Propagation through electrically coupled cells: two inhomogeneously coupled cardiac tissue layers.

Most of the ventricular endocardial surface is covered with a layer of Purkinje (P) cells which provide a rapid spread of activation into the underlying ventricular (V) cells. We have shown experimentally that the P-V junctional region of papillary muscles is spatially inhomogeneous with different regions showing bidirectional conduction, bidirectional block, or unidirectional block between the P and V layers. We have now extended our one-dimensional simulations to a double layer of excitable cells with spatially inhomogeneous electrical coupling between the two layers. Our simulations show that a partial uncoupling can actually increase the common conduction velocity of the two layers and can produce successful P-to-V conduction at regions that would otherwise show P-to-V block, and inhomogeneous spatial distributions of coupling resistivity between two excitable layers can simulate the observed spatial distribution of spatially variable conduction block in papillary muscles. Our simulations indicate that a partial regional electrical coupling may be a useful design feature of the heart to enhance the velocity and safety factor of ventricular activation, but the further increases in uncoupling that may be associated with ischemia may provide a structural basis for the occurrence of arrhythmias.