Published online before print February 24, 2005, doi: 10.1161/01.RES.0000160709.49633.2b
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© 2005 American Heart Association, Inc.
UltraRapid Communications |
Mechanisms of Atrial Fibrillation Termination by Pure Sodium Channel Blockade in an Ionically-Realistic Mathematical Model
From the Research Center and Department of Medicine, Montreal Heart Institute and University of Montreal (J. Kneller, R.Z., S.N.); the Department of Pharmacology, McGill University (S.N.), Montreal, Quebec, Canada; the Department of Pharmacology and Institute for Cardiovascular Research, SUNY Upstate Medical University (J. Kalifa, A.V.Z., M.W., O.B., J.J.); Syracuse, NY; and the Department of Electrical and Computer Engineering (E.J.V., L.J.L), University of Calgary, Alberta, Canada.
Correspondence to Dr Stanley Nattel, Research Center, Montreal Heart Institute, 5000 Belanger St E, Montreal, Quebec, Canada, H1T 1C8. E-mail stanley.nattel{at}icm-mhi.org
The mechanisms by which Na+-channel blocking antiarrhythmic drugs terminate atrial fibrillation (AF) remain unclear. Classical "leading-circle" theory suggests that Na+-channel blockade should, if anything, promote re-entry. We used an ionically-based mathematical model of vagotonic AF to evaluate the effects of applying pure Na+-current (INa) inhibition during sustained arrhythmia. Under control conditions, AF was maintained by 1 or 2 dominant spiral waves, with fibrillatory propagation at critical levels of action potential duration (APD) dispersion. INa inhibition terminated AF increasingly with increasing block, terminating all AF at 65% block. During 1:1 conduction, INa inhibition reduced APD (by 13% at 4 Hz and 60% block), conduction velocity (by 37%), and re-entry wavelength (by 24%). During AF, INa inhibition increased the size of primary rotors and reduced re-entry rate (eg, dominant frequency decreased by 33% at 60% INa inhibition) while decreasing generation of secondary wavelets by wavebreak. Three mechanisms contributed to INa block–induced AF termination in the model: (1) enlargement of the center of rotation beyond the capacity of the computational substrate; (2) decreased anchoring to functional obstacles, increasing meander and extinction at boundaries; and (3) reduction in the number of secondary wavelets that could provide new primary rotors. Optical mapping in isolated sheep hearts confirmed that tetrodotoxin dose-dependently terminates AF while producing effects qualitatively like those of INa inhibition in the mathematical model. We conclude that pure INa inhibition terminates AF, producing activation changes consistent with previous clinical and experimental observations. These results provide insights into previously enigmatic mechanisms of class I antiarrhythmic drug-induced AF termination. The full text of this article is available online at http://circres.ahajournals.org
Key Words: atrial fibrillation • mathematical model • class I drugs • sodium channels
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