title: Modulations of autonomic activity leading to tilt-mediated syncope.
abstract: BACKGROUND
  Vasovagal syncope (VVS) results from a complex interaction among afferent vagal and sympathetic signals, cortical modulation and bulbar integration. The aim of our study was to evaluate the modifications of autonomic activity during Upright Tilt Test (UTT) in patients with unexplained syncope, and to correlate these changes with the specific cardiovascular reactions induced.
  
  
  RESULTS
  We studied 90 patients with a mean age of 44+/-17 yrs. Frequency domain analysis of heart rate variability (HRV) (normalized units) was performed on 2 periods of 300 beats: at baseline and after 5 min of 60 degrees tilt. UTT was positive in 56 patients (62%). The responses were cardioinhibitory in 8, vasodepressive in 15, mixed in 33. Baseline LF and HF components did not show significant difference between subjects with positive or negative test (HF: 39+/-21 versus 41+/-22; LF: 50+/-22 versus 49+/-23). HRV during UTT showed similar changes in patients with positive or negative test. However, subjects with mixed or cardioinhibitory reactions were characterized by a relevant increase of LF during UTT (from 47+/-23 to 66+/-21), whereas the others by a non-significant decrease of the same component (from 57+/-19 to 51+/-31).
  
  
  CONCLUSIONS
  Patients developing a reflex cardioinhibitory reaction during UTT were characterized by an increase of sympathetic activity during the test, that might represent an essential factor to induce a stronger vagal reaction on the sinus node. On the contrary, in subjects with vasodepressive reactions an inadequate enhancement of the sympathetic drive, probably causing a failure of peripheral vasoconstriction, was evidenced.
authors.affiliation: Department of Cardiology, Via Giustiniani, 2, 35128 Padova, Italy. franco.folino@unipd.it
authors.forename: Antonio Franco
authors.initials: AF
authors.lastname: Folino
authors.forename: Giulia
authors.initials: G
authors.lastname: Russo
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Buja
authors.forename: Sergio
authors.initials: S
authors.lastname: Cerutti
authors.forename: Sabino
authors.initials: S
authors.lastname: Iliceto
mesh_terms: D000328:Adult; D000367:Age Factors; D001341:Autonomic Nervous System / Q000503:physiopathology*; D017704:Baroreflex / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D016683:Supine Position; D019462:Syncope, Vasovagal / Q000209:etiology / Q000503:physiopathology*; D018667:Tilt-Table Test