title: Instability of repolarization in LQTS mutation carriers compared to healthy control subjects assessed by vectorcardiography.
abstract: BACKGROUND
  Potassium channel dysfunction in congenital and acquired forms of long QT syndrome types 1 and 2 (LQT1 and LQT2) increases the beat-to-beat variability of the QT interval.
  
  
  OBJECTIVE
  To study about the little known variability (instability) of other aspects of ventricular repolarization (VR) in humans by using vectorcardiography.
  
  
  METHODS
  Beat-to-beat analysis was performed regarding vectorcardiography derived RR, QRS, and QT intervals, as well as T vector- and T vector loop-based parameters during 1-minute recordings of uninterrupted sinus rhythm at rest in 41 adult LQT1 (n = 31) and LQT2 (n = 10) mutation carriers and 41 age- and sex-matched control subjects. The short-term variability for each parameter, describing the mean orthogonal distance to the line of identity on the Poincaré plot, was calculated.
  
  
  RESULTS
  Mutation carriers showed significantly larger (by a factor 2) instability in most VR parameters compared to controls despite higher instantaneous heart rate variability (STVRR) in the control group. The longer the QT interval, the greater was its instability, and the instability of VR dispersion measures.
  
  
  CONCLUSIONS
  A greater instability of most aspects of VR already at rest seems to be a salient feature in both LQT1 and LQT2, which might pave the way for early afterdepolarizations and torsades de pointes ventricular tachycardia. In contrast, no signs of increased VR dispersion per se were observed in mutation carriers.
authors: Department of Molecular and Clinical Medicine/Cardiology, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. farzad.vahedi@vgregion.se
authors: Farzad
authors: F
authors: Vahedi
authors: Ulla-Britt
authors: UB
authors: Diamant
authors: Gunilla
authors: G
authors: Lundahl
authors: Gabriel
authors: G
authors: Bergqvist
authors: Lennart
authors: L
authors: Gransberg
authors: Steen M
authors: SM
authors: Jensen
authors: Lennart
authors: L
authors: Bergfeldt
mesh_terms: D000328:Adult; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009154:Mutation; D014672:Vectorcardiography / Q000379:methods*
keywords: ACA; AP; Aborted cardiac arrest; Action potential from ventricular myocyte; Amplitude of the maximum QRS vector in space; HR; Long QT syndrome; QRS(amplitude); Repolarization; Short-term variability; T peak to T end, the last part of the QT interval and final repolarization in the 3-dimensional QRST complex; Vectorcardiography; heart rate; the amplitude of the maximum T vector in space