Electric and magnetic fields from two-dimensional anisotropic bisyncytia

Sepulveda, N.G.; Wikswo, Jr Jp

doi:10.1016/s0006-3495(87)83381-7

Cited by 59 publications

(21 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the setting of nonuniform field stimulation, unequal anisotropy between intracellular and extracellular spaces can by itself generate virtual electrodes in the form of a dog-bone shape of polarization, with adjacent regions of opposite polarization. 32 It is interesting to note that the experimental studies confirming these patterns have been carried out on the epicardial surface of the heart, 36 where coupling between myocytes is increased with respect to the midwall, and large intercellular clefts are absent. It is yet to be seen whether a dog-bone pattern of polarization is in fact visible at all, deep within the midwall, during nonuniform field application.…”

Section: Implications For Defibrillationmentioning

confidence: 85%

“…"Virtual electrode" is now common jargon to refer to any site of shock-induced transmembrane potential change distant from the site of current injection. It has been shown that virtual electrodes may be induced by unequal anisotropy of intracellular and extracellular spaces, 32 myofiber curvature, 33 fiber narrowing, 34 spatial inhomogeneity of intracellular volume fraction, 16 and discontinuity associated with gap junctions 15 and intercellular clefts. 13 Any geometrical condition that induces current redistribution across the cell membrane during stimulation will lead to formation of a virtual electrode.…”

Section: Implications For Defibrillationmentioning

confidence: 99%

See 1 more Smart Citation

Cardiac Microstructure

Hooks

Tomlinson

Marsden

et al. 2002

Circulation Research

222

View full text Add to dashboard Cite

Abstract-Our understanding of the electrophysiological properties of the heart is incomplete. We have investigated two issues that are fundamental to advancing that understanding. First, there has been widespread debate over the mechanisms by which an externally applied shock can influence a sufficient volume of heart tissue to terminate cardiac fibrillation. Second, it has been uncertain whether cardiac tissue should be viewed as an electrically orthotropic structure, or whether its electrical properties are, in fact, isotropic in the plane orthogonal to myofiber direction. In the present study, a computer model that incorporates a detailed three-dimensional representation of cardiac muscular architecture is used to investigate these issues. We describe a bidomain model of electrical propagation solved in a discontinuous domain that accurately represents the microstructure of a transmural block of rat left ventricle. From analysis of the model results, we conclude that (1) the laminar organization of myocytes determines unique electrical properties in three microstructurally defined directions at any point in the ventricular wall of the heart, and (2)

show abstract

Section: Implications For Defibrillationmentioning

confidence: 85%

Section: Implications For Defibrillationmentioning

confidence: 99%

Cardiac Microstructure

Hooks

Tomlinson

Marsden

et al. 2002

Circulation Research

222

View full text Add to dashboard Cite

show abstract

“…The difference in the ratios of electrical conductivities parallel and perpendicular to the fiber direction in the intracellular and interstitial spaces, also called "unequal anisotropy ratios," causes the formation of virtual electrodes (39,48). The bidomain model incorporates this feature of cardiac tissue explicitly (37,41,42,47). During anodal stimulation, a dog bone-shaped region of hyperpolarization, oriented transverse to the fiber direction, arises centrally around the stimulating electrode.…”

mentioning

confidence: 99%

Examination of stimulation mechanism and strength-interval curve in cardiac tissue

Sidorov¹,

Woods²,

Baudenbacher³

et al. 2005

American Journal of Physiology-Heart and Circulatory Physiology

View full text Add to dashboard Cite

Understanding the basic mechanisms of excitability through the cardiac cycle is critical to both the development of new implantable cardiac stimulators and improvement of the pacing protocol. Although numerous works have examined excitability in different phases of the cardiac cycle, no systematic experimental research has been conducted to elucidate the correlation among the virtual electrode polarization pattern, stimulation mechanism, and excitability under unipolar cathodal and anodal stimulation. We used a high-resolution imaging system to study the spatial and temporal stimulation patterns in 20 Langendorff-perfused rabbit hearts. The potential-sensitive dye di-4-ANEPPS was utilized to record the electrical activity using epifluorescence. We delivered S1-S2 unipolar point stimuli with durations of 2-20 ms. The anodal S-I curves displayed a more complex shape in comparison with the cathodal curves. The descent from refractoriness for anodal stimulation was extremely steep, and a local minimum was clearly observed. The subsequent ascending limb had either a dome-shaped maximum or was flattened, appearing as a plateau. The cathodal S-I curves were smoother, closer to a hyperbolic shape. The transition of the stimulation mechanism from break to make always coincided with the final descending phase of both anodal and cathodal S-I curves. The transition is attributed to the bidomain properties of cardiac tissue. The effective refractory period was longer when negative stimuli were delivered than for positive stimulation. Our spatial and temporal analyses of the stimulation patterns near refractoriness show always an excitation mechanism mediated by damped wave propagation after S2 termination.

show abstract

“…In fact, virtual electrodes have been found to be induced by unequal anisotropy of intracellular and extracellular spaces (Sepulveda and Wikswo 1987), myofiber curvature (Trayanova and Skouibine 1998), fiber narrowing (Sobie et al 1997), spatial inhomogeneity of intracellular volume fraction(Trayanova 1999), discontinuity associated with gap junctions, and intercellular clefts (Fast et al 1998). The primary issue of concern in this paper is how different spatial distributions of sources and sinks affects the outcome of a defibrillatory shock.…”

Section: Modeling Defibrillationmentioning

confidence: 99%

The effect of spatial scale of resistive inhomogeneity on defibrillation of cardiac tissue

Keener

Cytrynbaum

2003

Journal of Theoretical Biology

View full text Add to dashboard Cite

Defibrillation of cardiac tissue can be viewed in the context of dynamical systems theory as the attempt to move a dynamical system from the basin of attraction of one attractor (fibrillation) to another (the uniform rest state) by applying a stimulus whose form is physically constrained. Here we give an introduction to the physical mechanism of cardiac defibrillation from this dynamical perspective and examine the role of resistive inhomogeneity on defibrillation efficacy. Using numerical simulations with rotating waves on a one-dimensional periodic ring, we study the role of the spatial scale of resistive inhomogeneity on defibrillation.For a rotating wave on a periodic ring there are three stable attractors, namely the uniform rest state, a wave traveling clockwise and a wave traveling counterclockwise. As a result, the application of a stimulus has the potential for three different outcomes, namely elimination of the wave, phase resetting of the wave, and reversal of the wave.The results presented here show that with resistive inhomogeneities of large spatial scale, all three of these transitions are possible with large amplitude shocks, so that the probability of defibrillation is bounded well below one, independent of stimulus amplitude. On the other hand, resistive inhomogeneities of small spatial scale produce a defibrillation threshold that is qualitatively consistent with that found experimentally, namely the probability of defibrillation success is an increasing function that approaches one for large enough stimulus amplitude.Extending these results to higher dimensions, we describe conditions for successful defibrillation of functional reentry with large scale spatial inhomogeneity, but find that elimination of anatomical reentry is quite difficult. With small spatial scale inhomogeneity, there are no similar restrictions. Acknowledgment: This research was supported in part by NSF Grant DMS-99700876 and DMS-0211366. We acknowledge N. Trayanova for clarifying several misconceptions we had concerning her work, and S. Folias for valuable discussions and numerical simulations.

show abstract

Electric and magnetic fields from two-dimensional anisotropic bisyncytia

Cited by 59 publications

References 17 publications

Cardiac Microstructure

Cardiac Microstructure

Examination of stimulation mechanism and strength-interval curve in cardiac tissue

The effect of spatial scale of resistive inhomogeneity on defibrillation of cardiac tissue

Contact Info

Product

Resources

About