Discussion
In this multi-center analysis of syncope patients with high pre-test probability of reflex mechanism, we found a characteristic hemodynamic pattern among those who were tilt-test positive. Tilt-positive patients had lower systolic and diastolic blood pressure and heart rate compared with tilt-negative patients. These differences were present among both males and females, although clinically small were highly statistically significant.
We sought a pathophysiological background for hypotensive susceptibility shown by a positive tilt test. It must be emphasized that we were not attempting to predict individual TT results. From our observations, we propose that patients prone to reflex syncope during orthostatic provocation differ hemodynamically from tilt-negative syncope patients. Tilt-test positive patients have narrower hemodynamic margins in the face of orthostatic stress and more compromised cardiac output, expressed by lower initial SBP, rendering their potential for less optimal compensation, also, contributing were lower heart rate and DBP. Consequently, we infer that there are two different hemodynamic patterns corresponding to two levels of hypotensive susceptibility, i.e. patients who may be susceptible to reflex syncope but are resistant to orthostatic stress thanks to well-functioning compensatory mechanisms, and those with a more pronounced hypotensive susceptibility who are prone to develop reflex syncope during TT. The latter with lower BP may compensate less efficiently than the tilt-negative syncope population. Thus, patients with higher BP and HR who are TT-negative may only sustain reflex syncope under clinically more adverse conditions than the more hypotensive susceptible TT-positive patients.