Behaviour of the Purkinje system during defibrillation-strength shocks

During normal sinus rhythm, orderly activation of the heart is facilitated by a specialized network of fibres lining the ventricles called the Purkinje system (PS). Characteristic features of the PS encourage coordinated depolarization of spatially disparate endocardial sites. Although the basic role A the PS is well understood, many questions regarding its behaviour, especially during the process of defibrillation, remain unanswered. Purkinje fibres react differently during large electrical shocks than the myocardium on which they run because they are oriented in different directions than the endocardial fibres, they possess distinct electrophysiology, and they are part of a system that is one-dimensional in nature. Because,if the small size of Purkinje fibres and their positioning on the endocardium, in vivo observation of PS-related phenomena remains problematic. Therefore, computer modelling offers a unique opportunity to investigate the role of the PS during defibrillation. In this paper, the effects of defibrillation-strength shocks on a finite element model of the ventricles coupled to a distinct PS are ascertained. Results indicate that the presence of the PS has a profound impact on the course of activation in the ventricles. During shocks, depolarizations are elicited at bends and bifurcations in the PS. Subsequently, this activity spreads throughout the PS in all directions, creating numerous regions of myocardial depolarization and accelerating the excitation A the whole structure. These excitations are explained by the cable-like nature of Purkinje fibres, which exposes them to vastly different electrical field effects than bulk myocardium. due to abrupt conductivity tensor changes. Depending on electrode orientation and the depth of fibre penetration into the endocardium, this phenomenon can bring about a significant abbreviation of the total activation time for a particular shock when compared to simulations where the PS is not included. For a medium-strength shock oriented along the main axis of the heart, the PS produced a 30% reduction in activation time. In conclusion, the PS is of fundamental importance for determining defibrillation shock response.