Effects of the discrete cellular structure on electrical propagation in cardiac tissue

Abstract

The effects of the discrete cellular structure on propagation of electrical excitation in cardiac muscle were studied in a 1-dimensional fiber model containing a periodic intercalated disc (ID) structure. Globally, the macroscopic velocity of propagation follows the behavior associated with propagation in a continuous tissue (except for high values of disc resistance). In addition, the computed spatial extracellular potential is a smooth bi-phasic waveform and does not reflect the underlying discrete cellular structure of the tissue. Other results of the simulations demonstrate the discontinuous nature of propagation. \({\dot {\text{V}}_{\text{max}}}\) displays a bi-phasic behavior as a function of increasing ID resistance. An initial ‘paradoxical’ increase in \({\dot {\text{V}}_{\text{max}}}\) (with a simultaneous decrease in conduction velocity) is followed by a decrease which leads to decremental propagation and conduction block. The time constant of the foot of the action potential (τfoot) increases monotonically with increasing ID resistance. An increase in the leakage current to extracellular space brings about a significant decrease in the action potential duration and a loss of the plateau. This major effect is accompanied by a relatively smaller decrease in conduction velocity. Collision of two activation wavefronts results in a significant (100%) increase in \({\dot {\text{V}}_{\text{max}}}\) and a very small (0.6%) decrease in τfoot.