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Cardiovascular Research 1997 34(3):453-463; doi:10.1016/S0008-6363(97)00067-9
© 1997 by European Society of Cardiology
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Copyright © 1997, European Society of Cardiology

Role of interventricular dispersion of repolarization in acquired torsade-de-pointes arrhythmias: reversal by magnesium

S.C. Verduyn, M.A. Vos*, J. van der Zande, F.F. van der Hulst and H.J. Wellens

Department of Cardiology, Cardiovascular Research Institute Maastricht, University of Limburg, Maastricht, P.O. Box 5800, 6202 AZ Maastricht, Netherlands

* Corresponding author. Tel.: +31 (43) 3875095; fax: +31 (43) 3875104.

Objective: The mechanism of acquired torsade-de-pointes arrhythmias (TdP) is not clear but is suggested to be based on several parameters including early afterdepolarizations (EADs) and/or dispersion of repolarization ({Delta}APD). In our animal model of TdP (anaesthetized dogs with chronic AV block), we assessed the relevance of interventricular dispersion for the initiation of TdP. Methods: In 24 experiments, multiple endocardial monophasic action potential (MAP) recordings were made at baseline, after d-sotalol (2 mg/kg), and after MgSO4 (100 mg/kg, n=11) to measure regional differences in action potential duration (APD). Rate-dependent behavior of the interventricular {Delta}APD (APD of left minus right ventricle) and intraventricular dispersion was studied under the different circumstances. Results: Dogs with induction of TdP by d-sotalol and pacing (11/20=55%) had longer cycle lengths of idioventricular rhythm, longer QT-durations, increased presence of EADs (14/22 vs 5/18 MAPs, P<0.05) and increased interventricular {Delta}APD (135±55 vs 60±40 ms, P<0.05) compared with non-inducible dogs. There were no differences in intraventricular dispersion. MgSO4 diminished {Delta}APD (110±45 to 55±60 ms, P<0.05) and prevented TdP (4/4). In contrast to intraventricular dispersion, interventricular {Delta}APD is clearly bradycardia-dependent. Conclusions: Next to bradycardia, prolonged repolarization, and EADs, we propose that {Delta}APD should be added to the relevant factors for the initiation of TdP. Interventricular dispersion is much larger than intraventricular dispersion and demonstrates a very strong bradycardia dependence.

KEYWORDS Arrhythmias; Monophasic action potential; Early afterdepolarization; Dog, anesthetized; Magnesium


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