Effects of long-term hormone replacement therapy on QT and corrected QT dispersion during resting and peak exercise electrocardiography in post-menopausal women.

It is known that the QT interval is longer in women than men. Estrogen is reported to account for the QT interval prolongation in several studies conducted with hormone replacement therapy (HRT) in postmenopausal women. Along with this, there are conflicting data as regards the effects of HRT on QT interval and dispersion. Moreover, there is no evidence about the effect of HRT on exercise QT parameters. We compared QT parameters obtained from surface electrocardiograms during resting and peak exercise before and after 6 months of HRT consisting of estrogen plus progesterone in healthy postmenopausal women. Twenty-four healthy postmenopausal women were given 0.625 mg/day conjugated estrogens and 2.5 mg/day medroxyprogesterone acetate for 6 months. Exercise stress testing using the Bruce protocol was performed before and after HRT. QT maximum, minimum, dispersion and corrected QT maximum, minimum and dispersion were calculated during resting and peak exercise. HRT resulted in a significant increase in estradiol plasma levels from 24+/-10 pg/mL to 117+/-66 pg/mL (P<0.001). There was no significant difference in resting QT parameters after HRT, whereas QT dispersion and corrected QT dispersion were significantly increased during peak exercise (20+/-7 versus 25+/-10 ms; P<0.05, 33+/-12 versus 41+/-16 ms; P<0.05, respectively). Nonetheless, the other exercise QT parameters were unchanged. The resting QT parameters are not affected by long term HRT consisting of estrogen plus progesterone, which leads to an increase in QT dispersion and corrected QT dispersion during peak exercise.