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Optimisation of ionic models to fit tissue action potentials: application to 3D atrial modelling.

Al Abed A, Guo T, Lovell NH, Dokos S - Comput Math Methods Med (2013)

Bottom Line: A 3D model of atrial electrical activity has been developed with spatially heterogeneous electrophysiological properties.Membrane potentials of myocytes from spontaneously active or electrically paced in vitro rabbit cardiac tissue preparations were recorded using intracellular glass microelectrodes.The tissue-based optimisation of ionic models and the modelling process outlined are generic and applicable to image-based computer reconstruction and simulation of excitable tissue.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Biomedical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. amra@unsw.edu.au

ABSTRACT
A 3D model of atrial electrical activity has been developed with spatially heterogeneous electrophysiological properties. The atrial geometry, reconstructed from the male Visible Human dataset, included gross anatomical features such as the central and peripheral sinoatrial node (SAN), intra-atrial connections, pulmonary veins, inferior and superior vena cava, and the coronary sinus. Membrane potentials of myocytes from spontaneously active or electrically paced in vitro rabbit cardiac tissue preparations were recorded using intracellular glass microelectrodes. Action potentials of central and peripheral SAN, right and left atrial, and pulmonary vein myocytes were each fitted using a generic ionic model having three phenomenological ionic current components: one time-dependent inward, one time-dependent outward, and one leakage current. To bridge the gap between the single-cell ionic models and the gross electrical behaviour of the 3D whole-atrial model, a simplified 2D tissue disc with heterogeneous regions was optimised to arrive at parameters for each cell type under electrotonic load. Parameters were then incorporated into the 3D atrial model, which as a result exhibited a spontaneously active SAN able to rhythmically excite the atria. The tissue-based optimisation of ionic models and the modelling process outlined are generic and applicable to image-based computer reconstruction and simulation of excitable tissue.

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Setup of 2D disc models. (a) 2D disc approximation of the human SAN and surrounding atrial tissue. (b) 1D cable representation of 2D axisymmetric disc. AP waveforms at shown selected nodes representing cSAN, pSAN, and atrial tissue were optimised. (c) 1D cable representation of an LA-PV disc.
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fig3: Setup of 2D disc models. (a) 2D disc approximation of the human SAN and surrounding atrial tissue. (b) 1D cable representation of 2D axisymmetric disc. AP waveforms at shown selected nodes representing cSAN, pSAN, and atrial tissue were optimised. (c) 1D cable representation of an LA-PV disc.

Mentions: In order to better account for the electrotonic interaction between myocytes, a 1D numerical approximation of an axisymmetric heterogeneous 2D disc model of electrical propagation was developed based on the generic ionic model described above and a modified form of the cable equation [20](7)∂∂r(rσb2∂Em∂r)=rIm,where σ (μS·cm−1) is the tissue conductivity, r (cm) is the distance from the centre of the disc, b = 2 × 10−3 (cm) is the disc thickness, assuming it is one cell layer thick, and Im (nA·cm−2) is the total membrane current, comprised of capacitive and ionic components according to(8)Im=CmdEmdt+IL+∑j=1NIj,where all the variables are as defined in (1). To represent myocyte heterogeneity in the atrium, the cable was divided into the appropriate number of sections, each with its distinct tissue conductivity value and ionic model parameters. Two axisymmetric discs were considered: one representing a right atrial preparation comprised of a central SAN (cSAN) region, a peripheral SAN (pSAN) region, and surrounding right atrium (RA), and the other representing a left atrial preparation comprised of left atrium (LA) and a pulmonary vein (PV) region. These two disc models will be referred to as cSAN-pSAN-RA and LA-PV, respectively (Figure 3). The tissue conductivity was selected to produce known conduction velocity (CV) in each segment: 20–30 cm·s−1 in the central and peripheral regions of the SAN and 80–100 cm·s−1 in the right and left atria. APs generated at selected points from each section of the cable were fitted to APs recorded experimentally from the corresponding intact myocyte by optimising the ionic model parameters assigned to that particular section of the disc.


Optimisation of ionic models to fit tissue action potentials: application to 3D atrial modelling.

Al Abed A, Guo T, Lovell NH, Dokos S - Comput Math Methods Med (2013)

Setup of 2D disc models. (a) 2D disc approximation of the human SAN and surrounding atrial tissue. (b) 1D cable representation of 2D axisymmetric disc. AP waveforms at shown selected nodes representing cSAN, pSAN, and atrial tissue were optimised. (c) 1D cable representation of an LA-PV disc.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3713319&req=5

fig3: Setup of 2D disc models. (a) 2D disc approximation of the human SAN and surrounding atrial tissue. (b) 1D cable representation of 2D axisymmetric disc. AP waveforms at shown selected nodes representing cSAN, pSAN, and atrial tissue were optimised. (c) 1D cable representation of an LA-PV disc.
Mentions: In order to better account for the electrotonic interaction between myocytes, a 1D numerical approximation of an axisymmetric heterogeneous 2D disc model of electrical propagation was developed based on the generic ionic model described above and a modified form of the cable equation [20](7)∂∂r(rσb2∂Em∂r)=rIm,where σ (μS·cm−1) is the tissue conductivity, r (cm) is the distance from the centre of the disc, b = 2 × 10−3 (cm) is the disc thickness, assuming it is one cell layer thick, and Im (nA·cm−2) is the total membrane current, comprised of capacitive and ionic components according to(8)Im=CmdEmdt+IL+∑j=1NIj,where all the variables are as defined in (1). To represent myocyte heterogeneity in the atrium, the cable was divided into the appropriate number of sections, each with its distinct tissue conductivity value and ionic model parameters. Two axisymmetric discs were considered: one representing a right atrial preparation comprised of a central SAN (cSAN) region, a peripheral SAN (pSAN) region, and surrounding right atrium (RA), and the other representing a left atrial preparation comprised of left atrium (LA) and a pulmonary vein (PV) region. These two disc models will be referred to as cSAN-pSAN-RA and LA-PV, respectively (Figure 3). The tissue conductivity was selected to produce known conduction velocity (CV) in each segment: 20–30 cm·s−1 in the central and peripheral regions of the SAN and 80–100 cm·s−1 in the right and left atria. APs generated at selected points from each section of the cable were fitted to APs recorded experimentally from the corresponding intact myocyte by optimising the ionic model parameters assigned to that particular section of the disc.

Bottom Line: A 3D model of atrial electrical activity has been developed with spatially heterogeneous electrophysiological properties.Membrane potentials of myocytes from spontaneously active or electrically paced in vitro rabbit cardiac tissue preparations were recorded using intracellular glass microelectrodes.The tissue-based optimisation of ionic models and the modelling process outlined are generic and applicable to image-based computer reconstruction and simulation of excitable tissue.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Biomedical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. amra@unsw.edu.au

ABSTRACT
A 3D model of atrial electrical activity has been developed with spatially heterogeneous electrophysiological properties. The atrial geometry, reconstructed from the male Visible Human dataset, included gross anatomical features such as the central and peripheral sinoatrial node (SAN), intra-atrial connections, pulmonary veins, inferior and superior vena cava, and the coronary sinus. Membrane potentials of myocytes from spontaneously active or electrically paced in vitro rabbit cardiac tissue preparations were recorded using intracellular glass microelectrodes. Action potentials of central and peripheral SAN, right and left atrial, and pulmonary vein myocytes were each fitted using a generic ionic model having three phenomenological ionic current components: one time-dependent inward, one time-dependent outward, and one leakage current. To bridge the gap between the single-cell ionic models and the gross electrical behaviour of the 3D whole-atrial model, a simplified 2D tissue disc with heterogeneous regions was optimised to arrive at parameters for each cell type under electrotonic load. Parameters were then incorporated into the 3D atrial model, which as a result exhibited a spontaneously active SAN able to rhythmically excite the atria. The tissue-based optimisation of ionic models and the modelling process outlined are generic and applicable to image-based computer reconstruction and simulation of excitable tissue.

Show MeSH
Related in: MedlinePlus