How ischaemic region shape affects ST potentials in models of cardiac tissue

Abstract

This numerical study uses a simple bidomain model of cardiac tissue to compare the effect of three different ischaemic region geometries (rectangular, cylindrical and semi-ellipsoidal) on the extracellular epicardial potentials during the ST segment. Results are obtained using anisotropic conductivities based on experimentally derived data. The model is then altered, to include heterogeneous conductivities in the ischaemic region and larger border zone widths, in order to better reproduce realistic scenarios. Initial results for the rectangular and cylindrical ischaemic shapes show a central depression over the ischaemic region, for low ischaemic thicknesses, which separates into three depressions as the ischaemic thickness increases. For ischaemic thicknesses above 70% an elevation appears over the ischaemic region and this increases in magnitude as the ischaemia becomes transmural. Results for the semi-ellipsoidal shape, however, differ, with the central depression separating into only two depressions as the thickness increases. Changing the conductivity inside the ischaemic region significantly affects results for each geometry, with depression staying over the ischaemic region for much higher levels of ischaemia (up to 90% thickness). Increasing the intramural border zone thickness did not significantly affect the epicardial potential distributions.

Sensitivity analysis of ST-segment epicardial potentials arising from changes in ischaemic region conductivities in early and late stage ischaemia

“…This work has investigated the role that input parameters play in determining the type of potential distributions that are generated, by subendocardial ischaemia, on the epicardial surface, during the ST segment of the ECG. A number of recent modelling studies [7,8,35,16,36,2,5,6,9,10] have investigated this, using various modelling assumptions and values for the model inputs. This study has extended this work in a number of different directions: we modelled both early and late stage ischaemia and considered all six bidomain conductivities; we varied the ischaemic region conductivities independently of those in the remainder of the tissue, and, using UQ, we were able to systematically consider the effect of the model inputs on the EPDs.…”

“…where a 1 = 0.9, b 1 = 0.2, b 2 = 0.01, a 2 = 0.1 and Ψ 2 replaces Ψ 1 in equation (5) in the t = θ and φ directions (see Figure 3). To solve the model, we apply the same boundary conditions as previously [27,10]; that is, it is assumed that there is no current flux at the boundaries of the intra-and extracellular domains, nor at the blood-air and tissue-air interfaces, and that the extracellular current and potential are continuous at the blood-tissue boundary.…”

“…Connecting this work to the ECG would then require the addition of a torso model. These modelling studies have examined aspects such as the size, shape and location of the ischaemic region [2,3,4,5], cardiac volume variability [6] and the effect of cardiac anisotropy [7,8,2,9,10].…”

Using Generalised Polynomial Chaos to Examine Various Parameters in a Half-ellipsoidal Ventricular Model of Partial Thickness Ischaemia

“…slabs, cylinders, half-ellipsoids [1]), while other work uses more realistic geometries [2,3]. Another study [4] has looked at the effect of the shape of the ischaemic region on the epicardial potential distributions (EPDs) that are produced.…”

“…slabs, cylinders, half-ellipsoids [1]), while other work uses more realistic geometries [2,3]. Another study [4] has looked at the effect of the shape of the ischaemic region on the epicardial potential distributions (EPDs) that are produced.The majority of recent work represents the cardiac tissue as consisting of interpenetrating bi-domains, intracellular (i) and extracellular (e). In these the current is assumed to flow in three mutually orthogonal directions, longitudinal (l), transverse (t) and normal (n), that is along, across and between the sheets of cardiac fibres, respectively.…”