Influence of Menstrual Cycle on QT Interval Dynamics

OBJECTIVES: The aim of this study was to investigate the effects of the menstrual cycle on QT interval dynamics and the autonomic tone in healthy women. METHODS: Holter ECGs were recorded in 11 healthy women aged 18-32 years during the follicular and luteal phases of their regular menstrual cycle. The interval from QRS onset to the apex (QaT) and to the end of the T-wave (QeT), the interval between the apex and the end of the T-wave (Ta-e), and RR intervals were measured automatically in the course of 24 hours by Holter ECGs. The QeT/RR, QaT/RR, and Ta-e/RR relationships were evaluated in each subject. The autonomic tone was assessed by the serum catecholamine level at rest and heart rate variability was measured by Holter ECGs. RESULTS: (1) The follicular and luteal phases did not differ significantly with respect to the slopes of the QeT/RR, QaT/RR, and Ta-e/RR relationships. However, QeT and QaT intervals were significantly shorter for all RR intervals in the luteal than in the follicular phase (P < 0.0001). (2) The serum progesterone concentration was significantly higher in the luteal than in the follicular phase (P < 0.001). (3) Noradrenaline was significantly higher in the luteal than in the follicular phase (P < 0.05). There was no significant difference in the follicular and luteal phases with respect to heart rate variability measurements. CONCLUSIONS: Our results suggest that the menstrual cycle affects the QT intervals. The observed shorter QT interval during the luteal than the follicular phase may be attributable to the increase in serum progesterone and sympathetic tone.