32 research outputs found
Left Atrial Chamber and Appendage Function After Internal Atrial Defibrillation: A Prospective and Serial Transesophageal Echocardiographic Study
AbstractObjectives. The purpose of this prospective study was to assess left atrial chamber and appendage function after internal atrial defibrillation of atrial fibrillation and to evaluate the time course of recovery.Background. External cardioversion of atrial fibrillation may result in left atrial appendage dysfunction (“stunning”) and may promote thrombus formation. In contrast to external cardioversion, internal atrial defibrillation utilizes lower energies; however, it is unknown whether the use of lower energies may avoid stunning of the left atrial appendage.Methods. Transesophageal and transthoracic echocardiography were performed in 20 patients 24 h before and 1 and 7 days after internal atrial defibrillation to assess both left atrial chamber and appendage function. Transthoracic echocardiography was again performed 28 days after internal atrial defibrillation to assess left atrial function. The incidence and degree of spontaneous echo contrast accumulation (range 1+ to 4+) was noted, and peak emptying velocities of the left atrial appendage were measured before and after internal atrial defibrillation. To determine left atrial mechanical function, peak A wave velocities were obtained from transmitral flow velocity profiles.Results. Sinus rhythm was restored in all patients. The mean ± SD peak A wave velocities increased gradually after cardioversion, from 0.47 ± 0.16 m/s at 24 h to 0.61 ± 0.13 m/s after 7 days (p < 0.05) and 0.63 ± 0.13 m/s after 4 weeks. Peak emptying velocities of the left atrial appendage were 0.37 ± 0.16 m/s before internal atrial defibrillation, decreased significantly after internal atrial defibrillation to 0.23 ± 0.1 m/s at 24 h (p < 0.01) and then recovered to 0.49 ± 0.23 m/s (p < 0.01) after 7 days. The corresponding values for the degree of spontaneous echo contrast were 1.2 ± 1.2 before internal atrial defibrillation versus 2.0 ± 1.0 (p < 0.01) and 1.1 ± 1.3 (p < 0.01) 1 and 7 days after cardioversion, respectively. One patient developed a new thrombus in the left atrial appendage, and another had a thromboembolic event after internal atrial defibrillation.Conclusions. Internal atrial defibrillation causes depressed left atrial chamber and appendage function and may result in the subacute accumulation of spontaneous echo contrast and development of new thrombi after cardioversion. These findings have important clinical implications for anticoagulation therapy before and after low energy internal atrial defibrillation in patients with atrial fibrillation.(J Am Coll Cardiol 1997;29:131–8)
Characterization of Mott-insulating and superfluid phases in the one-dimensional Bose--Hubbard model
We use strong-coupling perturbation theory, the variational cluster approach
(VCA), and the dynamical density-matrix renormalization group (DDMRG) method to
investigate static and dynamical properties of the one-dimensional
Bose--Hubbard model in both the Mott-insulating and superfluid phases. From the
von Neumann entanglement entropy we determine the central charge and the
transition points for the first two Mott lobes. Our DMRG results for the
ground-state energy, momentum distribution function, boson correlation function
decay, Mott gap, and single particle-spectral function are reproduced very well
by the strong-coupling expansion to fifth order, and by VCA with clusters up to
12 sites as long as the ratio between the hopping amplitude and on-site
repulsion, t/U, is smaller than 0.15 and 0.25, respectively. In addition, in
the superfluid phase VCA captures well the ground-state energy and the sound
velocity of the linear phonon modes. This comparison provides an authoritative
estimate for the range of applicability of these methods. In strong-coupling
theory for the Mott phase, the dynamical structure factor is obtained from the
solution of an effective single-particle problem with an attractive potential.
The resulting resonances show up as double-peak structure close to the
Brillouin zone boundary. These high-energy features also appear in the
superfluid phase which is characterized by a pronounced phonon mode at small
momenta and energies, as predicted by Bogoliubov and field theory. In one
dimension, there are no traces of an amplitude mode in the dynamical
single-particle and two-particle correlation functions.Comment: 15 pages, 12 figure
Quantum Monte Carlo and variational approaches to the Holstein model
Based on the canonical Lang-Firsov transformation of the Hamiltonian we
develop a very efficient quantum Monte Carlo algorithm for the Holstein model
with one electron. Separation of the fermionic degrees of freedom by a
reweighting of the probability distribution leads to a dramatic reduction in
computational effort. A principal component representation of the phonon
degrees of freedom allows to sample completely uncorrelated phonon
configurations. The combination of these elements enables us to perform
efficient simulations for a wide range of temperature, phonon frequency and
electron-phonon coupling on clusters large enough to avoid finite-size effects.
The algorithm is tested in one dimension and the data are compared with
exact-diagonalization results and with existing work. Moreover, the ideas
presented here can also be applied to the many-electron case. In the
one-electron case considered here, the physics of the Holstein model can be
described by a simple variational approach.Comment: 18 pages, 11 Figures, v2: one typo correcte
950-94 Real-time Three-dimensional Intracoronary Ultrasonography: High Resolution Dynamic Images of Coronary Artery Lesions
Intravascular ultrasound displays coronary arteries in independent crosssectional images with no axial information. Three-dimensional reconstruction is mandatory, but cardiac cycle linked vessel motions and torsions of the arteries do not allow to apply simple devices that are used for peripheral vessels.Methods and results:We used a 2.9 F 30 MHz intravascular imaging system in combination with a motorized catheter pullback device. ECG and respiration triggering was performed and cubic datasets were acquired with a time resolution of 25 frames/s. Axial increments were set at 0.1 mm over a distance along the vessels of 25 to 35 mm. After processing the original registrations, three-dimensional real-time images could be created in any plane through the dataset. 25 patients with coronary artery disease were investigated before and after therapeutic interventions including Palmaz-Schatz stents (n=6), laser angioplasty (n=5), directional atherectomy (n=41, and balloon angioplasty (n=21). The system provided excellent images in all patients. Since the spatial geometry of the stents was known the reliability of the three-dimensional images could easily be proven. Dissection membranes, plaques and vessel takeoffs were clearly visualized in their spatial orientation, and the effect of interventions could be demonstrated in all cases. Major problems arise from tortuous vessels with regionally reduced original image quality and from surface definitions by user dependent settings of the noiselthreshold level.ConclusionReal-time three-dimensional reconstruction of the coronary arteries is possible and extends future application of intravascular sonography