Effects of electroporation on the transmembrane potential distribution in a two-dimensional bidomain model of cardiac tissue

Electroporation in a Two-Dimensional Myocardium. Introduction: Defibrillation shocks, when delivered through internal electrodes, establish transmembrane potentials (Vm) large enough to electroporate the membrane of cardiac cells. The effects of such shocks on the transmembrane potential distribution are investigated in a two-dimensional rectangular sheet of cardiac muscle modeled as a bidomain with unequal anisotropy ratios. Methods and Results: The membrane is represented by a capacitance Cnv, a leakage conductance gv and a variable electroporation conductance G, whose rate of growth depends exponentially on the square of Vm. The stimulating current Io, 0.05–20 A/m, is delivered through a pair of electrodes placed 2 cm apart for stimulation along fibers and 1 cm apart for stimulation across fibers. Computer simulations reveal three categories of response to Io: (1) Weak Io. below 0.2 A/m, cause essentially no electroporation, and Vm: increases proportionally to Io. (2) Strong Io, between 0.2 and 2.5 A/m, electroporate tissue under the physical electrode. Vm is no longer proportional to Io; in the electroporated region, the growth of Vm is halted and in the region of reversed polarity (virtual electrode), the growth of Vm is accelerated. (3) Very strong Io, above 2.5 A/m, electroporate tissue under the physical and the virtual electrodes. The growth of Vm in ail electroporated regions is halted, and a further increase of Vo: increases both the extent of the electroporated regions and the electroporation conductance G. Conclusion: These results indicate that electroporation of the cardiac membrane plays an important role in the distribution of Vm: induced by defibrillation strength shocks.