title: Bradycardia-dependent ECG changes in Brugada syndrome.
abstract: BACKGROUND
  In patients with Brugada syndrome (BS), ventricular fibrillation (VF) occurs mainly during sleep; therefore, not only vagal activity but also bradycardia dependent changes in ECG may relate to the nighttime occurrence of VF. The present study aimed to examine the difference in bradycardia-dependent changes in the ECG of symptomatic and asymptomatic BS patients.
  
  
  RESULTS
  Twenty-one patients with BS were categorized into symptomatic (n = 9) and asymptomatic (n = 12) groups. During the electrophysiologic study, the ECG changes were evaluated at RR intervals of 400, 600, 750, 1,000 and 1,100 ms during extrastimulation from the right atrium. The ST levels in V2, and the QT interval in both V2 and V5 were measured. Along with an increase in the RR interval from 400 to 1,100 ms, the ST levels in V2 increased in both groups; the increase did not differ between the 2 groups. In both leads V2 and V5, the prolongation of the QT interval along with an increase in the RR interval from 400 to 1,100 ms was significantly smaller and the QT intervals at an RR interval of 1,100 ms were significantly shorter in the symptomatic than in the asymptomatic group.
  
  
  CONCLUSIONS
  In patients with BS, the ST elevation was augmented during bradycardia to a similar extent in both symptomatic and asymptomatic patients. However, a inhibited prolongation of the QT interval during bradycardia was characteristic of symptomatic patients. These unique repolarization dynamics could relate to the nighttime occurrence of VF during bradycardia in patients with BS.
authors.affiliation: The Second Department of Internal Medicine, Faculty of Medicine, University of Toyama, Toyama, Japan. kmizu@med.u-toyama.ac.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Mizumaki
authors.forename: Akira
authors.initials: A
authors.lastname: Fujiki
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Nishida
authors.forename: Masao
authors.initials: M
authors.lastname: Sakabe
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tsuneda
authors.forename: Masataka
authors.initials: M
authors.lastname: Sugao
authors.forename: Jotaro
authors.initials: J
authors.lastname: Iwamoto
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Nagasawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Inoue
mesh_terms: D000328:Adult; D000368:Aged; D001919:Bradycardia / Q000150:complications / Q000503:physiopathology*; D016022:Case-Control Studies; D004562:Electrocardiography; D006325:Heart Atria / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D013577:Syndrome; D014693:Ventricular Fibrillation / Q000150:complications / Q000503:physiopathology*