Twenty-four-hour spectral analysis of heart rate variability in congestive heart failure secondary to coronary artery disease

It is well known that heart rate (HR) fluctuates in time and that this variation is closely related to changes in the neural activity to the heart.^1,2 Therefore, HR variability represents a noninvasive parameter for studying the autonomic control to the heart. Recently, it has been shown that HR variability is a powerful independent prognostic factor in patients with coronary artery disease³ and a low HR variability count has been found to be related to sudden death.⁴ Spectrum analysis of HR may provide further information, since HR variability possesses 2 major components that have been shown to relate to different patterns of neural control to the heart.^5,6 Patients with congestive heart failure (CHF) have a complex abnormality of the autonomic control to the heart⁷ that also affects some HR characteristics.⁸ These abnormalities may be determined either by a selective reduction of the vagal outflow to the heart or by a more complex abnormality. This investigation was undertaken to evaluate the components of HR variability in normal persons and patients with CHF, and their 24-hour behavior.