title: Measure of the QT-RR dynamic coupling in patients with the long QT syndrome.
abstract: BACKGROUND
  The patients with the long QT syndrome type-1 (LQT-1) have an impaired adaptation of the QT interval to heart rate changes. Yet, the description of the dynamic QT-RR coupling in genotyped LQT-1 has never been thoroughly investigated.
  
  
  METHODS
  We propose a method to model the dynamic QT-RR coupling by defining a transfer function characterizing the relationship between a QT interval and its previous RR intervals measured from ambulatory Holter recordings. Three parameters are used to characterize the QT-RR coupling: a fast gain (Gain(F) ), a slow gain (Gain(L) ), and a time constant (τ). We investigated the values of these parameters across genders, and in genotyped LQT-1 patients with normal QTc interval duration (QTc < 470 ms).
  
  
  RESULTS
  The QT-RR dynamic profiles are significantly different between LQT-1 patients (97) and controls (154): LQT-1 have longer QTc interval (453 ± 35 vs. 384 ± 26 ms, P < 0.0001), and an increased dependency of the QT interval to previous RR changes revealed by a larger Gain(L) (0.22 ± 0.06 vs. 0.18 ± 0.07, P < 0.0001) and Gain(F) (0.05 ± 0.02 vs. 0.03 ± 0.01, P < 0.0001). Importantly, LQT-1 patients have a faster QT dynamic response to previous RR changes described by τ: 122 ± 44 vs. 172 ± 92 beats (P < 0.0001). This faster QT dynamic response of the QT-RR dynamic coupling remained in LQT-1 patients with QTc in a normal range (<430 ms).
  
  
  CONCLUSIONS
  The measurement of QT-RR dynamic coupling could be used in patients suspected to carry a concealed form of the LQT-1 syndrome, or to provide insights into the types of arrhythmogenic triggers a patient may be prone to.
authors.affiliation: Institute of Scientific Instruments, AS CR, Brno, Czech Republic. josef@isibrno.cz
authors.forename: Josef
authors.initials: J
authors.lastname: Halamek
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Couderc
authors.forename: Pavel
authors.initials: P
authors.lastname: Jurak
authors.forename: Vlastimil
authors.initials: V
authors.lastname: Vondra
authors.forename: Wojciech
authors.initials: W
authors.lastname: Zareba
authors.forename: Ivo
authors.initials: I
authors.lastname: Viscor
authors.forename: Pavel
authors.initials: P
authors.lastname: Leinveber
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D002940:Circadian Rhythm; D015331:Cohort Studies; D015716:Electrocardiography, Ambulatory / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006339:Heart Rate; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D008297:Male; D012016:Reference Values; D055815:Young Adult