BUNDLE BRANCH BLOCKS SIMULATIONS IN VENTRICULAR MODEL WITH REALISTIC GEOMETRY AND CONDUCTION SYSTEM

Abstract

The goal of the study was to design a model of cardiac ventricles with realistic geometry that enables simulation of the ventricular activation with normal conduction system functions, as well as with bundle branch blocks. In ventricles, electrical activation propagates from the His bundle to the left and right bundle branches and continues to the fascicles and branching fibers of the Purkinje system. The role of these parts of the conduction system is to lead the activation rapidly and synchronously to the left and right ventricle. The velocity of propagation in the conduction system is several times higher than in the surrounding ventricular myocardium. If the conduction system works normally, QRS duration representing the total activation time of the ventricles lies in the physiological range of about 80 to 120 ms but it is more than 120 ms in the case of bundle branch blocks. In our study, the realistic geometry of the ventricles was constructed on the base of a patient CT scan, defining epicardial and endocardial surfaces. The first part of the conduction system (fast-conducting bundle branches, fascicles in the left ventricle and initial parts of the Purkinje fibers) was modeled as polyline pathways isolated from the surrounding ventricular tissue. The remaining part of the Purkinje system was modeled as an endocardial layer with higher conduction velocity. The propagation of the electrical activation in the ventricular model was modeled using reaction-diffusion (RD) equations, except for the first part of the conduction system, where the activation times were evaluated algebraically with respect to predefined velocity of propagation and estimated distance between the His bundle and particular entry point to the layer with higher conduction velocity. Propagation of activation in cardiac ventricles was numerically solved in Comsol Multiphysics environment. Several configurations of the first part of the conduction system with different number of polyline pathways and entry points were proposed and tested to achieve realistic activation propagation. For the model with 9 starting points, realistic total activation time (TAT) of the whole ventricles of about 108 ms was obtained for the model with normal conduction system, and realistic TAT of 126 ms and 149 ms were obtained for the right and left bundle branch block (RBBB, LBBB), respectively. Very similar TAT was found also for the model with 7 starting points, but unrealistically long TAT was obtained in LBBB simulation for the model with only 5 starting points.