Atrial defibrillation voltage: falling to a new low

Terminating ventricular tachyarrhythmias using far-field low-voltage stimuli: mechanisms and delivery protocols

BACKGROUND

Low-voltage termination of ventricular tachycardia (VT) and atrial fibrillation has shown promising results; however, the mechanisms and full range of applications remain unexplored.

OBJECTIVES

To elucidate the mechanisms for low-voltage cardioversion and defibrillation and to develop an optimal low-voltage defibrillation protocol.

METHODS

We developed a detailed magnetic resonance imaging-based computational model of the rabbit right ventricular wall. We applied multiple low-voltage far-field stimuli of various strengths (≤1 V/cm) and stimulation rates in VT and ventricular fibrillation (VF).

RESULTS

Of the 5 stimulation rates tested, stimuli applied at 16% or 88% of the VT cycle length (CL) were most effective in cardioverting VT, the mechanism being consecutive excitable gap decreases. Stimuli given at 88% of the VF CL defibrillated successfully, whereas a faster stimulation rate (16%) often failed because the fast stimuli did not capture enough tissue. In this model, defibrillation threshold energy for multiple low-voltage stimuli at 88% of VF CL was 0.58% of the defibrillation threshold energy for a single strong biphasic shock. Based on the simulation results, a novel 2-stage defibrillation protocol was proposed. The first stage converted VF into VT by applying low-voltage stimuli at times of maximal excitable gap, capturing large tissue volume and synchronizing depolarization; the second stage terminated VT. The energy required for successful defibrillation using this protocol was 57.42% of the energy for low-voltage defibrillation when stimulating at 88% of VF CL.

CONCLUSIONS

A novel 2-stage low-voltage defibrillation protocol using the excitable gap extent to time multiple stimuli defibrillated VF with the least energy by first converting VF into VT and then terminating VT.

Interdependent Relationship Between Atrial Fibrillation and Sinus Rhythm at the Hypothetical Interface of Atrial Fibrillation, Autonomic Tone, Sinoatrial Node and Inflammation : Analytical Review, Reconsiderations, Speculations and New Insights

Underlying mechanisms of atrial fibrillation occurrence and its self-extinguishing remain not completely investigated yet. The role of autonomic tone and sinoatrial node in the interplay between atrial fibrillation and sinus rhythm is also not fully understood. The influence of inflammation as a possible source of arrhythmia and likelihood of its pharmacologic treatment deserves special attention. These complex issues are important for better understanding of arrhythmogenesis and rhythm control. Conceptual reconsiderations through the new insights primarily on the hypothetic basis may delineate new therapeutic and preventive strategies. The aim of this analytical review was to reinforce the clinical and laboratory studies regarding the role of: 1) autonomic tone and sinoatrial node in restitution of sinus rhythm, 2) new concept of ?vibrantly quiescent stroboscopic tuning? as a matured status of atrial fibrillation being prepared for its abruption by slight impulse, 3) inflammation in the interplay between atrial fibrillation and sinus rhythm, 4) anti-inflammation and anti-allergic therapy to prevent and to treat the arrhythmia.

Modeling defibrillation of the heart: approaches and insights

Cardiac defibrillation, as accomplished nowadays by automatic, implantable devices (ICDs), constitutes the most important means of combating sudden cardiac death. While ICD therapy has proved to be efficient and reliable, defibrillation is a traumatic experience. Thus, research on defibrillation mechanisms, particularly aimed at lowering defibrillation voltage, remains an important topic. Advancing our understanding towards a full appreciation of the mechanisms by which a shock interacts with the heart is the most promising approach to achieve this goal. The aim of this paper is to assess the current state-of-the-art in ventricular defibrillation modeling, focusing on both numerical modeling approaches and major insights that have been obtained using defibrillation models, primarily those of realistic ventricular geometry. The paper showcases the contributions that modeling and simulation have made to our understanding of the defibrillation process. The review thus provides an example of biophysically based computational modeling of the heart (i.e., cardiac defibrillation) that has advanced the understanding of cardiac electrophysiological interaction at the organ level and has the potential to contribute to the betterment of the clinical practice of defibrillation.