EFFECTS OF NONUNIFORM SLOWING OF CONDUCTION ON VULNERABILITY TO FIBRILLATION IN A COMPUTER-MODEL

Introduction: Effects of conduction defects on vulnerability to fibrillation are difficult to evaluate experimentally because interventions to produce defects are also likely to affect recovery of excitability. Methods and Results: To evaluate effects, a computer model in which recovery characteristics and conduction defects in the form of slowed propagation could be independently varied was used. Findings showed that conduction defects increased vulnerability but the magnitude of effects depended on the characteristics of recovery with which defects were combined. Fibrillation threshold was most markedly decreased by conduction defects when the range of recovery properties that together with cycle lengths determined refractory periods was low or the mean value of recovery properties was high. The mechanism was increased nonuniformity of propagation. This was shown to increase with successive premature responses so conduction defects had an increasing effect on fibrillation threshold as the number of responses required to initiate fibrillation increased. It has been previously shown that mean recovery property value affects the number of premature responses possible per unit time while recovery property range affects the degree of nonuniform propagation per premature response. New evidence in this study showed that in addition to these effects, decreasing mean and increasing range of recovery properties decreased the degree of nonuniform propagation required to initiate fibrillation. Fewer premature responses were therefore required and effects of conduction defects were small. Conclusions: Findings suggest that the importance of conduction defects to vulnerability depends on coexisting characteristics of recovery.