Effects of testosterone on the Q-T Interval in older men and older women with chronic heart failure

The Q-Tc interval duration on the electrocardiogram is recognized to differ between the sexes. In vitro data and data from humans before and after puberty and menopause suggest that sex hormones play a role in the longer Q-Tc intervals in women, or conversely, the shorter Q-Tc intervals in men. Direct investigations of sex hormone effects on the Q-Tc interval in humans, however, are limited and reach conflicting conclusions. Our objective was to determine effects of testosterone on ECG Q-T intervals of older men and older women. ECG's from 84 older men and older women in double-blind placebo-controlled investigations of testosterone supplementation for the treatment of chronic heart failure (CHF) were analysed. Thirty men received 1000mg intramuscular long-acting testosterone undecanoate and 28 men received saline at 0, 6 and 12weeks. ECG's were recorded at baseline and 12weeks. Sixteen women received transdermal testosterone (33μg) and 10 women received matching placebo twice weekly for 24 weeks with ECG's at baseline and after 24weeks. Testosterone, but not placebo, shortened Q-T and Q-Tc intervals without heart rate changes. Q-T intervals decreased from 385±28 (mean±SD) to 382±28 ms (p<0.002) and Q-Tc intervals decreased from 398±26 to 392±27 (p<0.006) in men on testosterone. In women, Q-T intervals decreased from 400±25 to 397±23ms (p=0.06) and Q-Tc intervals from 415±26 to 409±27ms (p=0.3) on testosterone. Q-T intervals were longer in women compared with men under all conditions (p<0.03). The data support a direct effect of testosterone to shorten Q-T intervals in older men and older women in the absence of HR changes or hypogonadal status. Mean decreases are small and unlikely to affect risks of arrhythmic events in patients receiving Q-T prolonging medications.