The Shock Energy Required for Successful Defibrillation Depends on the Degree of Disorganization of the Reentrant Activation Pattern

Abstract

Regardless of how it is initiated, the final stage of sudden cardiac death is ventricular fibrillation (VF), a completely disorganized electrical activity of the ventricles, characterized by multiple reentrant circuits. There is only one known therapy for VF, a strong electrical shock, normally referred to as electrical defibrillation. In this study we investigate the hypothesis that the energy level required to stop fibrillation is dependent on the actual level of organization of the underlying reentrant activity. A three-dimensional bidomain model with unequal anisotropy ratios incorporating stochastic variations of the conductivity tensor was used. The active membrane behavior was described by the Courtemanche model of the human atrial action potential incorporating an acetylcholin (ACh) dependent K ⁺ current and electroporation. A spatial variation of [ACh] was used to obtain repolarization gradients allowing to control the degree of disorganization. Depending on the ACh settings, either a single rotor developed or spiral wave breakup evolving into fibrillatory like activity was observed. Shocks of varying strength and timing were delivered to both activation patterns and the probability of shock success as a function of shock strength was determined. Results indicate that arrhythmias with a higher degree of disorganization need significantly higher shock strengths to defibrillate.