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33rd International Congress on Electrocardiology

International Society of Electrocardiology

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Difference Between Acute and Chronic Effects of Amiodarone on QT Versus RR Relationship

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  • corresponding author presenting/speaker J. Iwamoto - University of Toyama, Toyama, Japan
  • A. Hujiki - University of Toyama, Toyama, Japan
  • T. Sakamoto - University of Toyama, Toyama, Japan
  • H. Nagasawa - University of Toyama, Toyama, Japan
  • K. Mizumaki - University of Toyama, Toyama, Japan
  • H. Inoue - University of Toyama, Toyama, Japan

33rd International Congress on Electrocardiology. Cologne, 28.06.-01.07.2006. Düsseldorf, Köln: German Medical Science; 2007. Doc06ice052

The electronic version of this article is the complete one and can be found online at: http://www.egms.de/en/meetings/ice2006/06ice052.shtml

Published: February 8, 2007

© 2007 Iwamoto et al.
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Outline

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The aim of this study was to determine short- and long-term effects of amiodarone on QT versus RR relationship obtained from 24-hour Holter ECG recordings.

Methods: We studied 24 patients with amiodarone therapy (average 181 mg/day); 12 patients with long-term (>one month) and 12 patients with short-term administration (2 weeks-one month). There was no difference in daily dosage of amiodarone; 186±32mg/day in short-term treatment group and 177±44 mg/day in long-term treatment group. QT interval and heart rate were determined automatically from 24-hour Holter ECG digital data. QT interval was measured from signal averaged ECG wave obtained by averaging consecutive beats during each 15 second period over 24 hours. To characterize dynamic changes in QT interval in patients with amiodarone therapy, QT interval nomogram from 422 healthy subjects served as the reference. QT deviation was defined as difference between QT intervals of patients and normal values.

Results: QT deviation at a heart rate of 50 beats/min was 57±26 msec in short-term group and 80±37 msec in long-term group (P=0.055). However, QT deviation at heart rates over 60 beats/min was definitely greater in long-term group than in short-term group. For example, QT deviation at a heart rate of 60 beats/min was 51±34 msec in short-term group and 82±34 msec in long-term group (P=0.015) and that at a heart rate of 90 beats/min was 38±29 msec in short-term group and 70±37 msec in long-term group (P=0.029).

Conclusions: As compared with acute effect, chronic effect of amiodarone on ventricular repolarization was definitely greater at higher heart rates than at lower heart rates. This finding could be related to difference between short-term and long-term pharmacological effects of amiodarone.