Simulation of triggered secondary repolarization at the junction between normal and depressed cardiac tissue

The authors used a one-dimensional core-conductor model to simulate propagation across the transition zone between normal and depressed myocardium. Normal cells were represented by a modified Beeler-Reuter model. In depressed cells, the nominal extracellular K concentration and time-independent K conductance were increased twofold and the intracellular resistivity was made four times larger. These characteristics and the corresponding resting membrane potential changed progressively across the transition zone, over a distance of about 2 mm. Triggered secondary repolarization results from slow conduction across the transition zone and through the early part of the depressed segment. The phenomenon is initiated by a reduced inward Na current which triggers a regenerative decrease in the secondary inward current just behind the propagating activation front. The result is a localized and progressively expanding zone of fully recovered excitability during the early plateau phase of the action potential