Age- and gender-related differences in QTc-interval are most likely the result of changes in sex-specific hormones. Although the exact mechanisms and pathophysiology of sex hormones on the QTc-interval are not known, testosterone appears to shorten the QTc-interval. In females, however, there is a more complex interaction between progesterone and estrogen. In patients with an impaired repolarization, such as long-QT syndrome (LQTS), the effect of these sex hormones on the QTc-interval is more pronounced with a differing sensitivity between the LQTS genotypes.
Vink, A. S., Clur, S-A. B., Wilde, A. A. M., & Blom, N. A. (2018). Effect of age and gender on the QTc-interval in healthy individuals and patients with long-QT syndrome. Trends in cardiovascular medicine, 28(1), 64-75. https://doi.org/10.1016/j.tcm.2017.07.012