Document Detail


Syncytial heterogeneity as a mechanism underlying cardiac far-field stimulation during defibrillation-level shocks.
MedLine Citation:
PMID:  9581954     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
INTRODUCTION: The mechanisms by which a defibrillation shock directly stimulates regions of cardiac tissue distal to the stimulus electrodes ("far-field" stimulation) are still not well understood. Existing hypotheses have proposed that intercellular discontinuities and/or fiber curvatures induce the requisite membrane polarizations. This article hypothesizes a third potential mechanism: one based on the existence and influences of syncytial (anatomic) heterogeneities inherent throughout the bulk myocardium itself. METHODS AND RESULTS: We simulated the effects of such heterogeneities in a model of a two-dimensional region of passive cardiac tissue subjected to uniform 1 V/cm longitudinal or transverse field stimuli. Heterogeneities were manifested via random spatial variations of intracellular volume fractions (fi) over multiple length scales, with mean fi of 80% and standard deviation of fi (sigma[fi]) ranging from 0% to 10%. During field stimulation, many interspersed and variously shaped and sized islands of hyperpolarization and depolarization developed across the tissue, with their locations and extents correlated to the spatial gradients of the underlying heterogeneities. Increases in sigma(fi) correspondingly increased the shock-induced magnitudes of resulting membrane polarizations. The ratio of maximal polarizations for equivalent longitudinal and transverse shocks approximated 2:1 across all sigma(fi) tested. At sigma(fi) = 5%, these maximal induced polarizations were 17.4 +/- 2.4 mV and 8.18 +/- 1.5 mV, respectively. Assuming an excitation threshold of 25 mV, these data suggest corresponding diastolic thresholds of 1.47 +/- 0.20 V/cm and 3.14 +/- 0.50 V/cm, respectively. CONCLUSION: This study predicts that syncytial heterogeneities inherent within cardiac tissue could represent a significant-and heretofore unappreciated-mechanism underlying field-induced polarizations throughout the bulk myocardium.
Authors:
M G Fishler
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of cardiovascular electrophysiology     Volume:  9     ISSN:  1045-3873     ISO Abbreviation:  J. Cardiovasc. Electrophysiol.     Publication Date:  1998 Apr 
Date Detail:
Created Date:  1998-06-05     Completed Date:  1998-06-05     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  9010756     Medline TA:  J Cardiovasc Electrophysiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  384-94     Citation Subset:  IM    
Affiliation:
St. Jude Medical CRMD, Sunnyvale, California 94086, USA. mfishler@ventritex.com
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MeSH Terms
Descriptor/Qualifier:
Arrhythmias, Cardiac / physiopathology,  prevention & control*
Computer Simulation
Electric Countershock*
Heart / physiopathology*
Membrane Potentials
Models, Biological*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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