808 research outputs found
Short- and long-term experience in pulmonary vein segmental ostial ablation for paroxysmal atrial fibrillation*
Introduction: Segmental ostial pulmonary vein isolation (PVI) is considered a potentially curative therapeutic approach in the treatment of paroxysmal atrial fibrillation (PAF). There is only limited data available on the long-term effect of this procedure.
Methods: Patients (Pts) underwent a regular clinical follow up visit at 3, 6 and 24 months after PVI. Clinical success was classified as complete (i.e. no arrhythmia recurrences, no antiarrhythmic drug), partial (i.e. no/only few recurrences, on drug) or as a failure (no benefit). The clinical responder rate (CRR) was determined by combining complete and partial success.
Results: 117 patients (96 male, 21 female), aged 51±11 years (range 25 to 73) underwent a total of 166 procedures (1.4/patient) in 2-4 pulmonary veins (PV). 115 patients (98%) had AF, 2 patients presented with regular PV atrial tachycardia. ,109/115 patients. exhibited PAF as the primary arrhythmia (versus persistent AF). A total of 113 patients with PVI in the years 2001 to 2003 were evaluated for their CRR after 6 (3) months. A single intervention was carried out in 63 patients (55.8%), two interventions were performed in 45 patients (39.8%) and three interventions in 5 patients (4.4%). The clinical response demonstrated a complete success of 52% (59 patients), a partial success of 26% (29 patients) and a failure rate of 22% (25 patients), leading to a CRR of 78% (88 patients). Ostial PVI in all 4 PVs exhibited a tendency towards higher curative success rates (54% versus 44% in patients with 3 PVs ablated for the 6 month follow up). Long-term clinical outcome was evaluated in 39 patients with an ablation attempt at 3 PVs only (excluding the right inferior PV in our early experience) and a mean clinical follow up of 21±6 months. At this point in time the success rate was 41% (complete, 16 patients) and 21% (partial, 8 patients), respectively, adding up to a CRR of 62% (24 patients). In total, 20 patients (17.1%) had either a single or 2 (3 patients, 2.6%) complications independent of the number of procedures performed with PV stenosis as the leading cause (7.7%).
Conclusion: The CRR of patients with medical refractory PAF in our patient cohort is 78% at the 6 month follow up. PV stenosis is the main cause for procedure-related complications. Ablation of all 4 PV exhibits a tendency towards higher complete success rates despite equal CRR. Calculation of the clinical response after a mid- to long-term follow of 21±6 months in those patients with an ostial PVI in only 3 pulmonary veins (sparing the right inferior PV) shows a further reduction to 62%, exclusively caused by a drop in patients with a former partial success. To evaluate the long-term clinical benefit of segmental ostial PVI in comparison with other ablation techniques, more extended follow up periods are mandatory, including a larger study cohort and a detailed description of procedural parameters
Hanle Effect in Transport through Quantum Dots Coupled to Ferromagnetic Leads
We suggest a series of transport experiments on spin precession in quantum
dots coupled to one or two ferromagnetic leads. Dot spin states are created by
spin injection and analyzed via the linear conductance through the dot, while
an applied magnetic field gives rise to the Hanle effect. Such a Hanle
experiment can be used to determine the spin lifetime in the quantum dot, to
measure the spin injection efficiency into the dot, as well as proving the
existence of intrinsic spin precession which is driven by the Coulomb
interaction.Comment: 7 pages, 4 figures, minor changes, added reference
FMR and voltage induced transport in normal metal-ferromagnet-superconductor trilayers
We study the subgap spin and charge transport in normal
metal-ferromagnet-superconductor trilayers induced by bias voltage and/or
magnetization precession. Transport properties are discussed in terms of
time-dependent scattering theory. We assume the superconducting gap is small on
the energy scales set by the Fermi energy and the ferromagnetic exchange
splitting, and compute the non-equilibrium charge and spin current response to
first order in precession frequency, in the presence of a finite applied
voltage. We find that the voltage-induced instantaneous charge current and
longitudinal spin current are unaffected by the precessing magnetization, while
the pumped transverse spin current is determined by spin-dependent conductances
and details of the electron-hole scattering matrix. A simplified expression for
the transverse spin current is derived for structures where the ferromagnet is
longer than the transverse spin coherence length.Comment: 10 page
Kondo effect near the Van Hove singularity in biased bilayer graphene
Magnetic impurity adsorbed on one of the carbon planes of a bilayer graphene
is studied. The formation of the many-body SU(2) and SU(4) resonances close to
the bandgap is analyzed within the mean field Kotliar-Ruckenstein slave boson
approach. Impact of enhanced hybridization and magnetic instability of bilayer
doped near the Van Hove singularity on the screening of magnetic moment is
discussed.Comment: 10 pages, 8 figure
Electric-field controlled spin reversal in a quantum dot with ferromagnetic contacts
Manipulation of the spin-states of a quantum dot by purely electrical means
is a highly desirable property of fundamental importance for the development of
spintronic devices such as spin-filters, spin-transistors and single-spin
memory as well as for solid-state qubits. An electrically gated quantum dot in
the Coulomb blockade regime can be tuned to hold a single unpaired spin-1/2,
which is routinely spin-polarized by an applied magnetic field. Using
ferromagnetic electrodes, however, the properties of the quantum dot become
directly spin-dependent and it has been demonstrated that the ferromagnetic
electrodes induce a local exchange-field which polarizes the localized spin in
the absence of any external fields. Here we report on the experimental
realization of this tunneling-induced spin-splitting in a carbon nanotube
quantum dot coupled to ferromagnetic nickel-electrodes. We study the
intermediate coupling regime in which single-electron states remain well
defined, but with sufficiently good tunnel-contacts to give rise to a sizable
exchange-field. Since charge transport in this regime is dominated by the
Kondo-effect, we can utilize this sharp many-body resonance to read off the
local spin-polarization from the measured bias-spectroscopy. We show that the
exchange-field can be compensated by an external magnetic field, thus restoring
a zero-bias Kondo-resonance, and we demonstrate that the exchange-field itself,
and hence the local spin-polarization, can be tuned and reversed merely by
tuning the gate-voltage. This demonstrates a very direct electrical control
over the spin-state of a quantum dot which, in contrast to an applied magnetic
field, allows for rapid spin-reversal with a very localized addressing.Comment: 19 pages, 11 figure
Residual Kondo effect in quantum dot coupled to half-metallic ferromagnets
We study the Kondo effect in a quantum dot coupled to half-metallic
ferromagnetic electrodes in the regime of strong on-dot correlations. Using the
equation of motion technique for nonequilibrium Green functions in the slave
boson representation we show that the Kondo effect is not completely suppressed
for anti-parallel leads magnetization. In the parallel configuration there is
no Kondo effect but there is an effect associated with elastic cotunneling
which in turn leads to similar behavior of the local (on-dot) density of states
(LDOS) as the usual Kondo effect. Namely, the LDOS shows the temperature
dependent resonance at the Fermi energy which splits with the bias voltage and
the magnetic field. Moreover, unlike for non-magnetic or not fully polarized
ferromagnetic leads the only minority spin electrons can form such resonance in
the density of states. However, this resonance cannot be observed directly in
the transport measurements and we give some clues how to identify the effect in
such systems.Comment: 15 pages, 8 figures, accepted for publication in J. Phys.: Condens.
Mat
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