Chapter 31 – Modeling Cardiac Defibrillation

Despite the large body of research devoted to ventricular defibrillation, the mechanisms by which a strong electric shock delivered to the heart terminates lethal disturbances in ventricular rhythm are still a subject of considerable debate. Experimental evidence strongly suggests 1 2 3 4 5 that the shock induces regions of positive and negative change in transmembrane potential termed virtual electrode polarization ; this evidence is also supported by numeric simulations of the defibrillation process. 6 7 8 9 10 11 The virtual electrode polarization is highly nonuniform and is strongly dependent on the underlying tissue structure. 3 12 13 Cells experiencing this shock-induced change in transmembrane potential rapidly alter the course of their action potential in a nonlinear fashion. The changes in individual cell electrical behavior result in altered overall electrical behavior of the myocardium: certain regions could remain refractory for considerable intervals of time, whereas excitability might be partially or completely restored in others. The outcome of the shock depends on this postshock transmembrane potential distribution, but more importantly, on the spatial interactions that ensue thereafter and the new wave fronts that are elicited as a result of these spatial interactions.

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