Changes in Cardiac Autonomic Control During Nocturnal Repetitive Oxygen Desaturation Episodes in Patients with Coronary Artery Disease

Abstract

Periodic fluctuations in respiration such as Cheyne-Stokes respiration or the sleep apnoea syndrome are known to be associated with very-low-frequency oscillations in heart rate (cycle times about 30-120s), which may be related to periodic changes in sympathetic and vagal tone. Since disturbances in cardiac sympathovagal balance have been associated with increased cardiovascular morbidity and mortality, especially in patients with coronary artery disease (CAD), we investigated changes in cardiac autonomic control in patients with CAD during periodic breathing episodes. Thirty-five patients with a left ventricular ejection fraction (LVEF) of > 50% and 13 patients with an LVEF of < or = 35%, who were scheduled for coronary bypass surgery, were studied using a nocturnal Holter electrocardiograph (ECG) and pulse oximetric recordings. Heart rate variability was assessed by spectral analysis during cyclic oxygen desaturation episodes, indicating periodic breathing patterns, and during control episodes with normal oxygen saturation. Cyclic oxygen desaturation episodes with a duration of at least 20 min were observed in 17 patients with an LVEF of > 50% and in nine patients with an LVEF of < or = 35% (minimal oxygen saturation 83.9 +/- 3.1 versus 80.4 +/- 5.6%; cycle frequency between 0.0068 and 0.0294 Hz, no significant differences between groups), all of which were associated with very-low-frequency (0.0033-0.04 Hz) oscillations in the heart rate. During cyclic desaturation episodes patients with normal, as well as those with imparied left ventricular function, had marked increases (P < 0.01) in very low frequency power, low frequency (0.04-0.15 Hz) power and the ratio of low-to-high frequency (0.15-0.4 Hz) power. The low:high frequency ratio was significantly higher in patients with an LVEF of > 50% than in patients with an LVEF of < or = 35% during cyclic desaturation episodes, but not during control episodes. Repetitive oxygen desaturation episodes are associated with marked changes in heart rate variability which indicate cardiac sympathetic predominance in patients with CAD. Our results suggest differences in the modulation of cardiac sympathovagal balance during periodic breathing episodes between patients with normal and imparied left ventricular function.