title: Evaluation of autonomic influences on QT dispersion using the head-up tilt test in healthy subjects.
abstract: Our objective was to examine the autonomic influence on QT interval dispersion using the head-up tilt test in healthy subjects. RR and QT intervals, heart rate variability, and plasma norepinephrine concentration were measured in the supine position and tilting to 70 degrees for 20 minutes using a footboard support in 15 healthy male volunteers (mean age +/- SD: 28.0 +/- 4.5 years). The rate-corrected QT interval (QTc) was calculated using Bazett's formula, and QT and QTc dispersions were defined as the maximum minus minimum values for the QT and QTc, respectively, from the 12-lead ECG. Spectral analysis of the heart rate variability generated values for the low- and high-frequency powers (LF and HF) and their ratio (LF/HF). Compared with values obtained in the supine position, tilting significantly increased QT (P < 0.05) and QTc dispersion (P < 0.01), the LF/HF ratio (P < 0.0001), and plasma norepinephrine concentration (P < 0.0001), and significantly decreased HF (P < 0.0001). QTc dispersion was positively correlated with the LF/HF ratio and plasma norepinephrine concentration, and negatively correlated with HF. These results suggest that head-up tilt testing increases QT dispersion by increasing sympathetic tone and/or decreasing vagal tone in healthy subjects.
authors.affiliation: Department of Laboratory Medicine, Oita Medical University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nakagawa
authors.forename: N
authors.initials: N
authors.lastname: Takahashi
authors.forename: T
authors.initials: T
authors.lastname: Iwao
authors.forename: H
authors.initials: H
authors.lastname: Yonemochi
authors.forename: T
authors.initials: T
authors.lastname: Ooie
authors.forename: M
authors.initials: M
authors.lastname: Hara
authors.forename: T
authors.initials: T
authors.lastname: Saikawa
authors.forename: M
authors.initials: M
authors.lastname: Ito
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D004562:Electrocardiography; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D009638:Norepinephrine / Q000097:blood; D012016:Reference Values; D016683:Supine Position / Q000502:physiology; D018667:Tilt-Table Test
chemical_list: D009638:Norepinephrine