Autonomic nervous system activity in idiopathic dilated cardiomyopathy and in hypertrophic cardiomyopathy.

To assess autonomic nervous activity in patients with cardiomyopathies, analysis of heart rate variability was performed using 24-hour ambulatory electrocardiograms in 14 patients with idiopathic dilated cardiomyopathy (IDC), 15 with hypertrophic cardiomyopathy (HC) and 18 healthy subjects. Heart rate variability during the night and daytime was calculated using fast-Fourier transform, and power spectra were quantified in 2 frequency bandwidths: 0.00 to 0.15 Hz (low-frequency power [LF]) and 0.15 to 0.50 Hz (high-frequency power [HF]). Log(HF) was used as an index of parasympathetic nervous activity, and log(LF/HF), of sympathetic nervous activity. Log(HF) was significantly lower and log(LF/HF) was significantly higher in IDC. These changes were related to ejection fraction. In HC, lower log(HF) and higher log(LF/HF) were recognized only during the night, and these changes were independent of the degree of myocardial hypertrophy. Our results indicated attenuation of parasympathetic activity and enhanced sympathetic activity in HC during the night, and also in IDC. Assessment of autonomic imbalance by analysis of heart rate variability may be useful for understanding the pathophysiology of cardiomyopathies.