Enhancing the optical excitation efficiency of a single self-assembled quantum dot with a plasmonic nanoantenna

We demonstrate how the controlled positioning of a plasmonic nanoparticle modifies the photoluminescence of a single epitaxial GaAs quantum dot. The antenna particle leads to an increase of the luminescence intensity by about a factor of eight. Spectrally and temporally resolved photoluminescence measurements prove an increase of the quantum dot's excitation rate. The combination of stable epitaxial quantum emitters and plasmonic nanostructures promises to be highly beneficial for nanoscience and quantum optics.Comment: 5 pages, 4 figure

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)

Short QT syndrome. Update on a recent entity

SummaryThe short QT syndrome, a recently discovered ion channel disorder, combines shortened repolarization, a predisposition to atrial and ventricular fibrillatory arrhythmias, and a risk of sudden death. Few cases have been reported, but the prevalence may be underestimated. This syndrome might account for some cases of unexplained ventricular fibrillation in patients with otherwise healthy hearts. Patients have abnormally short QT intervals and refractory periods, and atrial/ventricular fibrillation can be triggered during investigations. Gain-of-function mutations have been detected in three genes encoding potassium channels. Treatment is based on defibrillator implantation, sometimes as a preventive measure. Quinidine may be beneficial in certain cases

Is abnormal myocardial repolarization associated with the occurrence of malignant tachyarrhythmias in Takotsubo cardiomyopathy?

Background: Abnormalities of cardiac repolarization are a hallmark of Takotsubo cardiomyopathy (TC), but their association with the occurrence of syncope and ventricular tachyarrhythmias is unknown. This study sought to assess the relationship between myocardial repolarization and malignant tachyarrhythmias in TC.Methods: Clinical data and electrocardiographic repolarization parameters of 28 patients with TC and ventricular tachyarrhythmias (n = 26) or syncope (n = 2) were compared to data from 20 randomly selected patients with TC but without ventricular tachyarrhythmias or syncope.Results: Study patients had signifi cantly lower ejection fraction (EF) compared with controls (35 ± 14% vs. 46 ± 10%, p = 0.006). On day 1, no signifi cant differences in repolarization parameters were observed. However, in the subgroup with ventricular fi brillation ([VF]; n = 10), Tpeak-Tend in lead V6 was significantly prolonged (97 ± 20 vs. 85 ± 19 ms; p = 0.04). Similarly, in the subgroup with torsade de pointes ([TdP]; n = 5) Tpeak-Tend in lead V4 wasprolonged (127 ± 21 vs. 94 ± 27 ms; p = 0.001). On day 3, Tpeak-Tend in lead V3 (130 ± 51 vs. 105 ± 21 ms, p = 0.049) and Tpeak-Tend dispersion (56 ± 33 vs. 36 ± 21 ms; p = 0.03) were signifi cantly longer in study patients. The difference in Tpeak-Tend in lead V3 was borderline in the VF subgroup, but significant in the subgroup with TdP. The latter grouphad also longer Tpeak-Tend in lead V4 and longer corrected QT interval in leads V3 and V4.Conclusions: Patients with TC who experience malignant tachyarrhythmias have lower EF and a more pronounced alteration of the spatial dispersion of ventricular repolarization

Assessing Interaction Networks with Applications to Catastrophe Dynamics and Disaster Management

In this paper we present a versatile method for the investigation of interaction networks and show how to use it to assess effects of indirect interactions and feedback loops. The method allows to evaluate the impact of optimization measures or failures on the system. Here, we will apply it to the investigation of catastrophes, in particular to the temporal development of disasters (catastrophe dynamics). The mathematical methods are related to the master equation, which allows the application of well-known solution methods. We will also indicate connections of disaster management with excitable media and supply networks. This facilitates to study the effects of measures taken by the emergency management or the local operation units. With a fictious, but more or less realistic example of a spreading epidemic disease or a wave of influenza, we illustrate how this method can, in principle, provide decision support to the emergency management during such a disaster. Similar considerations may help to assess measures to fight the SARS epidemics, although immunization is presently not possible

CMR findings in patients with hypertrophic cardiomyopathy and atrial fibrillation

<p>Abstract</p> <p>Objectives</p> <p>We sought to evaluate the relation between atrial fibrillation (AF) and the extent of myocardial scarring together with left ventricular (LV) and atrial parameters assessed by late gadolinium-enhancement (LGE) cardiovascular magnetic resonance (CMR) in patients with hypertrophic cardiomyopathy (HCM).</p> <p>Background</p> <p>AF is the most common arrhythmia in HCM. Myocardial scarring is also identified frequently in HCM. However, the impact of myocardial scarring assessed by LGE CMR on the presence of AF has not been evaluated yet.</p> <p>Methods</p> <p>87 HCM patients underwent LGE CMR, echocardiography and regular ECG recordings. LV function, volumes, myocardial thickness, left atrial (LA) volume and the extent of LGE, were assessed using CMR and correlated to AF. Additionally, the presence of diastolic dysfunction and mitral regurgitation were obtained by echocardiography and also correlated to AF.</p> <p>Results</p> <p>Episodes of AF were documented in 37 patients (42%). Indexed LV volumes and mass were comparable between HCM patients with and without AF. However, indexed LA volume was significantly higher in HCM patients with AF than in HCM patients without AF (68 ± 24 ml·m^-2versus 46 ± 18 ml·m^-2, p = 0.0002, respectively). The mean extent of LGE was higher in HCM patients with AF than those without AF (12.4 ± 14.5% versus 6.0 ± 8.6%, p = 0.02). When adjusting for age, gender and LV mass, LGE and indexed LA volume significantly correlated to AF (r = 0.34, p = 0.02 and r = 0.42, p < 0.001 respectively). By echocardiographic examination, LV diastolic dysfunction was evident in 35 (40%) patients. Mitral regurgitation greater than II was observed in 12 patients (14%). Multivariate analysis demonstrated that LA volume and presence of diastolic dysfunction were the only independent determinant of AF in HCM patients (p = 0.006, p = 0.01 respectively). Receiver operating characteristic curve analysis indicated good predictive performance of LA volume and LGE (AUC = 0.74 and 0.64 respectively) with respect to AF.</p> <p>Conclusion</p> <p>HCM patients with AF display significantly more LGE than HCM patients without AF. However, the extent of LGE is inferior to the LA size for predicting AF prevalence. LA dilation is the strongest determinant of AF in HCM patients, and is related to the extent of LGE in the LV, irrespective of LV mass.</p