title: Enhanced reflex response to baroreceptor deactivation in subjects with tilt-induced syncope.
abstract: 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.
authors.affiliation: Institute of Cardiology, University of Bari, Italy. mariavittoria.pitzalis@cardio.univa.it
authors.forename: Mariavittoria
authors.initials: M
authors.lastname: Pitzalis
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Parati
authors.forename: Francesco
authors.initials: F
authors.lastname: Massari
authors.forename: Pietro
authors.initials: P
authors.lastname: Guida
authors.forename: Marco
authors.initials: M
authors.lastname: Di Rienzo
authors.forename: Brian
authors.initials: B
authors.lastname: Rizzon
authors.forename: Paolo
authors.initials: P
authors.lastname: Castiglioni
authors.forename: Massimo
authors.initials: M
authors.lastname: Iacoviello
authors.forename: Filippo
authors.initials: F
authors.lastname: Mastropasqua
authors.forename: Paolo
authors.initials: P
authors.lastname: Rizzon
mesh_terms: 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