Low-voltage Defibrillation Research Articles

The impact of cardiac tissue anisotropy on spiral wave superseding: A simulation study using ionic cell models

Several types of dangerous cardiac arrhythmias, such as paroxysmal tachycardia and fibrillation, are linked with the spiral waves of electrical excitation in the heart muscle. In many cases, these diseases must be cured immediately after their diagnosis. Low-voltage defibrillation and cardioversion are modern treatment methods. Electrotherapy is based on spiral wave superseding by a high-frequency pacing from an electrode. In the present work, we study the influence of the anisotropic myocardial structure and cell-level model on cardioversion results. We use long line and point electrodes. Intervals of effective stimulation periods are determined and compared for two ionic cell-level models. Of all the considered factors, the cell-level model appears to play the greatest role in the results.

Success of spiral wave unpinning from heterogeneity in a cardiac tissue depends on its boundary conditions

The mechanism of the low voltage defibrillation is based on the drift of the spiral wave induced by a high frequency wave train. In the process, it is first necessary to unpin the wave from the stabilizing obstacle. We study the conditions of unpinning of a rotating wave anchored to the defect by posing the main accent on the boundary conditions of it. The computer simulations performed using the Korhonen model showed that the fluxes through the border of the defect in the cardiac tissue can significantly modify the excitation pattern, and the working frequency gap for the unpinning of reentry waves could be substantially reduced, making overdrive pacing procedure less effective or practically inapplicable.

Simulation of Overdrive Pacing in 2D Phenomenological Models of Anisotropic Myocardium

Spiral waves in the heart underlie dangerous cardiac arrhythmias such as fibrillation. Low-voltage defibrillation and cardioversion are modern methods to treat such pathologies. This type of electrotherapy is based on the phenomenon of superseding spiral waves by a high-frequency source of excitation. In this paper, we numerically simulated the superseding process in a thin layer of the cardiac muscle. We captured the case of a sole spiral wave with a stable core at the centre of a square. We used different cell-level models as well as a variety of electrode configurations and studied the induced drift of the spiral wave. Regimes of the external stimulation were classified based on whether they provide an effective and safe, that is without break-up, way to shift the spiral toward the boundary.

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

Low-voltage termination of ventricular tachycardia (VT) and atrial fibrillation has shown promising results; however, the mechanisms and full range of applications remain unexplored. To elucidate the mechanisms for low-voltage cardioversion and defibrillation and to develop an optimal low-voltage defibrillation protocol. 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). 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. 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.

Atrial defibrillation voltage: Falling to a new low

Atrial defibrillation voltage: Falling to a new low

Resonant drift of spiral waves in the complex ginzburg-landau equation.

Weak periodic external perturbations of an autowave medium can cause large-distance directed motion of the spiral wave. This happens when the period of the perturbation coincides with, or is close to the rotation period of a spiral wave, or its multiple. Such motion is called resonant or parametric drift. It may be used for low-voltage defibrillation of heart tissue. Theory of the resonant drift exists, but so far was used only qualitatively. In this paper, we show good quantitative agreement of the theory with direct numerical simulations. This is done for Complex Ginzburg-Landau Equation, one of the simplest autowave models.