title: Differential effects of beta-blockade on dispersion of repolarization in the absence and presence of sympathetic stimulation between the LQT1 and LQT2 forms of congenital long QT syndrome.
abstract: OBJECTIVE
  This study compared the effects of beta-blockade on transmural and spatial dispersion of repolarization (TDR and SDR, respectively) between the LQT1 and LQT2 forms of congenital long QT syndrome (LQTS).
  
  
  BACKGROUND
  The LQT1 form is more sensitive to sympathetic stimulation and more responsive to beta-blockers than either the LQT2 or LQT3 forms.
  
  
  METHODS
  Eighty-seven-lead, body-surface electrocardiograms (ECGs) were recorded before and after epinephrine infusion (0.1 microg/kg body weight per min) in the absence and presence of oral propranolol (0.5-2.0 mg/kg per day) in 11 LQT1 patients and 11 LQT2 patients. The Q-T(end) interval, the Q-T(peak) interval and the interval between T(peak) and T(end) (T(p-e)), representing TDR, were measured and averaged from 87-lead ECGs and corrected by Bazett's method (corrected Q-T(end) interval [cQT(e)], corrected Q-T(peak) interval [cQT(p)] and corrected interval between T(peak) and T(end) [cT(p-e)]). The dispersion of cQT(e) (cQT(e)-D) was obtained among 87 leads and was defined as the interval between the maximum and minimum values of cQT(e).
  
  
  RESULTS
  Propranolol in the absence of epinephrine significantly prolonged the mean cQT(p) value but not the mean cQT(e) value, thus decreasing the mean cT(p-e) value in both LQT1 and LQT2 patients; the differences with propranolol were significantly larger in LQT1 than in LQT2 (p < 0.05). The maximum cQT(e), minimum cQT(e) and cQT(e)-D were not changed with propranolol. Propranolol completely suppressed the influence of epinephrine in prolonging the mean cQT(e), maximum cQT(e) and minimum cQT(e) values, as well as increasing the mean cT(p-e) and cQT(e)-D values in both groups.
  
  
  CONCLUSIONS
  Beta-blockade under normal sympathetic tone produces a greater decrease in TDR in the LQT1 form than in the LQT2 form, explaining the superior effectiveness of beta-blockers in LQT1 versus LQT2. Beta-blockers also suppress the influence of sympathetic stimulation in increasing TDR and SDR equally in LQT1 and LQT2 syndrome.
authors.affiliation: Division of Cardiology, Department of Internal Medicine, National Cardiovascular Center, Suita, Osaka, Japan. wshimizu@hsp.ncvc.go.jp
authors.forename: Wataru
authors.initials: W
authors.lastname: Shimizu
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Tanabe
authors.forename: Takeshi
authors.initials: T
authors.lastname: Aiba
authors.forename: Masashi
authors.initials: M
authors.lastname: Inagaki
authors.forename: Takashi
authors.initials: T
authors.lastname: Kurita
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Suyama
authors.forename: Noritoshi
authors.initials: N
authors.lastname: Nagaya
authors.forename: Atsushi
authors.initials: A
authors.lastname: Taguchi
authors.forename: Naohiko
authors.initials: N
authors.lastname: Aihara
authors.forename: Kenji
authors.initials: K
authors.lastname: Sunagawa
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Nakamura
authors.forename: Tohru
authors.initials: T
authors.lastname: Ohe
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Towbin
authors.forename: Silvia G
authors.initials: SG
authors.lastname: Priori
authors.forename: Shiro
authors.initials: S
authors.lastname: Kamakura
mesh_terms: D000293:Adolescent; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D018780:Body Surface Potential Mapping; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006329:Heart Conduction System / Q000187:drug effects* / Q000503:physiopathology; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011433:Propranolol / Q000494:pharmacology*; D013564:Sympathetic Nervous System / Q000503:physiopathology
chemical_list: D000319:Adrenergic beta-Antagonists; D011433:Propranolol