HEART-RATE-VARIABILITY AND VENTRICULAR ARRHYTHMIA IN CLINICALLY STABLE PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY

To investigate whether autonomic nervous dysfunction exists and to det ermine the relationship between autonomic nervous activity and ventric ular arrhythmias in clinically stable patients with hypertrophic cardi omyopathy (HCM), we studied heart rate variability (HRV) in 21 patient s with HCM and 10 age-matched healthy control subjects. Patients were divided into 2 groups: HCM I (14 patients without nonsustained ventric ular tachycardia, defined as 3 or more consecutive ventricular prematu re beats) and HCM II (7 patients with nonsustained ventricular tachyca rdia). HRV was measured on 24-h ECG monitorings using both non-spectra l and spectral methods (fast Fourier transform, FFT). We assessed auto nomic nervous activity based on high-frequency (HF; 0.15-0.40 Hz, an i ndex of parasympathetic nervous activity) and the low-to high-frequenc y power ratio (LM ratio; an index of sympathetic nervous activity) dur ing daytime and night-time separately. There were no significant diffe rences in any index of HRV between the HCM I and control groups. HF in the HCM II group was significantly lower than that of both the HCM I and control groups during the day and at night, whereas the L/H ratio at night-time was significantly higher in the HCM II group than in the HCM I and control groups. These data demonstrate that, in clinically stable HCM patients without nonsustained ventricular tachycardia, auto nomic nervous activity was not different to that of healthy control su bjects, whereas in HCM patients with nonsustained ventricular tachycar dia, parasympathetic nervous activity was reduced throughout the 24-h period, and sympathetic nervous activity at night was increased compar ed with healthy control subjects. Thus, HCM patients with nonsustained ventricular tachycardia have to be treated even if they do not exhibi t significant clinical manifestation.