Brief Reports

Comparison of Tilt Angles and Provocative Agents (Edrophonium and Isoproterenol) to Improve Head-Upright Tilt-Table Testing

Head up tilt test is a well-known medical procedure used to diagnose vasovagal syncope. Several studies have focused on the early prediction of the outcomes of this test to predict syncope before its occurrence. Therefore, the evaluation of the dynamic interactions between several cardiovascular variables can play an important role to improve our understanding on the function of the baroreflex control of arterial blood pressure and can help to enhance the prediction performance. In this aim, the smoothed pseudo-Wigner–Ville distribution (SPWD) approach was used to characterize the time–frequency relationship between time series extracted from ECG (RR-interval) and blood pressure (amplitudes of the systolic blood pressure, the peak amplitude of the first derivative of the blood pressure, dP/dt and the variability of the pulse transit time, PTT). Two new indexes quantifying the relationship between time series were introduced. The first index computed the distribution of time–frequency coherence between 2 time series in different frequency bands and the second one computed the scalar product of the time–frequency spectra of these time series. This approach was applied to predict the outcome of a head up tilt test (HUTT) based on the first 15 min, to early detect subjects that would faint or not during this test. Our results demonstrate that the strongest parameter to predict HUTT result is the dynamic interaction between RR-interval and the amplitude of systolic blood pressure (AmpS), using the scalar product of the auto time–frequency spectra computed with SPWD (sensitivity: 87.5%; specificity: 93.8%). This study also shows that in high frequency band, the similarity between the RR-interval and the AmpS time series is higher during the first 15 min of HUTT in subjects that would faint. As a clinical viewpoint, these results could bring new perspectives to better understand physiological mechanisms during HUTT and syncope, which are still unclear and could lead also to a reduction of HUTT duration, which is currently between 30 and 45 min.

Vasovagal syncope (VVS) has been diagnosed with increasing frequency in older patients since the head-up tilt-table test (HUT) was described over 2 decades ago. The incidence and prevalence of VVS in this age group remains unknown. Older individuals are more likely to display a dysautonomic hemodynamic pattern with a predominantly hypotensive response during HUT. The positivity rates to passive and isoprotenerol-provoked HUT are reduced with age, but positivity rates for glyceryl-trinitrate-induced HUT are comparable with younger subjects. Few studies into treatment strategies have included older subjects. This is a review of the existing literature on the epidemiology, clinical characteristics, diagnostic tools, and treatment strategies for VVS in older patients, highlighting important areas for future research.

It is unknown if the head-upright tilt test in patients who receive isoproterenol and nitroglycerin can identify different populations with vasovagal syncope. The aim of this study was to compare the positive or negative responses to passive tilt between isoproterenol- and nitroglycerin-sensitized upright tilt. Ninety-six patients referred for unexplained recurrent syncope underwent passive tilt (45 minutes at 70° angle), which was then systematically followed, within the same session and in a random order, by a 20-minute tilt at a 70° angle after administration of nitroglycerin (NTG-tilt) and 10-minute tilt at a 70° angle with a continuous infusion of isoproterenol (ISO-tilt). NTG-tilt led to significantly more positive responses than passive tilt or ISO-tilt (55% vs 34% vs 42%, respectively). In the subgroup of patients with a positive response during passive tilt, the percentage of positive responses with NTG-tilt was significantly higher than with ISO-tilt (94% vs 67%). The agreement between NTG-tilt and ISO-tilt was very weak (Kappa coefficient 0.06). In the subgroup of patients with a negative response during passive tilt, the percentage of positive responses between NTG-tilt and ISO-tilt was similar (35% vs 29%). The agreement between NTG-tilt and ISO-tilt was good (Kappa coefficient 0.34). NTG-tilt led to a higher number of positive responses than ISO-tilt, especially when passive tilt outcome was positive. These 2 pharmacologic agents may identify 2 different subpopulations of patients because of their specific pharmacologic actions.