title: Changes in QRS duration are associated with maximal exercise capacity in adult patients with repaired tetralogy of Fallot.
abstract: OBJECTIVE
  In adult patients with repaired tetralogy of Fallot (TF) QRS duration at rest seems to be a predictor of maximal exercise. We examined the relationship between QRS duration during exercise and exercise performance.
  
  
  METHODS
  In 57 consecutive TF patients QRS duration in V1 (ms) was measured at rest, at maximal exercise (Wmax, W), and at peak oxygen consumption (peak VO2, ml/min). Stroke volume (SV) was calculated from cardiac output, obtained by CO2 rebreathing. Spearman rank correlation was used to describe the relationship between QRS duration and exercise performance. Statistical significance was defined as P<0.05.
  
  
  RESULTS
  Seven patients, who didn't pass the anaerobic threshold, and one outlier (Wmax=340 W) were excluded, resulting in a sample of 49 patients (75.5% male; median age=24 years, range 16-43 years). QRS duration at rest (median=160 ms, range 78-194 ms) and at maximal exercise (median=153 ms, range 80-193 ms) did not differ significantly. The median change of QRS duration during exercise was -5 ms (range -31 to +83 ms). This was negatively correlated with Peak VO2 (2081+/-577 ml/min; rho=-0.33, P=0.02) and Wmax (182+/-53 Watt; rho=-0.33, P=0.02). In patients with QRS shortening peak VO2 and the exercise induced increase in SV were significantly higher than in patients with QRS shortening.
  
  
  CONCLUSIONS
  This study indicates that QRS shortening during exercise in TF patients is related with a better exercise performance. Lower increase in stroke volumes may be responsible for this difference. Further research is needed to elaborate these findings.
authors.affiliation: Internal Medicine, Department of Cardiology, University Hospital Gasthuisberg, Leuven, Belgium. Werner.Budts@uz.kuleuven.ac.be
authors.forename: W
authors.initials: W
authors.lastname: Budts
authors.forename: Johan
authors.initials: J
authors.lastname: Defoor
authors.forename: An
authors.initials: A
authors.lastname: Stevens
authors.forename: M
authors.initials: M
authors.lastname: Vanden Wyngaerd
authors.forename: Ph
authors.initials: P
authors.lastname: Moons
authors.forename: L
authors.initials: L
authors.lastname: Vanhees
mesh_terms: D000293:Adolescent; D000328:Adult; D006348:Cardiac Surgical Procedures; D004452:Echocardiography; D004562:Electrocardiography; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D012146:Rest; D012720:Severity of Illness Index; D013318:Stroke Volume; D013771:Tetralogy of Fallot / Q000503:physiopathology* / Q000601:surgery*; D013997:Time Factors; D016896:Treatment Outcome; D018497:Ventricular Dysfunction, Right / Q000503:physiopathology / Q000601:surgery