Defibrillation threshold computed from normal and supernormal excitable cardiac tissue.

The applicability of the 'upper limit of vulnerability' defibrillation theory was evaluated in models of cardiac tissue in which spatial changes within cells are retained. Defibrillation thresholds were computed from two models of cardiac tissue: one with, and one without, a supernormal period, and compared with those predicted by the theory. In the cardiac virtual tissue with a monotonic recovery of excitation - a normal refractory period, the computed defibrillation threshold is consistent with the prediction of the 'upper limit of vulnerability' defibrillation theory. However, in cardiac tissue with non-monotonic recovery of excitation - a supernormal period, the computed defibrillation threshold is significantly less than the theory prediction.