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.