Pulmonary vein isolation in treatment of atrial fibrillation using radiofrequency or cryoballoon ablation: factors associated with better clinical outcomes

Background: Electrical pulmonary vein isolation (PVI) is still regarded as a cornerstone for treatment of paroxysmal and persistent atrial fibrillation (AF). It can be achieved by different techniques. We investigated the indications and techniques of PVI using radiofrequency ablation (RFA) and cryoballoon ablation (CBA) for AF and compared the efficacy of the two techniques for persistent AF. Methods and results: First, we conducted a prospective, randomized (1:1), open-label, multi-centre clinical trial to evaluate the effectiveness of PVI performed with CBA in comparison with contact force-sensing RFA in patients with persistent AF. A total of 101 patients (52 in CBA and 49 in RFA) were enrolled and followed up for 12 months. The CBA group showed a similar clinical outcome to RFA in terms of freedom from atrial tachyarrhythmia at 12 months (69.2% in CBA vs. 61.2% in RFA, P=0.393). In addition, CBA showed comparable complications (1 in CBA vs. 4 in RFA, P=0.353), less atrial flutter (AFL) recurrence (3.9% in RFA vs. 18.0% in CBA, P=0.020), and shorter procedure and ablation time (158.9±28.9 vs. 197.9±38.4 minutes, 35.8±6.5 vs. 55.9±16.7 minutes, respectively, both P<0.001) than RFA. Second, we conducted an observational study in an RFA population, to investigate the impacts of procedural parameters on durability of PVI. We analysed the impacts of contact force (CF), power, and application time on ablation effect indicated by impedance drop (ID) in an RFA procedure with both conventional and high-power short-duration (HPSD) settings. We found that: (i) The minimum requirement of CF for effective ablation was 5 g. (ii) With CF ≥5 g, CF, power and application time can compensate for each other within restricted ranges, while the time to reach maximal ablation effect can be shortened by increasing CF or power output. (iii) The effect of HPSD ablation with 50 W for 10 s is equivalent to conventional ablation with 25 W for 40 s and 30-35 W for 20-30 s, in terms of ID. Changes of ID with increasing ablation index were similar at 30, 35 and 50 W. At 25 W they showed the same trend, but with smaller ID at the same ablation index. Third, we analysed the predictive value of procedural and biophysical parameters for the durability of PVI in a CBA population in a retrospective case-control study that used the data from 241 pulmonary veins of 71 patients who underwent a repeat AF ablation procedure. Thawing plateau time (TimeTP, defined as the time from 0 to 10℃ inside the balloon in the thawing period) was shown to be the strongest independent predictor for the durability of PVI. The relationship between TimeTP and the durability of PVI presents in a dose-proportional manner. TimeTP 25 s predicts durable PVI. In these two studies, we provided practical data for optimizing dose strategies for RFA and CBA to improve the durability of PVI. Finally, we performed a retrospective cohort study to investigate the incidence and risk factors for AF in 117 patients who suffered mostly AFL and underwent an elective cavotricuspid isthmus (CTI) ablation. During a mean follow-up period of 68 ± 24 months, 89 patients (70%) developed AF, 53 patients (42%) underwent AF ablation procedures, and 10 patients (8%) developed non-fatal ischemic cerebral events. Independent predictors for additional AF ablation included a higher CHA2DS2-vasc score (odds ratio (OR) 0.72, 95% confidence interval (CI), 0.53–0.98), documentation of both pre- and intraprocedural AF (OR 3.81, 95% CI, 1.14–12.8), and previous use of flecainide (OR 2.43, 95% CI, 1.06–5.58). We emphasized the high risk of AF occurrence and PVI in the future for AFL patients. The findings indicate that CTI block has limited prophylactic effect for AF episodes and that prophylactic PVI may be applied in selective AFL patients. Conclusions: (i) Compared with RFA, PVI performed by CBA offers shorter ablation time and procedure duration, with less AFL recurrence and similar freedom from atrial tachyarrhythmias at 12-month follow-up. (ii) Procedural parameters have predictive value and significant impacts on durability of PVI. (iii) Patients undergoing AFL ablation are at high risk of developing AF in the future and prophylactic PVI may be applied in selective AFL patients.Doktorgradsavhandlin

Equivalence of the equilibrium and the nonequilibrium molecular dynamics methods for thermal conductivity calculations: From bulk to nanowire silicon

Molecular dynamics simulations play an important role in studying heat transport in complex materials. The lattice thermal conductivity can be computed either using the Green-Kubo formula in equilibrium MD (EMD) simulations or using Fourier's law in nonequilibrium MD (NEMD) simulations. These two methods have not been systematically compared for materials with different dimensions and inconsistencies between them have been occasionally reported in the literature. Here we give an in-depth comparison of them in terms of heat transport in three allotropes of Si: three dimensional bulk silicon, two-dimensional silicene, and quasi-one-dimensional silicon nanowire. By multiplying the correlation time in the Green-Kubo formula with an appropriate effective group velocity, we can express the running thermal conductivity in the EMD method as a function of an effective length and directly compare it with the length-dependent thermal conductivity in the NEMD method. We find that the two methods quantitatively agree with each other for all the systems studied, firmly establishing their equivalence in computing thermal conductivity.Comment: 8 pages, 7 figure

Time-resolved Measurement of Quadrupole Wakefields in Corrugated Structures

Corrugated structures have recently been widely used for manipulating electron beam longitudinal phase space and for producing THz radiation. Here we report on time-resolved measurements of the quadrupole wakefields in planar corrugated structures. It is shown that while the time- dependent quadrupole wakefield produced by a planar corrugated structure causes significant growth in beam transverse emittance, it can be effectively canceled with a second corrugated structure with orthogonal orientation. The strengths of the time-dependent quadrupole wakefields for various corrugated structure gaps are also measured and found to be in good agreement with theories. Our work should forward the applications of corrugated structures in many accelerator based scientific facilities

Robust and Efficient Network Reconstruction in Complex System via Adaptive Signal Lasso

Network reconstruction is important to the understanding and control of collective dynamics in complex systems. Most real networks exhibit sparsely connected properties, and the connection parameter is a signal (0 or 1). Well-known shrinkage methods such as lasso or compressed sensing (CS) to recover structures of complex networks cannot suitably reveal such a property; therefore, the signal lasso method was proposed recently to solve the network reconstruction problem and was found to outperform lasso and CS methods. However, signal lasso suffers the problem that the estimated coefficients that fall between 0 and 1 cannot be successfully selected to the correct class. We propose a new method, adaptive signal lasso, to estimate the signal parameter and uncover the topology of complex networks with a small number of observations. The proposed method has three advantages: (1) It can effectively uncover the network topology with high accuracy and is capable of completely shrinking the signal parameter to either 0 or 1, which eliminates the unclassified portion in network reconstruction; (2) The method performs well in scenarios of both sparse and dense signals and is robust to noise contamination; (3) The method only needs to select one tuning parameter versus two in signal lasso, which greatly reduces the computational cost and is easy to apply. The theoretical properties of this method are studied, and numerical simulations from linear regression, evolutionary games, and Kuramoto models are explored. The method is illustrated with real-world examples from a human behavioral experiment and a world trade web.Comment: 15 pages, 8 figures, 4 table

Cryoballoon vs. radiofrequency catheter ablation: insights from NOrwegian randomized study of PERSistent Atrial Fibrillation (NO-PERSAF study)

Aims Pulmonary vein isolation (PVI) is still regarded as a cornerstone for treatment of persistent atrial fibrillation (AF). This study evaluated the effectiveness of PVI performed with cryoballoon ablation (CBA) in comparison with radiofrequency ablation (RFA) in patients with persistent AF. Methods and results  A total of 101 patients with symptomatic persistent AF were enrolled and randomized (1:1) to CBA or RFA groups and followed up for 12 months. The primary endpoint was any documented recurrent atrial tachyarrhythmia (ATA) lasting longer than 30 s following a 3-month blanking period. Secondary endpoints were procedure-related complications, procedure and ablation duration, and fluoroscopy time. The ATA-free survival curves were estimated by Kaplan–Meier method and analysed by the log-rank test. According to intention-to-treat analysis, freedom from ATA was achieved in 36 out of 52 patients in the CBA group and 30 out of 49 patients in the RFA group (69.2% vs. 61.2%, P = 0.393). No difference in AF recurrence was found between the two groups (27.5% in CBA vs. 38.0% in RFA, P = 0.258), and less atrial flutter recurrence was documented in the CBA group compared with the RFA group (3.9% vs. 18.0%, P = 0.020). The procedure and ablation duration were significantly shorter in the CBA group (160 ± 31 vs. 197 ± 38 min, P  0.05). Conclusion  Compared with RFA, PVI performed by CBA led to shorter procedure and ablation duration, with less atrial flutter recurrence and similar freedom from ATA at 12-month follow-up.publishedVersio

Thermal stability of Mg_2Si_(0.4)Sn_(0.6) in inert gases and atomic-layer-deposited Al_2O_3 thin film as a protective coating

Mg_2Si_(1−x)Sn_x solid solutions are promising thermoelectric materials to be applied in vehicle waste-heat recovery. Their thermal stability issue, however, needs to be addressed before the materials can be applied in practical thermoelectric devices. In this work, we studied the crystal structure and chemical composition of Mg_2Si_(1−x)Sn_x in inert gas atmosphere up to 823 K. We found that the sample was oxidized even in high-purity inert gases. Although no obvious structural change has been found in the slightly oxidized sample, carrier concentration decreased significantly since oxidation creates Mg vacancies in the lattice. We demonstrated that an atomic-layer deposited Al_2O_3 coating can effectively protect Mg_2Si_(1−x)Sn_x from oxidation in inert gases and even in air. In addition, this Al_2O_3 thin film also provides in situ protection to the Sb-doped Mg_2Si_(1−x)Sn_x samples during the laser-flash measurement and therefore eliminates the measurement error that occurs in uncoated samples as a result of sample oxidation and graphite exfoliation issues

Equivalence of the equilibrium and the nonequilibrium molecular dynamics methods for thermal conductivity calculations: From bulk to nanowire silicon

© 2018 American Physical Society. Molecular dynamics (MD) simulations play an important role in studying heat transport in complex materials. The lattice thermal conductivity can be computed either using the Green-Kubo formula in equilibrium MD (EMD) simulations or using Fourier's law in nonequilibrium MD (NEMD) simulations. These two methods have not been systematically compared for materials with different dimensions and inconsistencies between them have been occasionally reported in the literature. Here we give an in-depth comparison of them in terms of heat transport in three allotropes of Si: three-dimensional bulk silicon, two-dimensional silicene, and quasi-one-dimensional silicon nanowire. By multiplying the correlation time in the Green-Kubo formula with an appropriate effective group velocity, we can express the running thermal conductivity in the EMD method as a function of an effective length and directly compare it to the length-dependent thermal conductivity in the NEMD method. We find that the two methods quantitatively agree with each other for all the systems studied, firmly establishing their equivalence in computing thermal conductivity

Thawing plateau time indicating the duration of phase transition from ice to water is the strongest predictor for long-term durable pulmonary vein isolation after cryoballoon ablation for atrial fibrillation—Data from the index and repeat procedures

Introduction: This study aimed to clarify the relationship between the durability of pulmonary vein (PV) isolation and the time of phase transition from ice to water indicated by thawing plateau time in a cryoballoon ablation for atrial fibrillation (AF). Methods and results: In this retrospective study, 241 PVs from 71 patients who underwent a repeat AF ablation 526 (IQR: 412, 675) days after a cryoballoon ablation were analyzed. Reconnection was observed in 101 (41.9%) PVs of 53 patients (74.6%). Thawing plateau time (TimeTP) was defined as the time from 0°C to 10°C inside the balloon in the thawing period. Durable PV isolation was associated with significantly longer TimeTP compared with PV reconnection (26.0 vs. 11.0 s, P 25 s with a positive predictive value of 84.6% (sensitivity = 55.0%, specificity = 86.1%). In the analysis of multivariable logistic regression, location of PV reconnection (P < 0.01), TimeTP (P < 0.05) and thawing plateau integral (P < 0.01) were shown as independent predictors for durable PV isolation. Conclusion: TimeTP is an independent predictor for the durability of PV isolation, and it presents in a dose-proportional manner. TimeTP 25 s predicts durable PV isolation.publishedVersio

The impacts of contact force, power and application time on ablation effect indicated by serial measurements of impedance drop in both conventional and high-power short-duration ablation settings of atrial fibrillation

Background: This study aimed to clarify the interrelationship and additive effects of contact force (CF), power and application time in both conventional and high-power short-duration (HPSD) settings. Methods: Among 38 patients with paroxysmal atrial fibrillation who underwent first-time pulmonary vein isolation, 787 ablation points were collected at the beginning of the procedure at separate sites. Energy was applied for 60 s under power outputs of 25, 30 or 35 W (conventional group), or 10 s when using 50 W (HPSD group). An impedance drop (ID) of 10 Ω was regarded as a marker of adequate lesion formation. Results: ID ≥ 10 Ω could not be achieved with CF < 5 g under any power setting. With CF ≥ 5 g, ID could be enhanced by increasing power output or prolonging ablation time. ID for 30 and 35 W was greater than for 25 W (p < 0.05). Ablation with 35 W resulted in greater ID than with 30 W only when CF of 10–20 g was applied for 20–40 s (p < 0.05). Under the same power output, ID increased with CF level at different time points. The higher the CF, the shorter the time needed to reach ID of 10 Ω and maximal ID. ID correlated well with ablation index under each power, except for lower ID values at 25 W. ID with 50 W for 10 s was equivalent to that with 25 W for 40 s, but lower than that with 30 W for 40 s or 35 W for 30 s. Conclusions: CF of at least 5 g is required for adequate ablation effect. With CF ≥ 5g, CF, power output, and ablation time can compensate for each other. Time to reach maximal ablation effect can be shortened by increasing CF or power. The effect of HPSD ablation with 50 W for 10 s is equivalent to conventional ablation with 25 W for 40 s and 30–35 W for 20–30 s in terms of ID.publishedVersio