β-blockers protect against dispersion of repolarization during exercise in congenital long-QT syndrome type 1

J Cardiovasc Electrophysiol. 2011 Oct;22(10):1141-6. doi: 10.1111/j.1540-8167.2011.02091.x. Epub 2011 Jun 2.

Abstract

Introduction: 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.

Methods and 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).

Conclusion: 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.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adrenergic beta-Antagonists / therapeutic use*
  • Adult
  • Death, Sudden, Cardiac / etiology
  • Death, Sudden, Cardiac / prevention & control
  • Double-Blind Method
  • Electrocardiography
  • Exercise*
  • Female
  • Heart Conduction System / drug effects*
  • Heart Conduction System / physiopathology
  • Heart Rate / drug effects
  • Humans
  • Male
  • Middle Aged
  • Ohio
  • Propranolol / therapeutic use*
  • Romano-Ward Syndrome / complications
  • Romano-Ward Syndrome / drug therapy*
  • Romano-Ward Syndrome / physiopathology
  • Syncope / etiology
  • Syncope / physiopathology
  • Syncope / prevention & control
  • Time Factors
  • Treatment Outcome
  • Young Adult

Substances

  • Adrenergic beta-Antagonists
  • Propranolol