Japanese Journal of Electrocardiology
Online ISSN : 1884-2437
Print ISSN : 0285-1660
ISSN-L : 0285-1660
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Volume 35, Issue 3
Displaying 1-11 of 11 articles from this issue
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  • Proarrhythmic Properties of the Atrioventricular Block Heart of the Rabbit
    Mihoko Hagiwara, Naoto Kondo, Toshiki Chiba, Akira Takahara
    2015 Volume 35 Issue 3 Pages 169-176
    Published: 2015
    Released on J-STAGE: March 11, 2016
    DOIhttps://doi.org/10.5105/jse.35.169
    JOURNAL FREE ACCESS
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    The proarrhythmic potential of the rabbit heart was investigated under the condition of acute or chronic bradycardia caused by atrioventricular (AV) block. New Zealand White rabbits were anesthetized with isoflurane, and electrocardiogram and blood pressure were recorded. In the experiment using the acute bradycardia model, the ventricle was electrically driven at 60 beats/min after the AV node ablation. Intravenous administration of nifekalant (0.03, 0.3 and 3 mg/kg) prolonged the QT interval in a dose-dependent manner (n=6), and torsade de pointes (TdP) was spontaneously induced in 5 animals. In another series of experiment using the chronic bradycardia model, escape junctional or idioventricular rhythm stably appeared after the AV node ablation in 14 out of 23 animals, and onset of TdP was recorded by Holter monitoring. These results suggest that acute bradycardia can unmask proarrhythmic potential of the rabbit heart in the presence of a QT interval-prolonging drug.
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  • Assessing the Normal Value of STV-QT
    Takao Ohmuta, Masashi Kasao, Akira Nakazawa, Takako Ono, Kazuyuki Mits ...
    2015 Volume 35 Issue 3 Pages 177-182
    Published: 2015
    Released on J-STAGE: March 11, 2016
    DOIhttps://doi.org/10.5105/jse.35.177
    JOURNAL FREE ACCESS
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    The measurement of short-term variability of QT interval (STV-QT) is well known for the quantitative evaluation of the instability of the repolarization phase of the heart ventricles and has been, established by clinical and experimental studies. The STV-QT value is suspected to be clinically useful, since the measurement method is non-invasive, measurement time is short (around one minute), and measurement equipment is simple (only ECG recording is required). There have been many reports published concerning the usefulness of STV-QT measurement for discriminating between drug-induced QT prolongation and congenital long QT syndrome, for example, and for prediction of torsade de pointes. In this study, we measured the normal value of STV-QT according to age and sex. STV-QTs were measured in 205 healthy volunteers ranging in age from 20 to 65. The normal STV-QT value ranges 0.7 to 4.7 msec (mean value 2.7msec, standard deviation 1.0msec). No significant differences according to age or sex were observed.
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  • Spontaneous Electrical Activity of the Pulmonary Vein Myocardium
    Yayoi Tsuneoka, Shogo Hamaguchi, Iyuki Namekata, Hikaru Tanaka
    2015 Volume 35 Issue 3 Pages 183-191
    Published: 2015
    Released on J-STAGE: March 11, 2016
    DOIhttps://doi.org/10.5105/jse.35.183
    JOURNAL FREE ACCESS
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    The pulmonary vein myocardium is receiving attention as the source of ectopic electrical activity underlying atrial fibrillation. Electrophysiological and pharmacological analysis in isolated pulmonary vein myocardia from various experimental animal species have revealed that pulmonary vein cardiomyocytes have an intrinsic ability to generate spontaneous action potentials. The spontaneous electrical activity of the pulmonary vein myocardium is accompanied by elevation and oscillation of intracellular Ca2+ concentration, and the activity of the sarcolemmal Na+-Ca2+ exchanger to extrude intracellular Ca2+ in exchange for three extracellular Na+ contributes to the diastolic depolarization triggering the action potential. The lower inwardly rectifying repolarizing K+ current density in the pulmonary vein cardiomyocyte plays a permissive role. Variation in the pattern, waveform and frequency of firing is observed among animal species, which appears to be the result of differences in the type and density of K+ currents involved in early and late repolarization. Pulmonary vein automaticity is also affected by various neurohumoral substances and pharmacological agents, and by pathological status such as the degree of tissue stretch. Studies on the mechanisms and regulation of pulmonary vein automaticity could lead to the development of novel therapeutic strategies for atrial fibrillation.
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