Time-frequency decomposition of HR and BP variability in reflex syncope

Autonomic control plays an essential role in the pathogenesis of reflex syncope. However, the precise etiology of syncope is still not completely understood and the clinical diagnosis of its origin remains rough and empirical. The Head Up Tilt (HUT) test is used to reproduce symptoms. The authors have applied time frequency decomposition of HRV and BPV, which allows them to evaluate the exact time evolution of the autonomic activity even during the transient stages of the HUT and syncope. The authors have observed in typical vasovagal syncope the sympathetic withdrawal and the subsequent vagal surge. They have also been able to show that no vagal surge occurs at the instant of vasodepressor syncope. They have observed that the vagal activity is enhanced and the sympathovagal balance is lower in the tilted position among subjects with positive HUT as compared to negative HUT.