Correlation of heart rate variability with ST changes during 24 hour Holter monitoring

Heart rate variability (HRV), which is related to the activity of the automatic nervous system, was monitored during 24-h Holter recordings in 26 normal subjects. The power spectrum (PS) was obtained and the fluctuations in heart rate in three frequency bands were correlated with ST segment changes. Significant variations in HRV and ST segment amplitude were found during the night. ST level and the power of the HRV in the low- (0-0.05 Hz) and high- (0.2-0.35 Hz) frequency bands were increased significantly during the night in the majority of the subjects. The PS in the mid- (0.05-0.2 Hz) frequency range was significantly reduced at night. The heart rate and its global variability also decreased significantly during the night. The nocturnal changes in the PS in the low-frequency band and in the ST level may be related to alterations of the autonomic nervous system