Women have a higher incidence than men of torsades de pointes ventricular
arrhythmias after administration of drugs that prolong cardiac repolarization.
Although the QT interval does not vary during the menstrual cycle in the absence
of drugs, Rodriguez and colleagues report that mean QT prolongation after
administration of ibutilide, an antiarrhythmic agent, was greater for women
during menses and the ovulatory phase compared with women during the luteal
phase or with men.