Session S43.4

Optimal Safety of Conduction through the Purkinje-Ventricular Junction

P Stewart*, OV Aslanidi, MR Boyett, H Zhang

The University of Manchester
Manchester, UK

Slow and discontinuous action potential (AP) conduction through non-uniform junctions in cardiac tissues is believed to be unsafe and pro-arrhythmogenic, as it may lead to local AP conduction failure and ultimately reentrant excitation. We studied AP conduction through the Purkinje-ventricular junction (PVJ) to address a fundamental issue of the relationship between the tissue structure and electrical heterogeneity, and the AP conduction velocity and safety.
We coupled a 3D anatomically and electrophysiologically detailed model of a canine ventricular wedge with a single Purkinje fiber (PF) connected to the endocardium. The intercellular electrical coupling in the PF and ventricular tissues was set to produce experimentally observed AP conduction velocities of ~1.8 and 0.5 m/s, respectively. Thickness, d, and the diffusion coefficient, D, of the PF were varied in order to determine optimal conditions (velocity, v, and safety factor, SF) of the AP conduction through the PVJ.
The AP conduction from PF through the anatomically and electrically non-uniform PVJ was discontinuous with a time delay of ~5 ms. Dependence of SF on d showed a maximum at ~1 mm, and dependence of SF on v had a maximum at ~0.3 m/s, which corresponded to an optimal velocity providing the maximum safety of AP conduction through the PVJ. Dependence of SF on D showed a maximum at ~1.5 mm^2/ms, and the respective dependence of SF on v in this case had a maximum at ~0.6 m/s.
In summary, we found that: (1) the experimentally observed conduction time delay across the junction was a natural consequence of the electrophysiological and morphological differences between the two tissue types; (2) neither very fast nor very slow AP conduction was safe, leading to an optimal velocity providing the maximum SF of conduction through the PVJ.

(Abstract Control Number: 116)