title: Exercise induces biventricular mechanical dyssynchrony in children with repaired tetralogy of Fallot.
abstract: OBJECTIVE
  The mechanisms underlying adverse electro-mechanical interaction after tetralogy of Fallot (TOF) repair remain unclear. This study investigated biventricular dyssynchrony in children with TOF and its relationship to exercise, QRS duration (QRSd) and ventricular mechanics.
  
  
  METHODS
  29 asymptomatic children (5-18 years) with repaired TOF were prospectively evaluated by MRI, cardiopulmonary exercise testing and echocardiography at rest and during bicycle exertion. Their dyssynchrony results were compared with those of 44 resting and 27 exercising, age- and sex-matched controls. An intraventricular dyssynchrony index was calculated from the SD of regional time intervals in 12 left ventricular (LV) 'Ts LV-12SD' and eight right ventricular (RV) 'Ts RV-8SD' segments. Ventricular size, volumes, ejection fractions, pulmonary regurgitant volumes and peak oxygen consumption and N-terminal BNP levels were quantified in the patients.
  
  
  RESULTS
  Despite moderate RV dilatation (median indexed RV end-diastolic volume 145.2 ml/m(2)) and right bundle branch block (median QRSd 130 ms) compared with controls, children with TOF demonstrated neither RV nor LV dyssynchrony at rest (Ts RV-8SD, 37.9±10.2 vs 44.3±10.3, 95% CI -11.8 to -0.99, p=0.02; Ts LV-12SD, 38.6±16.8 vs 34.0±10.8, 95% CI -1.8 to 11.0, p=0.16). Exercise stress induced biventricular dyssynchrony in patients with TOF but not in controls (Ts RV-8SD, 59.9±34.4 vs 28.2±10.4, p<0.0001, 95% CI 17.2 to 46.3; Ts LV-12SD, 48.0±18.6 vs 31.9±10.7, 95% CI 7.9 to 24.4, p=0.002). This was unrelated to QRSd, ventricular volumes and function, or peak oxygen consumption.
  
  
  CONCLUSIONS
  Exercise induces biventricular mechanical dyssynchrony in children with TOF.
authors.affiliation: The Labatt Family Heart Center, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: S Lucy
authors.initials: SL
authors.lastname: Roche
authors.forename: Lars
authors.initials: L
authors.lastname: Grosse-Wortmann
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Redington
authors.forename: Cameron
authors.initials: C
authors.lastname: Slorach
authors.forename: Gareth
authors.initials: G
authors.lastname: Smith
authors.forename: Paul F
authors.initials: PF
authors.lastname: Kantor
authors.forename: Mark K
authors.initials: MK
authors.lastname: Friedberg
mesh_terms: D000293:Adolescent; D001145:Arrhythmias, Cardiac / Q000209:etiology*; D002648:Child; D002675:Child, Preschool; D004452:Echocardiography; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography; D008297:Male; D011446:Prospective Studies; D011665:Pulmonary Valve Insufficiency / Q000209:etiology; D013771:Tetralogy of Fallot / Q000150:complications* / Q000601:surgery; D018487:Ventricular Dysfunction, Left / Q000209:etiology*; D018497:Ventricular Dysfunction, Right / Q000209:etiology*