Refractory gradient is responsible for the increase in ventricular vulnerability under sodium channel blockade

Background Previous studies have shown that sodium channel (I-Na) blockade increases ventricular vulnerability: however, there were differences in the degree of the increase. Because the vulnerable window (VW) is altered by the type of preshock refractory gradient (RG), the hypothesis was that the differences in the arrhythmogenesis 4 I-Na blockade result from the different types of preshock RG employed. Methods and Results Simulations of regional electric shock following constant pacing stimuli in 2-dimensional bidomain myocardial sheets under I-Na blockade were conducted using 3 types of preshock RG: longitudinally tilted (LRG), transversely tilted (TRG), and non-tilted RG (NRG). The increase in the degree Of I-Na blockade almost linearly decreased the conduction velocity. The action potential duration in the LRG and TRG cases was non-linearly shortened with the increase in I-Na blockade because of electrotonic influences, whereas in the case of NRG it was slightly prolonged. In both LRG and TRG cases, the VW for reentry induction by electric shock was considerably widened by the I-Na blockade; however, this was not the case for NRG in which the VW was rather narrowed by the I-Na blockade. Conclusion The type of preshock RG alters the degree of the increase in ventricular vulnerability under I-Na blockade.