Nocturnal hypoxemic burden in patients with heart failure: Emerging prognostic role of its nonspecific component.

Background: Nocturnal hypoxemic burden has been shown to be a robust, independent predictor of all-cause mortality in patients with heart failure and reduced ejection fraction (HFrEF) and to occur in a severe form even in patients with low or negligible frequency of respiratory events (apneas/hypopneas). This suggests the existence of two components of hypoxemic burden: one unrelated to respiratory events and the other related. The aim of this study was to characterize these two components and to evaluate their prognostic value.

Methods: Nocturnal hypoxemic burden was assessed in a cohort of 280 patients with HFrEF by measuring the percentage of sleep with an oxygen saturation (SpO) <90% (T90), and the area of the SpO curve below 90% (Area90). Both indices were also recalculated within the sleep segments associated with respiratory events (event-related component: T90, Area90) and outside these segments (nonspecific component: T90, Area90). The outcome of the survival analysis (Cox regression) was all-cause mortality.

Results: During a median follow-up of 60 months, 87 patients died. T90, Area90, and their components were significant in univariate analysis (P < .05 all). However, when these indices were adjusted for known risk factors, T90, T90, Area90, and Area90 remained statistically significant (P = .018, hazard ratio (HR)=1.12, 95%CI=(1.02, 1.23); P = .007, HR=1.20, 95% CI = [1.05, 1.37]; P = .020, HR = 1.05, 95% CI = [1.01, 1.10]; P = .0006, HR = 1.15, 95% CI = [1.06, 1.25]), whereas T90 and Area90 did not (P = .27, P = .28). These results were internally validated using bootstrap resampling.

Conclusions: By demonstrating a significant independent association of nonspecific hypoxemic burden with all-cause mortality, this study suggests that this component of total nocturnal hypoxemic burden may play an important prognostic role in patients with HFrEF.