Cardiac microimpedance measurement in two-dimensional models using multisite interstitial stimulation

Abstract

. Cardiac microimpedance measurement in two-dimensional models using multisite interstitial stimulation. Am J Physiol Heart Circ Physiol 290: H1976 -H1987, 2006. First published December 22, 2005 doi:10.1152/ajpheart.01180.2005.-We analyzed central interstitial potential differences during multisite stimulation to assess the feasibility of using those recordings to measure cardiac microimpedances in multidimensional preparations. Because interstitial current injected and removed using electrodes with different proximities allows modulation of the portion of current crossing the membrane, we hypothesized that multisite interstitial stimulation would give rise to central interstitial potential differences that depend on intracellular and interstitial microimpedances, allowing measurement of those microimpedances. Simulations of multisite stimulation with fine and wide spacing in two-dimensional models that included dynamic membrane equations for guinea pig ventricular myocytes were performed to generate test data ‫ץ(‬ o). Isotropic interstitial and intracellular microimpedances were prescribed for one set of simulations, and anisotropic microimpedances with unequal ratios (intracellular to interstitial) along and across fibers were prescribed for another set of simulations. Microimpedance measurements were then obtained by making statistical comparisons between ‫ץ‬ o values and interstitial potential differences from passive bidomain simulations (⌬ o) in which a wide range of possible microimpedances were considered. Possible microimpedances were selected at 25% increments. After demonstrating the effectiveness of the overall method with microimpedance measurements using one-dimensional test data, we showed microimpedance measurements within 25% of prescribed values in isotropic and anisotropic models. Our findings suggest that development of microfabricated devices to implement the procedure would facilitate routine measurement as a component of cardiac electrophysiological study. bidomain modeling; virtual electrode; simulation; ventricular myocyte MATHEMATICAL MODELING of cardiac electrical activity has provided important insights into mechanisms for arrhythmia initiation, maintenance, and termination. Since the presentation of the landmark phase II membrane equations by Luo and Rudy in 1994 (33), detailed representations of sarcolemmal currents, ion diffusion, excitation-contraction coupling, and intracellular signaling have been systematically integrated into species-, disease-, and region-dependent mathematical models for the isolated myocyte (1,3,36,37,41,52,59). The detail in these membrane equations is a consequence, primarily, of the extensive quantitative data available from single-cell electrophysiological studies. Strategies for careful positioning of myocytes with cellular and subcellular resolution into structural models have also been described. Resulting meshes incorporate details of the cellular architecture available from histological (22, 50, 53) and imaging (43, 49, 56) data.Specification o...

Laminar Arrangement of Ventricular Myocytes Influences Electrical Behavior of the Heart

“…7,8,33,34 Importantly, although these latest works focus on elegant resolution of the intra-and extracellular conductivities, they seek to determine conductivity on myofiber and "transverse" axes alone, neglecting the effects of the laminar architecture of myocardium. On the cardiac surfaces transverse coupling of myocytes is uniform, however the effects of intramural laminar discontinuities in coupling need to be evaluated with respect to these electrode designs.…”

“…[1][2][3][4][5][6][7][8] Electrical conductivity is thought to be greatest along the myocyte axis allowing most rapid propagation of electrical activation in this direction, and conductivity is commonly assumed to be isotropic transverse to the myocyte axis supporting a slower uniform spread of activation in this plane. [1][2][3][4][5][6][7][8] In this context, knowledge of conductivity in two directions, parallel and transverse to the myofiber axis, is thought sufficient to characterize the electrical action of the heart. This view informs much of the current understanding of cardiac electrophysiology and provides the foundation for interpreting a range of complex phenomena including ventricular fibrillation initiation, maintenance, and termination.…”

Design of a multi-electrode array to measure cardiac conductivities

“…More recent extensions of these measuring techniques often involve arrays of electrodes, where the design of the array is based on the four electrode technique [17,2,20,21,22,9,13,12,14,6]. An example of one of these designs is an array of plunge electrodes [9,10,7,3] that demonstrated that porcine ventricular tissue is electrically orthotropic, with three distinct propagation directions.…”

Analysis of Electrode Configurations for Measuring Cardiac Tissue Conductivities and Fibre Rotation

“…7 This work has been extended to use two-dimensional models. 22 Possible practical difficulties associated with these systems include the requirement for tiny electrodes and micrometre electrode spacings 2 and the precision required in manufacturing and calibrating these small electrode systems. 23 It has previously been demonstrated, by Hofer et al 6 and Kim et al, 11 that it is possible to use microfabricated arrays to record electrograms in superfused guinea pig and perfused mouse and rabbit papillary muscle preparations.…”

“…Such studies suggest that the use of microfabricated arrays with micrometre spacing is technically feasible. 22 In order to recover the cardiac parameters from potential measurements, it is necessary to use a cardiac tissue model. This paper makes use of a previously presented 9 mathematical bidomain model, which is able to include the effects of fibre rotation.…”