Impact of Obstructive Sleep Apnea-Hypopnea Syndrome Severity on Heart Rate Variability and QTc Interval in Hypertensive Patients.

Background and Objectives: Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS) is associated with increased cardiovascular risk, particularly in hypertensive patients. Heart rate variability (HRV) and QTc interval are noninvasive markers of autonomic function and ventricular repolarization, respectively, but their relationship with OSAHS severity remains unclear. To investigate whether the severity of OSAHS influences standard HRV and QTc parameters in hypertensive patients with moderate or severe OSAHS. Materials and Methods: This prospective study included 110 hypertensive patients with moderate (AHI 15-29.9/h, n = 37) or severe (AHI ≥ 30/h, n = 73) OSAHS. All patients underwent full-night respiratory polygraphy and 24-h Holter ECG monitoring. HRV indices (SDNN, SDANN, SDNNi, RMSSD, SDSD) and QTc interval were analyzed. Associations with OSAHS parameters and nocturnal hypoxemia were assessed using partial correlation and multivariate models, adjusted for obesity, diabetes mellitus, metabolic syndrome, and beta-blocker use. Results: Patients with severe OSAHS had higher body weight and neck circumference, and a higher prevalence of diabetes and obesity compared to those with moderate OSAHS. HRV and QTc parameters did not differ significantly between groups. Notably, reduced SDNN was independently associated with the percentage of time spent with oxygen saturation below 90% (TST90%, p = 0.003) and mean oxygen saturation (p = 0.003), indicating autonomic imbalance. QTc prolongation (≥450 ms in men, ≥460 ms in women) was present in 9.6% of patients but was not directly related to OSAHS severity. Conclusions: Hypertensive patients with OSAHS have a high cardiovascular risk burden and frequent autonomic dysfunction. Nocturnal hypoxemia is independently associated with impaired HRV, reflecting sympathetic predominance. QTc prolongation appears to be influenced by additional comorbidities rather than OSAHS severity alone.