Enhanced reflex response to baroreceptor deactivation in subjects with tilt-induced syncope.
OBJECTIVE
We sought to evaluate whether changes in resting baroreflex control of heart rate are a distinctive feature of healthy subjects with a history of syncope prone to a positive tilt-test response.


BACKGROUND
The mechanisms involved in the pathogenesis of vasovagal syncope (VVS) are still poorly understood; in particular, the contribution of arterial baroreflex control of heart rate is matter of discussion.


METHODS
A passive tilt-table test was performed in 312 consecutive, otherwise healthy subjects (age 36 +/- 15 years) with unexplained syncope and 100 control subjects. At baseline, spontaneous baroreflex sensitivity (BRS; ms/mm Hg) and the baroreflex effectiveness index (BEI) were assessed using the sequence method.


RESULTS
The study population showed normal baroreflex function. Tilt-induced VVS in 94 subjects who were younger than both the tilt-negative and control subjects (30 +/- 14, 38 +/- 15, and 37 +/- 14 years, respectively; p = 0.00005) showed greater BRS (17.4 +/- 9.8, 13.2 +/- 7.9, and 12.8 +/- 8.2 ms/mm Hg, respectively; p = 0.0001), but had a similar BEI (0.59 +/- 0.18, 0.56 +/- 0.19, and 0.58 +/- 0.2, respectively; p = NS). On Cox multivariate analysis, the occurrence of VVS during tilt was inversely related to age (hazard ratio 0.97; p = 0.0004) and directly related to the BRS slope of sequences, implying a baroreceptor deactivation (hazard ratio 1.05; p = 0.02), but not of sequences characterized by arterial baroreceptor stimulation.


CONCLUSIONS
Subjects with tilt-induced VVS showed greater resting BRS but had a normal BEI. The enhanced reflex tachycardic response to arterial baroreceptor deactivation at rest may represent a characteristic feature of subjects prone to tilt-induced VVS.
Pitzalis
Mariavittoria
M
Institute of Cardiology, University of Bari, Italy. mariavittoria.pitzalis@cardio.univa.it
Parati
Gianfranco
G
Massari
Francesco
F
Guida
Pietro
P
Di Rienzo
Marco
M
Rizzon
Brian
B
Castiglioni
Paolo
P
Iacoviello
Massimo
M
Mastropasqua
Filippo
F
Rizzon
Paolo
P
D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D015999:Multivariate Analysis; D016016:Proportional Hazards Models; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D013610:Tachycardia / Q000503:physiopathology; D018667:Tilt-Table Test