Circadian variation of cardiac autonomic nervous activity is well preserved in patients with mild to moderate chronic heart failure: effect of patient position

Background: It remains unclear whether circadian variation (CV) of cardiac autonomic nervous activity (CANA) is preserved in patients with chronic heart failure (CHF) as in healthy subjects. We have demonstrated that CANA in CHF patients is largely affected by patient recumbent position. Methods: We studied eight mild to moderate CHF patients and eight age, sex-matched healthy subjects. Each subject underwent 24-h ambulatory ECG monitoring. One channel was used to record the CM5 lead, and another to record the signal of patient position from a newly developed, small-sized detector. By using spectral analysis of heart rate variability, frequency-domain measures were calculated. Normalized high-frequency (HF: 0.15–0.40 Hz) power was used as an index of vagal activity and the low frequency (LF: 0.04–0.15 Hz)/HF power ratio was used as an index of sympathovagal balance. These indexes in the same recumbent position were compared between night (2:00–4:00 a.m.) and morning (6:00–8:00 a.m.). Results: In healthy subjects, a definite CV of CANA was observed in each recumbent position. In patients with CHF, in each position, normalized HF power was lower in the morning than at night, whereas LF/HF was higher in the morning than at night. Thus, CANA in CHF patients is influenced not only by patient position but also by the time of day. Conclusion: CV of CANA in mild to moderate CHF patients is well preserved when taking patient position into consideration.