular arrhythmias and sudden cardiac death. Intermittent hypoxemia destabilizes ventricular repolarization and may contribute to increased mortality in SDB.

Keywords: Beat-to-beat QT variability index; QTVI; Sleep Heart Health Study; Sleep apnea; intermittent hypoxemia; intermittent hypoxia.

Figure 1.. QTVI was higher in participants with severe SDB.

The diagram shows the mean QTVI measurements for participants without SDB (N = 61, red) and with severe SDB (N = 61, blue).

Figure 2.. Incident SDB destabilized ventricular repolarization.

The diagram shows QTVI for participants with and without incident SDB. QTVI significantly increased in participants who developed SDB. N = 26 in each group. P values are for the paired samples t test between baseline and follow-up measurements for each group.

Figure 3.. Temporal effects of intermittent hypoxia on electrocardiographic measures.

The left panel shows data on one subject during ~ 20 minutes of exposure to intermittent hypoxia. Cyclical changes were noted in the heart rate and QT interval with intermittent hypoxia. The right panel shows the NN interval, SDNN, LF/(HF+LF) ratio, and QTVI of the 19 subjects for each hour of the four hours of exposure to intermittent hypoxia and normoxia. * indicates P < 0.05 for comparing the two conditions during the corresponding hour.