Beat-to-beat cardiac repolarization lability increases during hypoxemia and arousals in obstructive sleep apnea patients

Abstract

Obstructive sleep apnea (OSA) is associated with the progression of cardiovascular diseases, arrhythmias, and sudden cardiac death (SCD). However, the acute impacts of OSA and its consequences on heart function are not yet fully elucidated. We hypothesized that desaturation events acutely destabilize ventricular repolarization, and the presence of accompanying arousals magnifies this destabilization. Ventricular repolarization lability measures, comprising heart rate corrected QT (QTc), short-time-variability of QT (STVQT), and QT variability index (QTVI), were calculated before, during, and after 20,955 desaturations from lead II electrocardiography signals of 492 patients with suspected OSA (52% men). Variations in repolarization parameters were assessed during and after desaturations, both with and without accompanying arousals, and groupwise comparisons were performed based on desaturation duration and depth. Regression analyses were used to investigate the influence of confounding factors, comorbidities, and medications. The standard deviation (SD) of QT, mean QTc, SDQTc, and STVQT increased significantly (P < 0.01), whereas QTVI decreased (P < 0.01) during and after desaturations. The changes in SDQT, mean QTc, SDQTc, and QTVI were significantly amplified (P < 0.01) in the presence of accompanying arousals. Desaturation depth was an independent predictor of increased SDQTc (β = 0.405, P < 0.01), STVQT (β = 0.151, P < 0.01), and QTVI (β = 0.009, P < 0.01) during desaturation. Desaturations cause acute changes in ventricular repolarization, with deeper desaturations and accompanying arousals independently contributing to increased ventricular repolarization lability. This may partially explain the increased risk of arrhythmias and SCD in patients with OSA, especially when the OSA phenotype includes high hypoxic load and fragmented sleep.NEW & NOTEWORTHY Nocturnal desaturations are associated with increased ventricular repolarization lability. Deeper desaturations with accompanying arousals increase the magnitude of alterations, independent of confounding factors, comorbidities, and medications. Changes associated with desaturations can partially explain the increased risk of arrhythmias and sudden cardiac death in patients with OSA, especially in patients with high hypoxic load and fragmented sleep. This highlights the importance of detailed electrocardiogram analytics for patients with OSA.

Keywords: beat-to-beat QT variability; nocturnal desaturation; obstructive sleep apnea; sleep arousal; ventricular repolarization.

Figure 1.

Demonstration of electrocardiogram (ECG) parameters for a desaturation event: detected desaturation event (A); delineated time-matched pre-, within-, and post-desaturation ECG samples (B); calculated RR, QT, and QTc interval time series (C–E, respectively). Desat, desaturation.

Figure 2.

Calculated RR, QT, and QTc interval time series: a shallow desaturation without arousal (A) and a deep desaturation accompanied by an arousal (B). Deep desaturations accompanied by arousals lead to higher decrease in RR intervals and a notable increase in QTc values. Desat, desaturation; QTc, heart rate corrected QT interval.

Figure 3.

The changes in standard deviation of QTc (SDQTc), short-time variability of QT (STVQT), and QT variability index (QTVI) compared with the pre-desaturation measure between desaturations not associated with arousals and desaturations accompanied by arousals in different desaturation depth groups. Statistical tests were performed using Wilcoxon’s signed-rank test. Δ$\text{S}{\text{p}}_{{\text{O}}_2}$, blood oxygen desaturation in percentages; desat, desaturation. *Statistically significant change compared with the pre-desaturation values; +statistically significant change compared with the 3–4.5% group; #statistically significant change compared with all depth groups.

Figure 4.

The changes in the standard deviation of QTc (SDQTc), short-time variability of QT (STVQT), and QT variability index (QTVI) compared with the pre-desaturation measure between desaturations not associated with arousals and desaturations accompanied by arousals in different desaturation duration groups. Statistical tests were performed using Wilcoxon’s signed-rank test. T_des, desaturation duration in seconds; desat, desaturation. *Statistically significant change compared with the pre-desaturation values; +statistically significant change compared with the 10- to 20-s group; #statistically significant change compared with all duration groups.