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Ventricular fibrillation and the requirements for fibrillation are theoretically analyzed using a discrete element neighborhood (cellular automation) model of ventricular conduction. The model is configured as a 2500 element rectangular grid on the surface of a cylinder. It is shown that vulnerability to fibrillation is strongly influenced by excited state duration which primarily determines the nature of the underlying reentry activity. As excited state duration is increased fibrillation changes from 'coarse' macroreentrant activity to the more chaotic 'fine' fibrillation sustained by multiple wavelets of microreentry. In general, defibrillation is achieved by a stimulus strong enough to depolarize the majority of relative refractory elements. The threshold for defibrillation is increased for the more irregular microreentrant fibrillation.
Date of Publication: March 1992