Key result
In a 15-year-old girl with long QT syndrome and normal resting ECG, isoproterenol induced QT prolongation, and Holter ECG revealed abnormal QTc/HF and QTc/(LF/HF) relationships.
Case Report (n=1)
Highlights the unusual dynamics of QT interval and heart rate variability in a patient with long QT syndrome but a normal resting QT interval, which was unmasked by isoproterenol and Holter monitoring.
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Isoproterenol testing and Holter QTc-HRV analysis may aid LQTS diagnosis when resting ECG is normal; leaves open generalizability and clinical utility.
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.
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Nakagawa et al. (1998) conducted a case report in Long QT syndrome (n=1). Isoproterenol infusion and Holter ECG monitoring vs. Age- and sex-matched healthy subjects was evaluated on QT interval dynamics and heart rate variability relationships. In a 15-year-old girl with long QT syndrome and normal resting ECG, isoproterenol induced QT prolongation, and Holter ECG revealed abnormal QTc/HF and QTc/(LF/HF) relationships.
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