Scroll waves in isotropic excitable media : linear instabilities, bifurcations and restabilized states

Scroll waves are three-dimensional analogs of spiral waves. The linear stability spectrum of untwisted and twisted scroll waves is computed for a two-variable reaction-diffusion model of an excitable medium. Different bands of modes are seen to be unstable in different regions of parameter space. The corresponding bifurcations and bifurcated states are characterized by performing direct numerical simulations. In addition, computations of the adjoint linear stability operator eigenmodes are also performed and serve to obtain a number of matrix elements characterizing the long-wavelength deformations of scroll waves.Comment: 30 pages 16 figures, submitted to Phys. Rev.

Monitoring intramyocardial reentry using alternating transillumination

Intramyocardial reentry is implicated as a primary cause of the most deadly cardiac arrhythmias known as polymorphic ventricular tachycardia and ventricular fibrillation. However, the mechanisms involved in the triggering of such reentry and controlling its subsequent dynamics remain poorly understood. One of the major obstacles has been a lack of adequate tools that would enable 3D imaging of electrical excitation and reentry inside thick ventricular wall. Here, we present a new experimental technique, termed alternating transillumination (AT), aimed at filling this gap. The AT technique utilizes a recently synthesized near-infrared fluorescent voltage-sensitive dye, DI-4-ANBDQBS. We apply AT to study the dynamics of reentry during shock-induced polymorphic ventricular tachycardia in pig myocardium

The use of embolic protection device in the stenting of brachiocephalic arteries

Objective — to optimize the results of endovascular treatment of stenotic pathology of brachiocephalic arteries. Materials and methods. The results of surgical treatment of 112 patients, among whom there were 79 (70.5 %) men and 33 (29.5 %) women aged from 28 to 86 years with symptomatic stenotic lesions of brachiocephalic arteries treated in the neurosurgical department of the Zaporizhzhia regional hospital in the period from 2010 to 2018 were analyzed. Observations were divided into three groups depending on the localization of the defeat: internal carotid artery — 74 (66 %) cases (predominant stenosis of the mouth of the ICA (n = 71)), vertebral artery — 25 (22.4 %), a portion of the subclavian artery or brachiocephalic trunk — 13 (11.6 %). All patients underwent MRI of the brain in the preoperative period, as well as in 45 (40 %) cases of CTangiography. In all cases prior to surgery invasive angiography was performed with an assessment of the state and anatomy of the brachiocephalic and intracranial arteries, as well as the possibilities of collateral blood flow. Results. In the first group, which was conducted carotid stenting embolic protection device was used in 72 (97.2 %) cases. In the second group, distal protection device were used twice 2 (8 %) in the resolution of extended stenoses of the dominant vertebral artery mouth. In the third group, the distal protection device was used in 1 (7.7 %) case for stenting the critical extended stenosis of the brachiocephalic trunk with the transition to common carotid artery. Complications were noted in 9 observations. In one case there was a development of ischemic stroke, intraoperatively, in a patient with an echeloned lesion of the intracranial basin of a stenting internal carotid artery, probably against a background of hypotension of the stent developed during implantation. In 8 (7.1 %) cases the formation of the hematoma of the puncture site of the femoral artery was noted. Conclusions. The use of embolic protection device is mandatory in standard carotid stenting. The choice of method of protection depends on the severity of stenosis, as well as the individual features of collateral blood flow. When stenting subclavian artery, brachiocephalic trunk and vertebral artery, in some cases it is justified to use distal protection devices, the latter increases the safety of the operation

A novel near-infrared voltage-sensitive dye reveals the action potential wavefront orientation at increased depths of cardiac tissue

Recently, novel near-infrared (NIR) voltage-sensitive dyes were developed for imaging electrical activity in blood-perfused hearts and for tomographic applications. However, their usefulness for conventional surface mapping is unclear. The spectral shift to the NIR range significantly increases the penetration depth of light into the tissue, thus increasing the intramural volume contributing to the optical action potential (OAP). Here, we characterize both computationally and experimentally the effect of increased penetration depth on the OAP upstroke, the OAP component most sensitive to optical scattering and absorption, and the activation maps. Optical imaging of cardiac electrical activity was performed in isolated rat hearts (n=5) paced from the LV mid free wall. We used the NIR dye JPW-6033 (excitation at 660nm, acquisition at >695nm). The conventional dye DI-4-ANEPPS (excitation at 532nm, acquisition at 700 DF50nm) was used for comparison. To simulate OAP we utilized a hybrid model that couples light transport equations with the model of electrical propagation. As expected, the switch from DI-4-ANEPPS to JPW-6033 significantly increased the upstroke duration: from 3.95±0.69ms to 5.39±0.82 ms, respectively. However, activation maps were largely unaffected. The correlation between the shape of the optical upstroke, and the averaged subsurface wave front orientation was also preserved. The computer simulations are in excellent agreement with the experimental data. In conclusion, our analysis suggests that despite significant increase in upstroke duration, the novel NIR dyes can be a useful alternative to conventional dyes in surface mapping applications

Far-field effect in bidomain model with a bath is defined by multiple space constants

Standing waves of depolarization, produced at the surface of rabbitheart in vitro by periodic voltage driving, eliminate propagationactivity in the heart, thus providing a defibrillating effect (Gray et.al., 2001). The phenomenon cannot be reproduced by cable orbidomain models of cardiac tissue. In such models, voltage appliedthrough an external electrode decays within the tissueexponentially with a space constant of ~1 mm.As a result, externalvoltage driving of such a tissue cannot generate standing waves,as only regions of the tissue near the electrode are entrained.However, a bidomain model of ventricular tissue, accounting forexistence of a bathing solution to which electrodes are applied,allows simulation of the standing waves in 1 and 2 dimensions(Aslanidi et. al., 2002).We consider a steady linear bidomain modelwith a bath, which describes steady distribution of voltage in apassive 1-dimensional tissue surrounded by a bathing solution.The model comprises three equations describing intracellularvoltage Vi, extracellular cleft voltage Ve, and voltage of the bath Vs

Vortex shedding as a precursor of turbulent electrical activity in cardiac muscle

In cardiac tissue, during partial blockade of the membrane sodium channels, or at high frequencies of excitation, inexcitable obstacles with sharp edges may destabilize the propagation of electrical excitation waves, causing the formation of self-sustained vortices and turbulent cardiac electrical activity. The formation of such vortices, which visually resembles vortex shedding in hydrodynamic turbulent flows, was observed in sheep epicardial tissue using voltage-sensitive dyes in combination with video-imaging techniques. Vortex shedding is a potential mechanism leading to the spontaneous initiation of uncontrolled high-frequency excitation of the heart

Lifetime enhancement of scroll rings by spatiotemporal fluctuations

The dynamics of three-dimensional scroll rings with spatiotemporal random excitability is investigated numerically using the FitzHugh-Nagumo model. Depending on the correlation time and length scales of the fluctuations, the lifetime of the ring filament is enlarged and a resonance effect between the time scale of the scroll ring and the time correlation of the noise is observed. Numerical results are interpreted in terms of a simplified stochastic model derived from the kinematical equations for three-dimensional excitable waves

Lifetime enhancement of scroll rings by spatiotemporal fluctuations

The dynamics of three-dimensional scroll rings with spatiotemporal random excitability is investigated numerically using the FitzHugh-Nagumo model. Depending on the correlation time and length scales of the fluctuations, the lifetime of the ring filament is enlarged and a resonance effect between the time scale of the scroll ring and the time correlation of the noise is observed. Numerical results are interpreted in terms of a simplified stochastic model derived from the kinematical equations for three-dimensional excitable waves