Mechanisms of Defibrillation

Abstract

Electrical shock has been the one effective treatment for ventricular fibrillation for several decades. With the advancement of electrical and optical mapping techniques, histology, and computer modeling, the mechanisms responsible for defibrillation are now coming to light. In this review, we discuss recent work that demonstrates the various mechanisms responsible for defibrillation. On the cellular level, membrane depolarization and electroporation affect defibrillation outcome. Cell bundles and collagenous septae are secondary sources and cause virtual electrodes at sites far from shocking electrodes. On the whole-heart level, shock field gradient and critical points determine whether a shock is successful or whether reentry causes initiation and continuation of fibrillation.

The influence of cell dimensions on the vulnerability of ventricular myocytes to lethal injury by high-intensity electrical fields

“…As a rule, it is considered that the likelihood of success of defibrillation keeps a positive relationship with shock strength, but only up to a certain point: increasing shock intensity above the optimal range diminishes success rate (Dosdall et al, 2010;Fotuhi et al, 1999). While poor underlying myocardial conditions may be partially accountable for the therapeutic failure of very strong shocks, HIEF itself may exert deleterious effects on the heart.…”

“…While poor underlying myocardial conditions may be partially accountable for the therapeutic failure of very strong shocks, HIEF itself may exert deleterious effects on the heart. Such effects include sustained membrane depolarization, cell damage and conduction block that may facilitate post-shock arrhythmia reinitiation (e.g., Dosdall et al, 2010;Fedorov et al, 2008;Fotuhi et al, 1999;Knisley and Grant, 1985;Oliveira et al, 2008;Sowell and Fast, 2012;Yabe et al, 1990).…”

Imaging the dynamics of individual electropores

“…Since its discovery and the first investigations in the 1960s and 1970s (4,5), electroporation has been used in a wide range of applications, including gene transfection (6), wound and water sterilization (7,8), tumor ablation (9,10), electrochemotherapy (11,12), and transdermal drug delivery (13). Furthermore, links to defibrillation damage have been highlighted (14).…”

Complex Structure and Dynamics of the Heart

“…However, several studies revealed that the expected depolarization patterns are not observed in real, well-connected tissue [91] and instead, additional heterogeneities in electrical conductance (including those on larger length scales) play a major role in the formation of these so-called secondary sources or virtual electrodes [92,93,94,95,96,97,98]. Electrical shocks above a critical defibrillation threshold of about 6 V/cm are believed to, on the one hand, activate a large enough tissue fraction by heterogeneity-induced virtual electrodes to terminate all existing waves and, on the other hand, minimize the risk of inducing new arrhythmias by interaction with preexisting activity [99,100]. However, as most of the studies are focused on elucidating the mechanisms of conventional, high-energy, defibrillation, they are lacking perspectives for the development of gentler defibrillation techniques.…”