Nocturnal Frequency Instability of Respiratory Sinus Arrhythmia in Heart Failure

In heart failure, early detection of exacerbation is required to avoid unnecessary hospitalization. Although respiration instability detected by a respiration sensor attached to the bed at home has been proposed, detection by a more popular general sensor is desired. Using the fact that the frequency of respiratory sinus arrhythmia (FRSA) reflects the frequency of breathing (FB), we developed a method to estimate the instability of FB by analyzing the instability of FRSA only using R-R interval time series obtained from nighttime ECG. In 69 healthy control subjects, the fluctuation of FRSA reduced to 6.8 ±3.9% of local mean during sleep, while it remained 16.4±7.7% and 17.5 ±5.8% in sinus rhythm patients with heart failure who survived for 38-mo follow-up period after recording (n = 52) and those died during the follow-up (n=29), respectively. FRSA instability detected by ECG during sleep may be used as a feature to screen patients with heart failure.