title: Wiener-Granger causality in QT-HP variability interactions.
abstract: The study exploits a Wiener-Granger causality (WGC) approach in the time domain to assess directionality of the dynamical interactions between QT interval and heart period (HP) during a graded head-up tilt protocol challenging the cardiovascular control as a function of the tilt table inclination. QT interval and HP are approximated from the surface ECG as the temporal distance between the R-wave apex and T-wave offset and between two consecutive R-wave peaks respectively. The adopted WGC approach accounts for the confounding effect of respiration (RESP) affecting both QT and HP. Causality ratios (CRs) from HP to QT given RESP (CRHP→QT|RESP) and from QT to HP given RESP (CRQT→HP|RESP) were computed and their significance was tested via F-test. We found that, regardless of the tilt table angle, CRHP→QT|RESP is significant, while CRQT→HP|RESP is negligible. CRHP→QT|RESP showed a trend towards a decrease with tilt table angle. These findings suggested that the causal direction from HP over QT is dominant compared to the reverse one and sympathetic activation induced a QT-HP uncoupling.
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
authors.forename: Vlasta
authors.initials: V
authors.lastname: Bari
authors.forename: Andrea
authors.initials: A
authors.lastname: Marchi
authors.forename: Beatrice
authors.initials: B
authors.lastname: De Maria
authors.forename: Sergio
authors.initials: S
authors.lastname: Cerutti
mesh_terms: D000328:Adult; D000465:Algorithms; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000502:physiology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D055815:Young Adult