Re - entrant excitation initiated in models of inhomoge - neous atrial

We demonstrate that a shift of the vulnerable window caused by tissue inhomogeneity can play a role in the generation of reentrant excitation. The Earm-Hilgemann-Noble equations were incorporated into 1and 2-dimensional inhomogeneous partial di erential equation models of atrial tissue. Inhomogeneity was produced by a reduction of gNa over part of the medium and the vulnerable window for initiating re-entrant activity in homogeneous models determined from numerical integrations. Reduction of gNa 40% produced little e ect on the width of the vulnerable window, but the onset of the vulnerable window was delayed. The delay of the vulnerable window allows re-entry to be initiated at junction between media with normal and reduced excitability, even though there is no appreciable change in action potential duration.