SAT413 Feminising Gender Affirming Hormone Therapy Prolongs QTc Interval

Disclosure: L. Angus: Speaker; Self; Kirin Brewery. T. Lin: None. S. Leemaqz: None. M. Grossmann: None. J.D. Zajac: None. A.S. Cheung: None. Background: In trans people using feminising hormone therapy there is an increased risk of cardiovascular events including conduction disorders. It is known that the QTc interval is longer in cisgender women of reproductive age than cisgender men, attributed to factors including serum sex steroid concentrations. Androgen deprivation therapy in men with prostate cancer is associated with prolongation of the QTc interval, but the effects of feminising hormone therapy in trans women are unclear. Methods: We measured the automated QTc interval from a 12-lead electrocardiogram at baseline and 6 months in trans women newly commencing feminising hormone therapy. Sex steroid concentrations were measured by LCMS. Participants were part of a randomised controlled double-blind trial of spironolactone 100mg daily versus cyproterone acetate 12.5mg daily in transgender women commencing estradiol for feminisation (ANZCTR 12620000339954) and this was a prespecified secondary outcome. Statistical analysis was performed using a linear mixed effects model looking at the effects of treatment over time. Results: Sixty-three participants were randomised and 55 participants completed the trial and were included in analysis (spironolactone group n=27, cyproterone acetate group n=28). Baseline group characteristics were comparable. Overall, the QTc interval increased by 18ms (95% CI 14 - 23 ms; p<0.001) at 6 months compared to baseline, but there was no between group difference (p=0.23). One participant had a QTc interval above 450ms. The mean serum total testosterone concentrations were similar between groups at baseline (spironolactone group 16.9 (13.5 - 20.3) nmol/L vs cyproterone acetate group 18.0 (15.0 - 21.0) nmol/L, p=0.60) but higher in the spironolactone group 4.3 (2.0 - 6.5) nmol/L than the cyproterone acetate group 1.5 (0.0 - 2.9) nmol/L, p<0.05 at 6 months. The mean serum estradiol and serum potassium concentrations were similar between groups at baseline and 6 months. Conclusions: Feminising hormone therapy with estradiol and either spironolactone or cyproterone acetate in trans women is associated with prolongation of the QTc interval over a six-month period. Further research is required to investigate the incidence of cardiac arrhythmia in this population. Presentation: Saturday, June 17, 2023