Active response of a one-dimensional cardiac model with gap junctions to extracellular stimulation.

To study the response of cardiac tissue to electrical stimulation, a one-dimensional model of cardiac tissue has been developed using linear core-conductor theory and the DiFrancesco-Noble model of Purkinje tissue. The cable lies in a restricted extracellular medium and includes a representation of the junctional resistances known to interconnect cardiac cells. Two electrode geometries are considered: (a) a semi-infinite cable with a monopolar electrode at the end of the cable and (b) a terminated cable with one electrode at each end of the cable. In a series of simulations, stimuli of varying magnitude and polarity are applied at three different times during the plateau of the action potential. The results at the stimulus site show that the action potential duration may either decrease or increase in response to the stimulus, depending on the polarity and application time of the stimulus. The spatial behaviour of the cable in response to the stimulus indicates that sites greater than 200 cells from the stimulating electrode are not affected by the stimulus.