title: Assessing real-time RR-QT frequency-domain measures of coupling and causality through inhomogeneous point-process bivariate models.
abstract: Ventricular repolarization instability is known to be related to arrhythmogenesis and increased risk of sudden cardiac death. These repolarization dynamics are linked to the distance between T-wave and Q-wave occurrences (QT) on the ECG, and they are coupled with R-wave to R-wave interval variability (RRV). Several efforts have been dedicated to the analysis of QT-RR interactions in order to provide both a quantification of the coupling and estimates of intrinsic repolarization dynamics. However, a methodology able to quantify dynamic changes in repolarization variability unrelated to RRV dynamics is still needed. In this study, we propose a bivariate model embedded within a multiple inhomogeneous point-process framework to obtain time-varying tracking of (causal) interactions between QT variability (QTV), a marker of repolarization variability, and RRV. Data from 15 healthy subjects undergoing a tilt table test were analyzed. Our results demonstrate that the model effectively captures the time-varying mutual QTV-RRV interactions. The analysis of time-varying coherence confirms that head-up tilt is associated with a decrease in linear QTV-RRV coupling, while time-varying directed coherence shows that intrinsic QTV becomes more prominent during head-up tilt.
authors.forename: G
authors.initials: G
authors.lastname: Valenza
authors.forename: M
authors.initials: M
authors.lastname: Orini
authors.forename: L
authors.initials: L
authors.lastname: Citi
authors.forename: A
authors.initials: A
authors.lastname: Minchole
authors.forename: E
authors.initials: E
authors.lastname: Pueyo
authors.forename: P
authors.initials: P
authors.lastname: Laguna
authors.forename: R
authors.initials: R
authors.lastname: Barbieri
mesh_terms: D000328:Adult; D000465:Algorithms; D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D003198:Computer Simulation; D004562:Electrocardiography / Q000379:methods*; D004867:Equipment Design; D005260:Female; D064368:Healthy Volunteers; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D010363:Pattern Recognition, Automated; D011336:Probability; D012815:Signal Processing, Computer-Assisted; D018667:Tilt-Table Test