Atrial fibrillation (AF) is the most common cardiac arrhythmia and entails an increased risk of thromboembolic events. Prediction of the termination of an AF episode, based on noninvasive techniques, can benefit patients, doctors and health systems. The method described in this paper is based on two-lead surface electrocardiograms (ECGs): 1-min ECG recordings of AF episodes including N-type (not terminating within an hour after the end of the record), S-type (terminating 1 min after the end of the record) and T-type (terminating immediately after the end of the record). These records are organised into three learning sets (N, S and T) and two test sets (A and B). Starting from these ECGs, the atrial and ventricular activities were separated using beat classification and class averaged beat subtraction, followed by the evaluation of seven parameters representing atrial or ventricular activity. Stepwise discriminant analysis selected the set including dominant atrial frequency (DAF, index of atrial activity) and average HR (HRmean, index of ventricular activity) as optimal for discrimination between N/T-type episodes. The linear classifier, estimated on the 20 cases of the N and T learning sets, provided a performance of 90% on the 30 cases of a test set for the N/T-type discrimination. The same classifier led to correct classification in 89% of the 46 cases for N/S-type discrimination. The method has shown good results and seems to be suitable for clinical application, although a larger dataset would be very useful for improvement and validation of the algorithms and the development of an earlier predictor of paroxysmal AF spontaneous termination time.

In the context of HRV analysis, we evaluated the information content of two measures that can easily be derived from the classical RR time-domain indexes. The two measures are: 1) the ratio sd/rmssd, where sd is the RR standard deviation and rmssd is the root mean square of squared differences of consecutive RR beats; and 2) the ratio sd2/sd1, where sd2 and sd1 are extracted from the Poincaré plot and represent the transversal and longitudinal dispersion of the cloud of points (RR(i),RR(i)(+1)). We compared the performance of the two measures with that of the classical LF/HF ratio in a group of healthy subjects who underwent a 70 degrees upright tilt test. The goodness of the results obtained by the two measures, the simplicity of their calculation and their applicability free from a priori assumptions on the characteristics of the data are proposed to the attention of the community involved in the HRV analysis as a possible alternative to the LF/HF ratio.

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The PhysioNet Challenge 2004 addresses two differenr goals: to separate the persistent atrial $brillation (A F) from the paroxysmal AF (event I ) and, in case of paroxysmal AF, to identify the one-minute ECG strip just before the termination of the AF episode (event 2).Both events were approached through the separation of the atrial activity by the ventricular one in the ECG recordings (I-minute, two leads, 128 Hz). This separation was obtained through two different methods: a) QRST cancellation through cross-channel adaptive filtering; b) beat classification and class avernged beat subtraction.For event I , the averaged RR (index of ventricular uch'vity) was put into relationship with the Dominant Atrial Frequency (DAF) (index of atrial activity). A linear classifier was evaluated separating the RWDAF plane into the N-type and T-type regions. The best score was 95% on learning sets and 27/30 on testing set A.For event 2, once the S-type and T-type signals were joined for each patient using a QRST correlation method, sign9cative parameters were singled out in the DAFs during the penultimate and last two seconds of the S-rype and T-type recordings. Criteria based on rhe DAF trend of each signal in its last seconds and criteria based on the DAF comparison between S-rype and T-type signals were jointly used. The best score was 80% on learning sets and iBR0 on testing set B. IntroductionAtrial fibrillation (AF) is the most common arrhythmia. Paroxysmal (spontaneously terminated) atrial fibrillation (PAF) is, by evidence, antecedent to sustained AF that requires a pharmacological or external electrical intervention (cardioversion) to allow its termination. The risks of sustained AI3 are. nevertheless, serious because it predisposes to thromboembolism as a result of stasis and thrombus formation within the atria that can cause stroke or other thromboembolic events. Thus, the discrimination between paroxysmal and sustained AF and the prediction of PAF termination can be invaluable in order to avoid useless therapeutic interventions, to minimize the risks for the patient and to save money when the health care costs are strictly monitored.In normal conditions the atrial and the ventricular rhythms are coupled. Each heartbeat starts in the right atrium [l]. Here, the sinus node (SN), a natural pacemaker, sends an electrical signal. This signal spreads throughout the alria to the area between the atria and the ventricles called the atrioventricular (AV) node. The AV node connects to a group of special pathways that conduct the signal to the ventricles. Thus, first the a h a contract pumping blood into the ventricIes, and, a fraction of a second later, the ventricles contract sending blood throughout the body. In case of AF [Z], multiple wavefronts of depolarisation, termed wavelets, circulate more or less randomly across the atrial myocardium. The wavelets circle around, constantly changing area of conduction block, re-initiating themselves. In this case the P wave is substituted by a series of fibrillation waves (f waves)...

Lucus Planum, extending for a radius of approximately 500 km around 181°E, 5°S, is part of the Medusae Fossae Formation (MFF), a set of several discontinuous deposits of fine‐grained, friable material straddling across the Martian highland‐lowland boundary. The MFF has been variously hypothesized to consist of pyroclastic flows, pyroclastic airfall, paleopolar deposits, or atmospherically deposited icy dust driven by climate cycles. Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), a low‐frequency subsurface‐sounding radar carried by European Space Agency's Mars Express, acquired 238 radar swaths across Lucus Planum, providing sufficient coverage for the study of its internal structure and dielectric properties. Subsurface reflections were found only in three areas, marked by a distinctive surface morphology, while the central part of Lucus Planum appears to be made of radar‐attenuating material preventing the detection of basal echoes. The bulk dielectric properties of these areas were estimated and compared with those of volcanic rocks and ice‐dust mixtures. Previous interpretations that east Lucus Planum and the deposits on the northwestern flanks of Apollinaris Patera consist of high‐porosity pyroclastic material are strongly supported by the new results. The northwestern part of Lucus Planum is likely to be much less porous, although interpretations about the nature of the subsurface materials are not conclusive. The exact origin of the deposits cannot be constrained by radar data alone, but our results for east Lucus Planum are consistent with an overall pyroclastic origin, likely linked to Tharsis Hesperian and Amazonian activity.