Effect of continuous positive airway pressure therapy on circadian patterns of cardiac repolarization in patients with obstructive sleep apnoea: data from a randomized trial.

ABSTRACT

BACKGROUND: Obstructive sleep apnoea (OSA) has been proposed as an independent risk factor for sudden cardiac death (SCD). This study takes advantage of a previous randomized trial and seeks to evaluate circadian patterns of the QTc-interval, a marker of cardiac repolarization and biomarker for SCD, in patients with OSA. We hypothesized that patients with OSA would exhibit longest QTc during the night-time and that continuous positive airway pressure (CPAP) therapy would reverse this. METHODS: One hundred eighteen patients diagnosed with moderate-to-severe OSA were randomized to receive therapeutic or subtherapeutic CPAP for 4 weeks. Of these, 84 had full 24 h-Holter monitoring data at baseline and follow-up. Weighted means of all QTc-intervals were analysed over 24 h, during four time-periods (12 pm-6 am, 6 am-12 am, 12 am-6 pm, 6 pm-12 pm) as well as during each individual hour. A two-sided P value <0.05 was considered to be of statistical significance. RESULTS: QTc-intervals at baseline [mean (SD) over 24 h 407.8 ms (36.6)] were highest from 6 pm-12 pm [411.7 ms (42.0)] and shortest from 6 am-12 am [405.4 ms (39.5)]. Overall 24 h CPAP treatment effect on QTc was -11.3 ms [95% confidence interval (CI), -22.1 to -0.6; P=0.039] and was estimated to be greater from 6 pm-12 pm than from 12 pm-6 am (P=0.068). The CPAP treatment effect on QTc was driven by those patients in the highest QTc decile at baseline (all >430 ms). In these patients, CPAP led to reductions in QTc, allowing reclassification into lower risk-associated values of QTc (<430 ms). CONCLUSIONS: In this exploratory study, CPAP treatment led to an overall reduction in the QTc-interval compared with subtherapeutic CPAP. This reduction seems more pronounced during evening hours and in patients with a QTc above 430 ms.