Action potential propagation in a bidomain model of the discrete Purkinje-ventricular junction

To study electrophysiologic interactions between Purkinje fibers and ventricular myocardium in the region of the Purkinje-ventricular (PV) junction, we developed a modeling strategy that incorporated contemporary descriptions of the histology of the junctional region, membrane ionic currents in Purkinje and myocardial cell types, and current flow between cells in the intracellular, interstitial and extracellular spaces. Models included distinct Purkinje (P), transitional (T) and ventricular (V) cell regions, with individual "connection strands" (P to T and T to V) specified according to the morphological arrangement. Using nominal electrical coupling parameters, electrotonic interactions between the P, T and V cell regions caused multiple focal deflections on waveforms in adjoining regions during the spread of depolarization following P stimulation. While some of those deflections were clearly attributable to discontinuous propagation near the connection strand insertions, waveform deflections at sites away from the insertions resulted from continuous interstitial coupling. Our results suggest a contribution of the interstitium in the interpretation of transmembrane potential recordings from the PV junctional region.