ABSTRACT Study Objectives Single‐night polysomnography assumes stable sleep apnoea (SA) severity; night‐to‐night variability may identify clinically relevant phenotypes, particularly in women. Sex/gender‐specific longitudinal phenotypes were characterised using device‐detected respiratory disturbance index (RDI) and an instability metric independent of mean severity. Methods Pacemaker patients in the prospective ACaSA study with at least 180 valid nightly RDI measurements after a 30‐day post‐implant period were analysed. Severity was summarised by mean RDI. Variability was summarised by an Instability Index (residual from the log–log regression of RDI standard deviation on mean RDI). Phenotypes were defined by mean RDI (< 20 vs. ≥ 20 events/h) and instability (above vs. below median). Results About 37,260 nights from 207 patients (median age 76 years, IQR 69–81) were analysed. Four phenotypes were identified: Mild ‐ Stable ( n = 68), Mild ‐ Unstable ( n = 67), Severe ‐ Stable ( n = 35), and Severe ‐ Unstable ( n = 37). Women comprised 37.7% of the total cohort and they were disproportionately overrepresented in the Mild ‐ Unstable versus in the Mild ‐ Stable phenotype (61.2% vs. 33.8%; p = 0.002). Among patients with mean RDI < 20 ( n = 135), female sex/gender (adjusted OR 3.38, 95% CI 1.60–7.40; p = 0.002) and obesity (BMI ≥ 30 kg/m 2 ; adjusted OR 3.80, 95% CI 1.31–12.53; p = 0.019) were independent predictors of the Mild ‐ Unstable phenotype. Mild‐Unstable had more severe‐range nights (RDI ≥ 20/h) than Mild‐Stable (7.8% vs. 2.2%; p < 0.001). Severe‐Unstable recorded RDI < 20/h on 33.9% of nights versus 13.9% in Severe‐Stable ( p < 0.001). Conclusion Night‐to‐night variability identifies longitudinal SA phenotypes not captured by mean RDI. A female‐ and obesity‐predominant Mild ‐ Unstable phenotype shows intermittent severe‐range nights despite low average burden, while instability in severe SA increases the likelihood of underestimating severity when classification is based on a single‐night test.
Spitaler et al. (Fri,) studied this question.