title: β-blockers protect against dispersion of repolarization during exercise in congenital long-QT syndrome type 1.
abstract: BACKGROUND
  β-Blocker therapy reduces syncope and sudden death in long-QT syndrome type 1 (LQT1), but the mechanism of protection is incompletely understood. This study tested the hypothesis that β-blockade reduces QT prolongation and dispersion of repolarization, measured as the T peak-to-end interval (T(pe) ), during exercise and recovery in LQT1 patients.
  
  
  RESULTS
  QT and T(pe) were measured in 10 LQT1 patients (33 ± 13 years) and 35 normal subjects (32 ± 12 years) during exercise tests on and off β-blockade. In LQT1 patients, β-blockade reduced QT (391 ± 25 milliseconds vs 375 ± 26 milliseconds, P = 0.04 during exercise; 419 ± 41 milliseconds vs 391 ± 39 milliseconds, P = 0.02 during recovery) and markedly reduced T(pe) (91 ± 26 milliseconds vs 67 ± 19 milliseconds, P = 0.03 during exercise; 103 ± 26 milliseconds vs 78 ± 11 milliseconds, P = 0.02 during recovery). In contrast, in normal subjects, β-blockade had no effect on QT (320 ± 17 milliseconds vs 317 ± 16 milliseconds, P = 0.29 during exercise; 317 ± 13 milliseconds vs 315 ± 14 milliseconds, P = 0.15 during recovery) and mildly reduced T(pe) (69 ± 13 milliseconds vs 61 ± 11 milliseconds, P = 0.01 during exercise; 77 ± 19 milliseconds vs. 68 ± 14 milliseconds, P < 0.001 during recovery).
  
  
  CONCLUSIONS
  In LQT1 patients, β-blockers reduced QT and T(pe) during exercise and recovery, supporting the theory that β-blocker therapy protects LQT1 patients by reducing dispersion of repolarization during exercise and recovery.
authors.affiliation: Heart and Vascular Research Center, MetroHealth Campus of Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Lee W
authors.initials: LW
authors.lastname: Gemma
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Ward
authors.forename: Mary M
authors.initials: MM
authors.lastname: Dettmer
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Ball
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Leo
authors.forename: Danielle N
authors.initials: DN
authors.lastname: Doria
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Kaufman
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use*; D000328:Adult; D016757:Death, Sudden, Cardiac / Q000209:etiology / Q000517:prevention & control; D004311:Double-Blind Method; D004562:Electrocardiography; D015444:Exercise; D005260:Female; D006329:Heart Conduction System / Q000187:drug effects* / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D009820:Ohio; D011433:Propranolol / Q000627:therapeutic use*; D029597:Romano-Ward Syndrome / Q000150:complications / Q000188:drug therapy* / Q000503:physiopathology; D013575:Syncope / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000319:Adrenergic beta-Antagonists; D011433:Propranolol