Hashimoto K, et al. - Using 24-hr ambulatory electrocardiogram (AECG), frequency domain (FD)-T-wave alternans (TWA) analysis was conducted in 47 subjects without significant structural heart disease, the researchers intended to understand if TWA is affected by heart rate (HR) or cardiac autonomic nervous activity. The diurnal variation of FD-TWA was observed. While there was a negative correlation between FD-TWA and HFnu, positive correlations among maximum FD-TWA and HR and LF/HF were observed. An independent effect of HR on log FD-TWA amplitude was also noticed. Hence, in the daily life of the subjects without significant structural heart disease, FD-TWA showed a considerable diurnal variation which could be more powerfully affected by HR in comparison to the HRV indices.