(P129) OVULATORY AND ANOVULATORY CYCLE PHASE INFLUENCES ON QT INTERVAL DYNAMICS DURING MENSTRUAL CYCLES

Background: Ovarian steroids during the menstrual cycle play a significant role in cardiac health. Although exogenous estrogen has been shown to lengthen the QT interval, progesterone may have the opposite effect. This study investigated the within-cycle influences of menstrual hormones during cycle phases on QT dynamics, comparing documented ovulatory with anovulatory cycles (having no increase in progesterone levels).

METHODS AND RESULTS: This prospective cohort investigation, a cardiac sub-study of the Menstruation and Ovulation Study 2 (MOS2), involved 62 healthy, regularly menstruating community-dwelling women during spontaneous menstrual cycles. Electrocardiographic recordings within-woman were obtained during the mid-follicular and the luteal or premenstrual phases (of anovulatory) cycle as documented by the validated Quantitative Basal Temperature© (QBT©) method. The Fridericia’s formula was used to rate-correct the QT interval (QTc). We also conducted a meta-analysis, integrating data from three additional ovulation-documented studies, to evaluate QTc changes across ovulatory menstrual cycles.

In the 26 ovulatory cycles, there was no significant change in QTc from mid-follicular to the luteal phases (383.0 ¬± 12.8 vs 382.6 ¬± 12.8 msec, P = .859). QTc, in the 36 anovulatory cycles, tended to increase from the mid-follicular to the premenstrual phase (381.7 ¬± 13.1 vs 385.0 ¬± 16.1 msec, P = .166). The 26 ovulatory cycles include not only those with normal luteal phase lengths (≥10 days) but also with short luteal phases ( < 10 days) that have lower progesterone production. Our meta-analysis yielded a random-effects weighted mean QTc shortening trend across the follicular-luteal phases, with a 1.67 msec shorter luteal phase (P =.53) that reflected the QTc change pattern observed in this primary study.

Conclusion: In a usual menstrual cycle, follicular phase QTc lengthening is attributed to the predominant presence of estradiol, and QTc shortening during the luteal phase is primarily driven by progesterone exerting a dominant effect over estrogen. The QTc tendency to prolong during an anovulatory cycle is likely related to longer exposure to estrogen without luteal phase progesterone “interference”. Additional research is needed to further investigate the effects of menstrual cycle hormonal fluctuations and their varying exposure durations on cardiac electrophysiology.