The main determinant of hypotension in nitroglycerine tilt-induced vasovagal syncope.
BACKGROUND
The aim of the study was to assess the main determinant of the fall in blood pressure (BP) responsible for the head-up tilt testing-induced syncope.


METHODS AND RESULTS
The study involved 200 patients (mean age 42 ± 3; 81 male) with syncope of unknown origin after the first evaluation. According to the response to the diagnostic tilt test, the population study was divided into four groups: Group I with mixed vasovagal syncope; Group II with cardioinhibitory syncope; Group III with vasodepressive syncope; Group IV: 40 patients with clinical syncope but no tilt-induced syncope. Finger arterial BP (Portapres, TNO, Amsterdam, the Netherlands) was recorded during tilt testing. Left ventricular stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) were computed from the pressure pulsations (Modelflow, TNO, Amsterdam, the Netherlands). During syncopal phase, the TPR decreased significantly in Group III, and increased in Group I and in Group II. CO decreased in Group I and in Group II and did not change significantly in Group III. SV decreased significantly in all groups.


CONCLUSIONS
Our data showed that the arterial system appears to be the main determinant of the BP fall in vasodepressive vasovagal syncope; while the impaired constrictive response of the venous system, leading to reduced venous return to the heart, appears to be the main determinant of BP fall in mixed and cardioinhibitory vasovagal syncope.