Role of fiber structure-dependent electrically induced membrane polarizations in proarrhythmic early epicardial activations

Although electrical defibrillation has been performed for a century, the interaction between the cardiac tissue and the applied electrical shocks is still largely unknown. The work presented in this dissertation was done to better understand the interaction of cardiac fiber structure with an epicardially applied electrical shock. The goals of this research were to evaluate the role of fiber structure on the effective epicardial resistance of intact ventricles as well as on the shock-induced changes in transmembrane potential that lead to arrhythmia induction.; To examine the role of fiber structure on the effective resistance, the resistance of intact ventricles was measured on the epicardium of isolated rabbit hearts at angles ranging from 0° to 90° with respect to epicardial fibers. The effective resistance was isotropic for all angles. Finite element analysis was performed to explore the influence of fiber rotation in the deeper layers of the myocardium on the effective resistance. Results showed that the multifiber structure in which fibers rotate in deeper layers causes the effective epicardial resistance to be isotropic.; To examine the shock-induced changes in transmembrane potential that lead to arrhythmia induction, we performed line stimulation 45° and 90° with respect to epicardial fibers at various times during the action potential to evaluate whether stimulation produces adjacent regions of positive and negative virtual electrodes and arrhythmias. In cases in which arrhythmias occurred, we tested whether the arrhythmias were spatially related to the virtual electrodes. Line stimulation at both orientations produced adjacent regions of positive and negative electrodes for line stimulation early (phase 2) and late (phase 3) in the action potential. The line stimulation-induced arrhythmias were spatially related to the virtual electrodes.; The findings of this research illustrate the importance of accounting for the complex structure of cardiac tissue in measurements of resistance. The findings also emphasize the importance of the orientation of line electrodes with respect to fibers during stimulation. This work could have implications for applications in which a linear electrode is used to administer electrical stimulation therapy.