Author + information
- Received December 20, 1995
- Revision received June 12, 1996
- Accepted June 26, 1996
- Published online November 1, 1996.
- Hidekazu Hirao, MD,
- Wataru Shimizu, MD**,1,
- Takashi Kurita, MD,
- Kazuhiro Suyama, MD,
- Naohiko Aihara, MD,
- Shiro Kamakura, MD and
- Katsuro Shimomura, MD
- ↵**Present address and address for correspondence: Dr. Wataru Shimizu, Masonic Medical Research Laboratory, 2150 Bleecker Street, Utica, New York 13501-1787.
Objectives. This study was performed to evaluate the frequency dependency of ventricular repolarization and the effect of epinephrine in patients with congenital long QT syndrome (LQTS).
Background. The efficacy of pacemakers in addition to antiadrenergic therapy in the treatment of congenital LQTS has been reported.
Methods. Monophasic action potentials were recorded from right and left ventricular endocardium during atrial pacing at heart rates from 70 to 140 beats/min at baseline and from 100 to 140 beats/min during epinephrine infusion (0.1 μg/kg body weight per min) in 11 patients with congenital LQTS and 10 control patients. The response of monophasic action potential duration at 90% repolarization (MAPD90) and the dispersion of MAPD90 were examined.
Results. At baseline, both the MAPD90 and the dispersion of MAPD90 were significantly (p < 0.001) longer in the congenital LQTS group than the control group. The differences in these variables between the two groups significantly decreased (MAPD90: from 105 to 31 ms; dispersion of MAPD90: from 55 to 13 ms, p < 0.001) as heart rate was increased. Epinephrine prolonged the MAPD90 and increased the dispersion of MAPD90 significantly (p < 0.001) at all paced heart rates in the congenital LQTS group without frequency dependency but did not change in the control group. Thus, epinephrine increased the differences in these variables between the two groups.
Conclusions. The repolarization abnormalities in congenital LQTS were attenuated by increasing the heart rate, which supported the efficacy of pacemaker therapy. However, during sympathetic stimulation, the effects of increased heart rate on these repolarization abnormalities were limited.
↵1 Dr. Shimizu was supported in part by a grant from the Japan Cardiovascular Research Foundation, Osaka and by a Bayer Cardiovascular Disease Research Scholarship, Osaka, Japan.
This study was presented in part at the 44th Annual Scientific Session of the American College of Cardiology, New Orleans, Louisiana, March 1995.
- Received December 20, 1995.
- Revision received June 12, 1996.
- Accepted June 26, 1996.
- American College of Cardiology