Response of beat-by-beat QT variability to sympathetic stimulation in the LQT1 form of congenital long QT syndrome.
OBJECTIVE
The purpose of this study was to test the hypothesis that the lability of beat-by-beat QT variability is prominent during sympathetic stimulation in LQT1 patients. We analyzed beat-by-beat QT variability using a newly developed program and applied cross-correlation methods in LQT1 patients before and after epinephrine infusion.


BACKGROUND
Studies suggest that cardiac events associated with sympathetic stimulation are more common in the LQT1 form than the LQT2 and LQT3 forms of congenital long QT syndrome (LQTS). Although beat-by-beat alternation of T-wave morphology is observed in LQTS, its objective estimation is difficult because of complicated T-wave morphology.


METHODS
Twelve-lead ECG was recorded under baseline conditions and during epinephrine infusion (0.1 mug/kg/min) in 14 LQT1 and five control patients. We measured beat-by-beat QT interval by a cross-correlation technique. Mean of successive changes in RR (DeltaRR), QT (DeltaQT), standard deviation of DeltaRR (SD-DeltaRR), DeltaQT (SD-DeltaQT), and QTI (QT/ RR) before and after epinephrine were compared between the two groups.


RESULTS
No significant differences in any parameters were observed between the two groups under baseline conditions. DeltaQT, SD-DeltaQT, and QTI were increased in LQT1 but not in control patients during epinephrine (LQT1: DeltaQT 2.3-4.2 ms, SD-DeltaQT 2.2-4.1, QTI 0.10-0.22, P < .005 vs baseline;


METHODS
DeltaQT 2.5-2.4 ms, SD-DeltaQT 1.9-2.1, QTI 0.08-0.09: P = NS vs baseline).


CONCLUSIONS
Beat-by-beat QT variability analyzed by the cross-correlation method was greater in LQT1 patients during epinephrine infusion, suggesting sympathetic stimulation accentuates beat-by-beat alternation of repolarization in LQT1 patients.
Satomi
Kazuhiro
K
Division of Cardiology, Department of Internal MedicineNational Cardiovascular Center, Suita, Japan.
Shimizu
Wataru
W
Takaki
Hiroshi
H
Suyama
Kazuhiro
K
Kurita
Takashi
T
Aihara
Naohiko
N
Kamakura
Shiro
S
D000328:Adult; D004562:Electrocardiography; D004837:Epinephrine; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008133:Long QT Syndrome / Q000151:congenital* / Q000503:physiopathology*; D013566:Sympathomimetics
D013566:Sympathomimetics; D004837:Epinephrine