A Higher Proportion of Men Than of Women Fainted in the Phase Without Nitroglycerin in Tilt-Induced Vasovagal Syncope.

Vasovagal syncope (VVS) affects more women than men. We determined whether this sex ratio affects tilt table test (TTT) results. We retrospectively studied TTT outcomes in suspected VVS. TTT consisted of supine rest, a maximum 20 min of head-up tilt without and, if nitroglycerin was needed, a further maximum 20 min after nitroglycerin administration. TTT was terminated if VVS occurred. We used binary logistic regression for the entire TTT and for each phase, with VVS as outcome and age and sex as predictors. TTT provoked vasovagal (pre)syncope in 494 out of 766 tests (64%). The proportion of men and women who fainted during the entire TTT did not differ significantly between the sexes (p = 0.13, corrected for age). A lower proportion of women than men had VVS in the phase without nitroglycerin (odds ratio 0.54; 95% confidence interval 0.37–0.79; p = 0.002, corrected for age), whereas a higher proportion of women than men fainted after nitroglycerin (odds ratio 1.58; 95% confidence interval 1.13–2.21; p = 0.008, corrected for age). These sex differences remained significant after correction for a history of orthostatic versus emotional triggers. The effect of sex on TTT outcome was closely associated with differences of blood pressure change upon tilt-up (lower in men in both TTT phases: without nitroglycerin p = 0.003; with nitroglycerin p = 0.05), but not with heart rate changes. Men were more susceptible to induction of VVS without nitroglycerin and women after it. The unexpected findings may be due to sex-specific pathophysiological differences.