gms | German Medical Science

The reduction in estrogen levels experienced by postmenopausal women is known to be a cause of ischemic heart disease and sudden cardiac death. And also, the balance of autonomic nervous activity (ANA) in early morning has been postulated as a sign of the prognosis, reflecting increased incidences of sudden death in patients with cardiovascular diseases. We studied the changes in circadian rhythm of ANA that occurred during the normal menstrual cycle of 3 healthy young women (mean age 21.5 years). Holter ECG was monitored during the follicular phase (F-phase) and luteal phase (L-phase). ANA was evaluated by heart rate variability (HRV). The total heart beats/24hrs increased during L-phase, and SDNN/24hrs and CVRR/24hrs reduced during L-phase in all 3 cases. While HR every an hour, high frequency spectra (HF) and low frequency spectra (LF)/HF demonstrated typical circadian rhythm. However, early morning HR during L-phase was significantly higher than that during F-phase (Figure-1) in all 3 cases. HF decreased and LF/HF slowly increased during F-phase. These findings suggest possible basis, at least, for the increased incidence of sudden cardiac death and cardiovascular disease in postmenopausal women, and also high incidences occurring in early morning.