title: Beat-to-beat T-wave amplitude variability in the long QT syndrome.
abstract: OBJECTIVE
  Long QT syndrome (LQTS) is a primary electrical disease characterized by QT prolongation and increased repolarization dispersion leading to T-wave amplitude beat-to-beat changes. We aimed to quantify beat-to-beat T-wave amplitude variability from ambulatory Holter recordings in genotyped LQTS patients.
  
  
  RESULTS
  Seventy genotyped LQTS patients (mean age 23 +/- 15 years, 42 males, 50% LQT1, 39% LQT2, and 11% LQT3) and 70 normal matched control subjects underwent a 24-h digital Holter recording. Using the Tvar software (Ela Medical, Sorin group), the beat-to-beat variance of the T-wave amplitude (TAV in microV) [corrected] was assessed on 50-ms consecutive clusters during three 1-h periods: one with around average diurnal heart rate (Day Fast), one nocturnal period (Night), and one diurnal period with around average nocturnal heart rate (Day Slow). TAV was increased in LQTS patients during the two diurnal periods but not at night (during the Day Fast period, mean TAV was 34 +/- 20 microV [corrected] in LQTS patients vs. 27 +/- 10 microV [corrected] in controls, P < 0.05). This effect depended on the genotype. In LQT1, TAV was larger when compared with controls for both Day Fast and Slow periods, but in LQT2 only Day Fast shows higher TAV. Oppositely, in LQT3 the TAV was higher than in the control group during the Day slow period (mean TAV = 34 +/- 20 vs. 25 +/- 8 microV [corrected] in controls, P < 0.05).
  
  
  CONCLUSIONS
  In genotyped LQTS patients beat-to-beat T-wave amplitude variability was increased when compared with control subjects. That pattern was modulated by circadian influences in a gene-dependent manner.
authors.affiliation: Cardiology Department, Lariboisière Hospital APHP, University Paris Diderot, Paré, France. fabrice.extramiana@lrb.aphp.fr
authors.forename: Fabrice
authors.initials: F
authors.lastname: Extramiana
authors.forename: Charif
authors.initials: C
authors.lastname: Tatar
authors.forename: Pierre
authors.initials: P
authors.lastname: Maison-Blanche
authors.forename: Isabelle
authors.initials: I
authors.lastname: Denjoy
authors.forename: Anne
authors.initials: A
authors.lastname: Messali
authors.forename: Patrick
authors.initials: P
authors.lastname: Dejode
authors.forename: Frank
authors.initials: F
authors.lastname: Iserin
authors.forename: Antoine
authors.initials: A
authors.lastname: Leenhardt
mesh_terms: D000367:Age Factors; D002940:Circadian Rhythm; D004562:Electrocardiography; D015716:Electrocardiography, Ambulatory; D005260:Female; D006339:Heart Rate; D006801:Humans; D008133:Long QT Syndrome / Q000151:congenital / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology*; D008297:Male