Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators

Whispering gallery resonators (WGR's), based on total internal reflection, possess high quality factors in a broad spectral range. Thus, nonlinear optical processes in such cavities are ideally suited for the generation of broadband or tunable electromagnetic radiation. Experimentally and theoretically, we investigate the tunability of optical parametric oscillation in a radially structured WGR made of lithium niobate. With a 1.04 /mum pump wave, the signal and idler waves are tuned from 1.78 to 2.5 \mum - including the point of degeneracy - by varying the temperature between 20 and 62 {\deg}C. A weak off-centering of the radial domain structure extends considerably the tuning capabilities. The oscillation threshold lies in the mW-power range.Comment: 4 pages, 5 figure

Continuous localization of cardiac activation sites using a database of multichannel ECG recordings

Monomorphic ventricular tachycardia and ventricular extrasystoles have a specific exit site that can be localized using the multichannel surface electrocardiogram (ECG) and a database of paced ECG recordings. An algorithm is presented that improves on previous methods by providing a continuous estimate of the coordinates of the exit site instead of selecting one out of 25 predetermined segments. The accuracy improvement is greatest, and most useful, when adjacent pacing sites in individual patients are localized relative to each other. Important advantages of the new method are the objectivity and reproducibility of the localization result

Request-TDMA: A multiple-access protocol for wireless multimedia networks

This paper describes a cellular multiple-access scheme based on TDMA for multimedia communication networks. The scheme proposes an admission control of two different multimedia application stream types: real-time and non-real-time. We do not consider interference between cells. The proposed protocol, that is based on TDMA, exploits the available bandwidth fully. The throughput per mobile station is higher compared to other multiple-access protocols, it offers low latency for both real-time and nonreal-time communication and the unused reserved bandwidth is reallocated for non-real-time communication. Furthermore, the throughput and latency remain stable under high loads

Relatie tussen farmacokinetiek van ajmaline en ST-elevatie bij de diagnostiek van het Brugada-syndroom

Association between pharmacokinetics of ajmaline and ST elevation in diagnostics of Brugada syndrome OBJECTIVE To investigate the relationship between ajmaline serum levels (pharmacokinetics, PK] and changes in the ST segment on the electrocardiogram (pharmacodynamics, PD] in patients with suspected Brugada syndrome (BS). DESIGN AND METHODS We determined the PK profile of ajmaline in 34 patients referred to the cardiology clinic for diagnosis of Brugada syndrome. The PD profile was derived from the ST elevations on the electrocardiograms of 26 patients during the diagnostics of BS. The PK and PD data were examined and fitted into non-linear mixed effect modelling (NONMEM 7). The final PK model was evaluated with data from 8 newly included patients. RESULTS Pharmacokinetics of ajmaline was best described with a two compartment model and the PK/PD data as a direct effect with a linear relationship between ajmaline serum levels and ST segment elevation. In BS-positive patients the baseline ST segment was 0.06 mV (rsd 35%] with a slope of 0.03 mV·mL/μg (rsd 94%). In BS-negative patients no association was found between ajmaline serum levels and ST segment elevation. CONCLUSION Pharmacokinetics of ajmaline in patients with suspected BS is best described with a two compartment model with linear elimination. A direct association between ajmaline serum levels and ST segment elevation in BS-positive patients was found. No association was found between ajmaline serum levels and ST segment elevation in BS-negative patients. In future studies this model can be used to examine the effects of co-variates in order to optimize the use of ajmaline in the diagnosis of BS

Mapping and Surgical Ablation of Focal Epicardial Left Ventricular Tachycardia

We describe a technical challenge in a 17-year-old patient with incessant epicardial focal ventricular arrhythmia and diminished LV function. Failure of ablation at the earliest activated endocardial site during ectopy suggested an epicardial origin, which was supported by specific electrocardiographic criteria. Epicardial ablation was not possible due to the localization of the origin of the ventricular tachycardia adjacent to the phrenic nerve. Minimal invasive surgical multielectrode high-density epicardial mapping was performed to localize the arrhythmia focus. Epicardial surgical RF ablation resulted in the termination of ventricular ectopy. After 2 years, the patient is still free from arrhythmias

Body surface mapping during pacing at multiple sites in the human atrium: P-wave morphology of ectopic right atrial activation

The morphology and polarity of the P wave on 12-lead ECG are of limited clinical value in localizing ectopic atrial rhythms. It was the aim of this study to assess the spatial resolution of body surface P-wave integral mapping in identifying the site of origin of ectopic right atrial (RA) impulse formation in patients without structural atrial disease. Sixty-two-lead ECG recordings were obtained during RA pacing at 86 distinct endocardial sites in nine patients with normal biatrial anatomy. After P-wave integral maps were generated for each paced activation sequence, 17 groups with nearly identical map features were visually selected, and a mean P-wave integral map was computed for each group. Supportive statistical analysis to corroborate qualitative group selection was performed by assessment of (1) intragroup pattern uniformity by use of jackknife correlation coefficient analysis of the integral maps contained in each group and (2) intergroup pattern variability by use of the calculation of cross correlations between the 17 mean integral maps. The spatial resolution of paced P-wave body surface mapping in the right atrium was obtained by estimating the area size of endocardial segments with nearly identical P-wave integral maps by use of a biplane fluoroscopic method to compute the three-dimensional position of each pacing site. The latter approach yielded a mean endocardial segment size of 3.5+/-2.9 cm2 (range, 0.79 to 10.75 cm2). Use of the P-wave morphology on the 62-lead surface ECG in patients with normal biatrial anatomy allows separation of the origin of ectopic RA impulse formation into one of 17 different endocardial segments with an approximated area size of 3.5 cm2. This database of paced P-wave integral maps provides a versatile clinical tool to perform detailed noninvasive localization of right-sided atrial tachycardia before radiofrequency catheter ablatio

Activation delay after premature stimulation in chronically diseased human myocardium relates to the architecture of interstitial fibrosis

BACKGROUND: Progressive activation delay starting at long coupling intervals of premature stimuli has been shown to correlate with sudden cardiac death in patients with hypertrophic cardiomyopathy. The purpose of this study was to elucidate the mechanism of increased activation delay in chronically diseased myocardium. METHODS AND RESULTS: High-resolution unipolar mapping (105, 208, or 247 recording sites with interelectrode distances of 0.8, 0.5, or 0.3 mm, respectively) of epicardial electrical activity was carried out during premature stimulation in 11 explanted human hearts. The hearts came from patients who underwent heart transplantation and were in the end stage of heart failure (coronary artery disease, 4; hypertrophic cardiomyopathy, 1; and dilated cardiomyopathy, 6). Eight hearts were Langendorff-perfused. Epicardial sheets were taken from the remaining hearts and studied in a tissue bath. Activation maps and conduction curves were constructed and correlated with histology. Conduction curves revealing prominent increase of activation delay were associated with zones of dense, patchy fibrosis with long fibrotic strands. Dense, diffuse fibrosis with short fibrotic strands only marginally affected conduction curves. The course of conduction curves in patchy fibrotic areas greatly depended on the direction of propagation relative to fiber direction. CONCLUSIONS: The study demonstrates that in chronically diseased human myocardium, nonuniform anisotropic characteristics imposed by long fibrotic strands cause a progressive increase of activation delay, starting at long coupling intervals of premature stimuli. The increase strongly depends on the direction of the wave front with respect to fiber direction and the architecture of fibrosi