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Search Results: 1 - 10 of 198119 matches for " Tchavdar N. Shalganov "
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Inadvertent isolation of a focal tachycardia within the superior vena cava  [PDF]
Milko K. Stoyanov, Tchavdar N. Shalganov
World Journal of Cardiovascular Diseases (WJCD) , 2012, DOI: 10.4236/wjcd.2012.24050
Abstract: The superior vena cava (SVC) is known to be a potential source of focal atrial tachycardias. Not uncommonly these tachycardias trigger atrial fibrillation or flutter. Focal ablation is safe and effective in eliminating arrhythmogenic foci within the SVC. We present the case of a patient with focal atrial tachycardia arising from the SVC. During presumably focal ablation inadvertent electrical isolation of the SVC from the right atrium was achieved, with restoration of sinus rhythm in the atria and persistence of the tachycardia within the SVC.
Incisional Atrial Tachycardia Masquerading As Counter-clockwise Atrial Flutter
Tchavdar N Shalganov,Mihail M Protich
Indian Pacing and Electrophysiology Journal , 2010,
Abstract: Forty-four-year-old male patient with surgical closure of ostium secundum type atrial septal defect at the age of 9 years had undergone radiofrequency catheter ablation of the cavotricuspid isthmus because of recurrent drug-resistant typical isthmus-dependent atrial flutter, with bi-directional isthmus block achieved. Only few days later he started to suffer again high-rate tachycardia. An atypical atrial flutter was diagnosed on ECG (Figure 1). This one proved to be drug-resistant as well and recurred promptly after cardioversion.
Preventing complicated transseptal puncture with intracardiac echocardiography: case report
Tchavdar Shalganov, Dora Paprika, Sarolta Borbás, András Temesvári, Tamás Szili-T?r?k
Cardiovascular Ultrasound , 2005, DOI: 10.1186/1476-7120-3-5
Abstract: A case of a patient with paroxysmal atrial fibrillation and atrial flutter, and distorted intracardiac anatomy is presented. Intracardiac echocardiography showed a small oval fossa abouting to an enlarged aorta anteriorly. A very small distance from the interatrial septum to the left atrial free wall was seen. The latter two conditions were predisposing to a complicated transseptal puncture. According to fluoroscopy the transseptal needle had a correct position, but the intracardiac echo image showed that it was actually pointing towards the aortic root and most importantly, that it was virtually impossible to stabilize it in the fossa itself. Based on intracardiac echo findings a decision was made to limit the procedure only to ablation of the cavotricuspid isthmus and not to proceed further so as to avoid complications.This case report illustrates the usefulness of the intracardiac echocardiography in preventing serious or even fatal complications in transseptal procedures when the cardiac anatomy is unusual or distorted. It also helps to understand the possible mechanisms of mechanical complications in cases where fluoroscopic images are apparently normal.Since the advent of ICE in the electrophysiology practice it proved its value in guiding transseptal procedures with providing an extra safety margin for the patients. The possibility to visualize the oval fossa, the LA free wall and the aortic root helps in preventing mechanical complications. ICE can visualize also intracardiac thrombus and spontaneous echocontrast, which is helpful in avoiding thromboembolic complications. Although the value of ICE is well known, it is rather hard to admit that it is a universal tool for achieving uncomplicated access to the left atrium. The aim of this case presentation is to show that ICE can lead to interruption of a transseptal procedure due to the presence of risk factors for mechanical complications when the fluoroscopic image is seemingly satisfying.A seventy-year-old
Mid-term echocardiographic follow up of left ventricular function with permanent right ventricular pacing in pediatric patients with and without structural heart disease
Tchavdar Shalganov, Dora Paprika, Radu Vatasescu, Attila Kardos, Attila Mihalcz, Laszlo Kornyei, Andras Szatmari, Tamas Szili-Torok
Cardiovascular Ultrasound , 2007, DOI: 10.1186/1476-7120-5-13
Abstract: A group of 99 pediatric patients with previously implanted pacemaker was studied retrospectively. Forty-three patients (21 males) had isolated congenital complete or advanced atrioventricular block. The remaining 56 patients (34 males) had pacing indication in the presence of structural heart disease. Thirty-two of them (21 males) had isolated structural heart disease and the remaining 24 (13 males) had complex congenital heart disease. Patients were followed up for an average of 53 ± 41.4 months with 12-lead electrocardiogram and transthoracic echocardiography. Left ventricular shortening fraction was used as a marker of ventricular function. QRS duration was assessed using leads V5 or II on standard 12-lead electrocardiogram.Left ventricular shortening fraction did not change significantly after pacemaker implantation compared to preimplant values overall and in subgroups. In patients with complex congenital heart malformations shortening fraction decreased significantly during the follow up period. (0.45 ± 0.07 vs 0.35 ± 0.06, p = 0.015). The correlation between the change in left ventricular shortening fraction and the mean increase of paced QRS duration was not significant. Six patients developed dilated cardiomyopathy, which was diagnosed 2 months to 9 years after pacemaker implantation.Chronic right ventricular pacing in pediatric patients with or without structural heart disease does not necessarily result in decline of left ventricular function. In patients with complex congenital heart malformations left ventricular shortening fraction shows significant decrease.Chronic right ventricular (RV) apical pacing alters unfavorably left ventricular (LV) electrical activation, mechanical contraction, cardiac output, myocardial perfusion and histology. Permanent RV pacing may have detrimental effect on LV function and may promote to heart failure in adult patients with LV dysfunction [1-10]. The effect of chronic RV apical pacing on LV performance in pediatric pati
On the Newtonian origin of the spin motive force in ferromagnetic atomic wires
Maria Stamenova,Tchavdar N. Todorov,Stefano Sanvito
Physics , 2007, DOI: 10.1103/PhysRevB.77.054439
Abstract: We demonstrate numerically the existence of a spin-motive force acting on spin-carriers when moving in a time and space dependent internal field. This is the case of electrons in a one-dimensional wires with a precessing domain wall. The effect can be explained solely by considering adiabatic dynamics and it is shown to exist for both classical and quantum systems.
Current-driven magnetic rearrangements in spin-polarized point contacts
Maria Stamenova,Stefano Sanvito,Tchavdar N. Todorov
Physics , 2005, DOI: 10.1103/PhysRevB.72.134407
Abstract: A new method for investigating the dynamics of atomic magnetic moments in current-carrying magnetic point contacts under bias is presented. This combines the non-equilibrium Green's function (NEGF) method for evaluating the current and the charge density with a description of the dynamics of the magnetization in terms of quasistatic thermally-activated transitions between stationary configurations. This method is then implemented in a tight-binding (TB) model with parameters chosen to simulate the main features of the electronic structures of magnetic transition metals. We investigate the domain wall (DW) migration in magnetic monoatomic chains sandwiched between magnetic leads, and for realistic parameters find that collinear arrangement of the magnetic moments of the chain is always favorable. Several stationary magnetic configurations are identified, corresponding to a different number of Bloch walls in the chain and to a different current. The relative stability of these configurations depends on the geometrical details of the junction and on the bias, however we predict transitions between different configurations with activation barriers of the order of a few tens of meV. Since different magnetic configurations are associated to different resistances, this suggests an intrinsic random telegraph noise at microwave frequencies in the I-V characteristics of magnetic atomic point contacts at room temperature. Finally, we investigate whether or not current induced torques are conservative.
Length matters: keeping atomic wires in check
Brian Cunningham,Tchavdar N. Todorov,Daniel Dundas
Physics , 2015, DOI: 10.1557/opl.2015.197
Abstract: Dynamical effects of non-conservative forces in long, defect free atomic wires are investigated. Current flow through these wires is simulated and we find that during the initial transient, the kinetic energies of the ions are contained in a small number of phonon modes, closely clustered in frequency. These phonon modes correspond to the waterwheel modes determined from preliminary static calculations. The static calculations allow one to predict the appearance of non-conservative effects in advance of the more expensive real-time simulations. The ion kinetic energy redistributes across the band as non-conservative forces reach a steady state with electronic frictional forces. The typical ion kinetic energy is found to decrease with system length, increase with atomic mass, and its dependence on bias, mass and length is supported with a pen and paper model. This paper highlights the importance of non-conservative forces in current carrying devices and provides criteria for the design of stable atomic wires.
Nonconservative dynamics in long atomic wires
Brian Cunningham,Tchavdar N. Todorov,Daniel Dundas
Physics , 2014, DOI: 10.1103/PhysRevB.90.115430
Abstract: The effect of nonconservative current-induced forces on the ions in a defect-free metallic nanowire is investigated using both steady-state calculations and dynamical simulations. Non-conservative forces were found to have a major influence on the ion dynamics in these systems, but their role in increasing the kinetic energy of the ions decreases with increasing system length. The results illustrate the importance of nonconservative effects in short nanowires and the scaling of these effects with system size. The dependence on bias and ion mass can be understood with the help of a simple pen and paper model. This material highlights the benefit of simple preliminary steady-state calculations in anticipating aspects of brute-force dynamical simulations, and provides rule of thumb criteria for the design of stable quantum wires.
Non-conservative current-driven dynamics: beyond the nanoscale
Brian Cunningham,Tchavdar N. Todorov,Daniel Dundas
Physics , 2015,
Abstract: Long metallic nanowires combine crucial factors for non-conservative current-driven atomic mo- tion. These systems have degenerate vibrational frequencies, clustered about a Kohn anomaly in the dispersion relation, that can couple under current to form non-equilibrium modes of motion growing exponentially in time. Such motion is made possible by non-conservative current-induced forces on atoms, and we refer to it generically as the waterwheel effect. Here the connection be- tween the waterwheel effect and the stimulated directional emission of phonons propagating along the electron flow is discussed in an intuitive manner. Non-adiabatic molecular dynamics show that waterwheel modes self-regulate by reducing the current and by populating modes nearby in fre- quency, leading to a dynamical steady state in which non-conservative forces are counter-balanced by the electronic friction. The waterwheel effect can be described by an appropriate effective non- equilibrium dynamical response matrix. We show that the current-induced parts of this matrix in metallic systems are long-ranged, especially at low bias. This non-locality is essential for the characterisation of non-conservative atomic dynamics under current beyond the nanoscale.
On the density-potential mapping in time-dependent density functional theory
Neepa T. Maitra,Tchavdar N. Todorov,Chris Woodward,Kieron Burke
Physics , 2009, DOI: 10.1103/PhysRevA.81.042525
Abstract: The key questions of uniqueness and existence in time-dependent density functional theory are usually formulated only for potentials and densities that are analytic in time. Simple examples, standard in quantum mechanics, lead however to non-analyticities. We reformulate these questions in terms of a non-linear Schr\"odinger equation with a potential that depends non-locally on the wavefunction.
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