Dynamics of QT interval in a patient with long QT syndrome and a normal QT interval.
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.
Nakagawa
M
M
Department of Laboratory Medicine, Oita Medical University, Japan.
Iwao
T
T
Ishida
S
S
Takahashi
N
N
Yonemochi
H
H
Asada
M
M
Shimada
S
S
Saikawa
T
T
Ito
M
M
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