title: Pronounced Shortening of QT Interval With Mexiletine Infusion Test in Patients With Type 3 Congenital Long QT Syndrome.
abstract: BACKGROUND
  Mexiletine is often used for medical therapy in LQT3 patients, however, the usefulness of mexiletine infusion test for LQT3 patients has not been reported. The aim of this study was to evaluate the usefulness of mexiletine infusion test for detecting LQT3 patients.
  
  
  RESULTS
  We analyzed response in 12-lead electrocardiogram parameters measured in II or V5 to i.v. mexiletine infusion (2 mg/kg) during sinus rhythm among 31 genotype-positive LQT patients (29 ± 18 years, 12 male). Change in QTc interval after mexiletine was compared between LQT3 (n=15, 24 ± 21 years, 9 male) and other LQT patients (4 LQT1 and 12 LQT2; 34 ± 14 years, 3 male). Baseline RR, QT, and QTc interval were not different between the 2 groups (981 ± 182 vs. 1,023 ± 192 ms; 550 ± 94 vs. 524 ± 75 ms; 556 ± 66 vs. 520 ± 62 ms, respectively). While QTc interval was shortened with mexiletine in both groups (P<0.0001 vs. baseline), degree of QTc shortening (∆QTc) was significantly larger in LQT3 than in LQT1/LQT2 patients (99 ± 39 vs. 48 ± 32 ms; P=0.0004). The sensitivity, specificity and predictive accuracy of mexiletine infusion test for differentiating LQT3 from LQT1/LQT2 were 86.7%, 81.3% and 81.3%, respectively, and the optimal cut-off for ∆QTc was 69 ms on receiver operating characteristic analysis. No pro-arrhythmic event was observed.
  
  
  CONCLUSIONS
  Pronounced shortening of QT interval with mexiletine may facilitate genetic testing in patients with LQT3 syndrome.
authors.affiliation: Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center.
authors.forename: Moritoshi
authors.initials: M
authors.lastname: Funasako
authors.forename: Takeshi
authors.initials: T
authors.lastname: Aiba
authors.forename: Kohei
authors.initials: K
authors.lastname: Ishibashi
authors.forename: Ikutaro
authors.initials: I
authors.lastname: Nakajima
authors.forename: Koji
authors.initials: K
authors.lastname: Miyamoto
authors.forename: Yuko
authors.initials: Y
authors.lastname: Inoue
authors.forename: Hideo
authors.initials: H
authors.lastname: Okamura
authors.forename: Takashi
authors.initials: T
authors.lastname: Noda
authors.forename: Shiro
authors.initials: S
authors.lastname: Kamakura
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Anzai
authors.forename: Teruo
authors.initials: T
authors.lastname: Noguchi
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yasuda
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Kengo
authors.initials: K
authors.lastname: Fukushima Kusano
authors.forename: Hisao
authors.initials: H
authors.lastname: Ogawa
authors.forename: Wataru
authors.initials: W
authors.lastname: Shimizu
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology*; D008297:Male; D008801:Mexiletine / Q000008:administration & dosage*; D008875:Middle Aged
chemical_list: D008801:Mexiletine