title: Dynamics of QT interval in a patient with long QT syndrome and a normal QT interval.
abstract: A case report of a 15-year-old girl who experienced syncope and torsades de pointes is presented. The girl had a normal QT interval (QTc=0.37 sec) on the resting electrocardiogram (ECG). Infusion of isoproterenol induced QT prolongation (QTc=0.62 sec) and frequent occurrence of multiform ventricular premature beats. Her Holter ECG showed a prolongation of the QTc interval with a shortening of the RR interval. Low-frequency power (LF) and high-frequency power (HF) of heart rate variability were evaluated from the Holter ECG. The patient showed a statistically significant negative QTc/HF and a significant positive QTc/(LF/HF) relationship, whereas none of the age- and sex-matched healthy subjects showed these relationships. The slope of the QT/RR relationship for the patient was below the lower limit of the normal range. This report describes the unusual relationship of QT interval to RR interval and heart rate variability in a long QT syndrome patient with a normal QT interval on resting ECG.
authors.affiliation: Department of Laboratory Medicine, Oita Medical University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nakagawa
authors.forename: T
authors.initials: T
authors.lastname: Iwao
authors.forename: S
authors.initials: S
authors.lastname: Ishida
authors.forename: N
authors.initials: N
authors.lastname: Takahashi
authors.forename: H
authors.initials: H
authors.lastname: Yonemochi
authors.forename: M
authors.initials: M
authors.lastname: Asada
authors.forename: S
authors.initials: S
authors.lastname: Shimada
authors.forename: T
authors.initials: T
authors.lastname: Saikawa
authors.forename: M
authors.initials: M
authors.lastname: Ito
mesh_terms: D000293:Adolescent; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology*; D013575:Syncope / Q000503:physiopathology*; D016171:Torsades de Pointes / Q000503:physiopathology