Influence of Normal Menstrual Cycle on
Autonomic Nervous Activity and QT Dispersion

Machiko Yamamoto^a, Yumiko Tsutsumi^b, Kaori Furukawa^a, Yuki Kanno^a,
Ryoko Maruyama^a, Hiroshi Satoh^b

^aSchool of Nursing, Miyagi University, Sendai, Japan
^bThe Cardiovascular Institute, Tokyo, Japan

Correspondence: Machiko Yamamoto, School of Nursing, Miyagi University, 1-1 Gakuen, Taiwa-cho, Miyagi 981-3271 Japan.
E-mail: yamamoto@my.ac.jp, phone +81-22-377-8257, fax +81-22-377-8257

1.  Introduction

The reduction in estrogen levels experienced by postmenopausal women is known to be a cause of ischemic heart disease and cardiac sudden death. However, the effects of estrogen have not been clarified. We studied the changes in autonomic nervous activity (ANA) and QT dispersion (QTD) that occurred during the normal menstrual cycle of healthy young women.

2.  Subjects and Methods

We studied the changes in ANA and QTD that occurred during the normal menstrual cycle of 12 healthy young women (mean age 20.8 years). Continuous ECG and blood pressure (BP) were monitored during the follicular phase (F-phase) and luteal phase (L-phase). ANA was evaluated by heart rate variability (HRV) and baroreflex sensitivity (BRS). HRV was assessed by CGSA. BRS was measured using the sequential method. QTc and QTD were measured using a standard 12-lead ECG.

3.  Results

Results are shown in Table 1. Heart rate (HR) and SBP were significantly higher in the L-phase than in the F-phase. In the F-phase, HF and BRS were significantly higher than in the L-phase (HF 901±451 vs. 602±293 ms, p=0.01; BRS 36.7±9.3 vs. 29.3±8.7 ms/mmHg, p=0.009) and LF/HF was tended to be higher in the L-phase. Although QTc remained unchanged, QTD was extended during the L-phase (38.7±13.6 vs. 56.2±9.8 ms, p=0.0005).

Table 4.    L-phase vs F-phase.

4.  Conclusion

In conclusion, parasympathetic activity decreases and sympathetic activity increases during the L-phase of the normal menstrual cycle. QTD extension may reveal increased variation in the repolarization process in the ventricle. These findings may suggest the increased incidence of cardiac sudden death and cardiovascular disease in postmenopausal women.