The Effect of Estrogen Replacement Therapy on Ventricular Repolarization Dynamics in Healthy Postmenopausal Women Bojan Vrtovec, MD, PhD, Vito Starc, MD, PhD, and Helena Meden-Vrtovec, MD, PhD Abstract: Even though gender-specific differences in ventricular repolariza- tion have gained wide recognition, the underlying mechanisms remain un- known. Because estrogen hormones may represent a causative factor for the changes in ventricular repolarization in women, this study evaluates a poten- tial impact of estrogen replacement therapy on ventricular repolarization dynamics. Beat-to-beat QT and RR interval variability and QT/RR relationship during 5 minute resting high-resolution electrocardiogram recordings were measured in 30 healthy postmenopausal women (mean age 54.5 years) before and after 10 weeks of estrogen replacement therapy (ERT) with estradiol 2 mg/day. The 2 control groups included 12 healthy postmenopausal women of the similar age, who did not receive ERT, and 11 comparably healthy age-matched men. To evaluate ventricular repolarization dynamics, QT/RR linear regression slopes were calculated. After the 10-week period, the QT/RR regression slope increased by 93% in the ERT group (P  .001), but no alterations were noted in either the male or female controls. The overall variability of RR and QT intervals did not change in any of the groups studied. Our results suggest that ERT causes alterations in ventricular repolarization dynamics without significantly affecting the autonomic nervous tone. Key words: Estrogen replacement therapy, ventricular repolarization dynamics, beat-to-beat QT interval variability. Changes in ventricular repolarization are increas- ingly often associated with ventricular arrhythmias and may therefore represent an important risk factor for sudden cardiac death (1,2). Drug-induced prolongation of ventricular repolarization is among the best known factors leading to polymorphic ventricular tachycardia (3). Women have been shown to have a significantly higher incidence of torsades de pointes compared to men,(4) suggesting a gender-related impact on ventricular arryhthmo- genesis. A connection between female gender and ven- tricular repolarization parameters has been ac- knowledged since 1920, when Bazett first described From the Institute of Physiology; and Division of Obstetrics and Gynecology, Ljubljana University Medical Center, Ljubljana, Slovenia. Reprint requests: Bojan Vrtovec, MD, PhD, Institute of Phys- iology, Ljubljana University School of Medicine, Zaloska 4, 1105 Ljubljana, Slovenia; e-mail: bojan.vrtovec@siol.net. Copyright © 2001 by Churchill Livingstone ® 0022-0736/01/3404-0001$35.00/0 doi:10.1054/jelc.2001.26323 Journal of Electrocardiology Vol. 34 No. 4 2001 277