Analysis of the Impact of Fusion Beats onto Epicardial Electrograms based on a Bidomain Slab Model

Abstract

Fusion Beats caused by ventricular multi-site pacing are utilized for therapeutic treatments. They can also result from pacing applied during the spreading of spontaneous excitation before they are sensed. Such non-intended fusion beats are suspected to reduce the hemodynamic efficiency and, hence should be prevented by proper pacing. To improve the understanding how the signal morphology of recorded electrograms are affected by fusion beats, a three dimensional bidomain slab model has been developed. The slab model is considered approximating a ventricular free wall and comprise transmural fiber rotation to simulate the anisotropic conductivity conditions and action potential heterogeneity. Extracellular currents were injected near the center of the epicardium to induce an activation sequence mimicking a paced event. Spontaneous excitations via the Purkinje fiber system were simulated by a superimposed cellular automaton near the endocardial surface. The interaction between the different proceeding excitation waves reflect in the depolarization as well as the repolarization period, therefore an entire action potential cycle was simulated. The main pattern of the simulated extracellular potential course was compared with recorded signals from pacemaker patients with epicardial implanted electrodes.