High-resolution time-frequency characteristics of slower frequency heart rate variability in patients of chronic refractory congestive heart failure - the implications of beta-blocker therapy

The slower frequency range of heart rate variability (HRV) is seldom investigated in the clinical cardiovascular studies, owing to the lack of apparent physiological implication and the difficulty of spectral analysis. However, the distortion in HRV interpretation is exaggerated in congestive heart failure, which has marked sympathovagal imbalance. Utilizing the high-resolution smoothed pseudo Wigner-Ville distribution (SPWVD) in the analysis of frequency components below 0.07Hz, we studied the 24-hour HRV in 12 normal subjects, and 11 patients of chronic refractory congestive heart failure before and 3 months after the beta-blocker therapy. Low-dose atenolol resulted in apparent improvement of the cardiac functional class in all 11 patients. Before the beta-blocker, the SPWVD of the slower frequency HRV in heart failure patients was shown to have the unique long-wavelength (Cheyne-Stokes) oscillations between 0.008Hz and 0.025 Hz in 7 patients, as well as the generalized depression and loss of the diurnal change in 11 patients, contrasting to that of normal subjects. The beta-blocker therapy effectively reserved most of the abnormal phenomena, including the suppression of the Cheyne-Stokes oscillations and the resumption of the morning surge of HRV. Multiple frequency components of the slower frequency range were directly correlated to the cardiac performance manifested by the end-systolic, end-diastolic dimensions, fractional shortening and ejection fraction of the left ventricle. In conclusion, the slower frequency HRV in congestive heart failure could be representative of the pathophysiological signals of the internal milieu derangement.