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An improved high-solid-loading slurry impregnation process was developed to introduce HfB2 particles into a low-density C/C preform efficiently, and precursor infiltration and pyrolysis process was used for densification to obtain a C/C-HfB2-SiC composite. The microstructure characterization revealed that HfB2 particles uniformly filled the pores in the C/C preform, and SiC well densified the interstices between HfB2 particles and the small pores in the carbon fiber bundles. After being tested, the C/C-HfB2-SiC composite had a density of 4.07 g/cm3 and a bending strength of 344.8 MPa, and exhibited a non-brittle fracture behavior. After ablation with oxyacetylene flame at 2500 ℃ for 120 s, the mass ablation rate and linear ablation rate of the C/C-HfB2-SiC composite were 0.5 mg/s and 0.415 μm/s, respectively. The good ablation performance is attributed to the hindering effect of the HfO2 scale on oxygen diffusion at high temperature.

The ablation properties and mechanisms of BN-coated Cf-reinforced SiBCNZr composites under an oxyacetylene combustion torch were investigated. The mass and linear ablation rates of the Cf/SiBCNZr ceramic matrix composites were lower than those of Cf/SiBCN and SiCf/SiBCN composites, reaching 0.0022 mg/s and 0.0136 mm/s, respectively. The ablation resistance of the SiBCN ceramics was enhanced by the addition of Zr, whereas the BN-coated Cf increased the thermal shock resistance of the SiBCNZr ceramics. No macrocracks were found on the ablation surface of the Cf/SiBCNZr specimen. The ablation mechanisms based on different ablation temperatures, phase evolution during ablation, and ablation morphologies in the different ablation regions consisted of oxidation of the carbon fibre and ceramic matrix, emission of various gases, the flow of high-viscosity SiO2, and denudation of Cf under the erosion of the ablation flame.

Background The ablation therapy for persistent atrial fibrillation (PerAF) is still a challenge due to the high recurrence rate. This study was aimed to investigate the value of extensive linear ablation with contact force sensing techniques for PerAF. Methods A total of 214 patients with PerAF were enrolled in five centers. The patients were randomly assigned to Group I (PVI + LA roof line+ LA anterior wall line) and Group II (PVI + LA roof line), mitral valve isthmus lines were added in both groups if the atrial fibrillation (AF) could not be terminated after all approaches above. Results Acute success rate of AF termination during the ablation procedure in Group I was significantly higher than Group II (P = 0.028). Two-years follow-up showed no significant difference in the sinus rhythm maintenance rate between the two groups (63.4% in group I vs. 57.2% in group II, P = 0.218). More patients in Group I recurred as organized atrial tachycardia (AT) and can be precisely mapped during repeat ablation procedures (15 vs. 2, P = 0.001). The Kaplan–Meier estimates of AF/AT-free survival after repeat ablation procedures were 76.2% in Group I and 47.1% in Group II (P = 0.039). Conclusions Extensive linear ablation with contact force monitoring did not improve the long-term outcomes for PerAF patients. Repeat ablation procedure showed a possible higher chance of sinus rhythm restoration during follow-up.

C/C-SiC-ZrC composites with different ZrC distributions were fabricated using precursor infiltration pyrolysis combined with different drying processes. The microstructural and ablation resistance properties of the composites with different ZrC distributions were investigated. For the C/C-SiC-ZrC composites fabricated using conventional heating-drying, where ZrC particles were largely agglomerated into islands with a dimension range of 10–20 μm, the mass and linear ablation rates under a plasma flame for 60 s were 0.558 mg/s and 16.33 μm/s, respectively. By contrast, for the composites fabricated using freeze-drying, where isolated ZrC particles with a size range of 200–300 nm were uniformly dispersed in the matrix, the mass and linear ablation rates were only 0.078 mg/s and 14.20 μm/s, respectively. This difference in the distribution of ZrC particles led to the difference in ablation resistances, as the uniformly distributed fine ZrC particles were easily oxidized and well dispersed in SiO2 molten glass, which increased the viscosity of the molten glass layer. The high-viscosity SiO2-ZrO2 molten layer covering the surface of the composites effectively prevented the penetration of oxygen and resisted the scour of airflow.

Multi-electrode mapping (MEM) is increasingly applied in ablation of complex atrial arrhythmias. This study aimed to evaluate MEM for analysis and treatment of complex macroreentry atrial tachycardia (MAT).Patients with MAT related to scarring, history of heart surgery or atrial linear ablation were studied. Patients were mapped with conventional activation mapping (CAM) or MEM. After characterizing the mechanism of atrial tachycardia (AT), the ablation was performed.The study consisted of 114 eligible patients, 74 in the CAM and 40 in MEM. Compared with CAM, MEM had a shorter procedure duration (156.7 ± 59.1 ms vs. 127.3 ± 59.3 ms, P = 0.003) and mapping duration (62.6 ± 35.7 ms vs. 30.5 ± 15.3 ms, P 0.001) and more mapping points (1364.9 ± 828.7 points vs. 148.3 ± 79.6 points, P 0.001). There were no significant differences between CAM and MEM in acute ablation success rate, complication, postoperative AADs, and ablation duration. The mean disease-free survival time in CAM versus MEM was 20.8 (95% CI: 17.6-24.1) months versus 26.6 (95% CI: 22.7-30.4) months. The median disease-free survival time in the CAM versus MEM was 20.0 (95% CI: 13.9-26.1) months versus 30.0 (95% CI: 26.7-36.3) months. The AT recurrence risk of MEM was 0.522 times that of CAM (HR 95% CI: 0.282-0.968; P = 0.039).MEM is strongly recommended in ablation of complex MAT.

BACKGROUND The STAR AF II (Substrate and Trigger Ablation for Reduction of Atrial Fibrillation 2) was a multicenter, randomized trial which randomized patients to pulmonary vein isolation (PVI) alone, PVI plus complex fractionated electrograms (CFE), or PVI plus linear ablation (roof line and mitral line). The study failed to show any additional benefit of additional substrate ablation (CFE or lines) in addition to PVI. However, complete block of linear ablations or total elimination of CFE was not achieved in all patients in the adjuvant ablation arms and this could explain why these additive ablation strategies did not improve outcome. We sought to determine whether completeness of adjuvant linear or CFE ablation affected the outcome of these additive ablation strategies when combined with PVI. METHODS AND RESULTS In STAR AF II, 549 patients were randomized 1:4:4 to PVI alone, PVI plus lines, and PVI plus CFE. In this substudy, outcomes of patients with complete linear block and without complete linear block in the PVI + lines group and outcomes for patients with all CFE regions successfully ablated and without all of them ablated in the PVI + CFE are analysed. Of the 243 patients in the PVI plus lines group who received both mitral and roof lines, bidirectional block across both lines was achieved in 179 (74%) but was not achieved in 65 (26%). At 18 months follow-up, AF recurrence occurred in 107 of 179 patients (59.8%) with complete block conduction block across lines and in 40 of 64 patients (62.5%) without complete block (p=0.89) (Figure 1). Even after 2 procedures, AF recurred in 51.9% of patients with complete linear block and 46% of patients without complete block (p=0.09). Of the 207 patients in the PVI plus CFE group who actually underwent CFE ablation, 188 (91%) had elimination of all CFE sites while all CFE were not eliminated in 19 (9%). At 18 months follow-up, AF recurrence occurred in 117 of 188 patients (62.2%) with all the CFE ablated and in 11 of 19 patients (57.9%) without all CFE ablated (p=0.47) (Figure 1). After 2 procedures, AF recurrence occurred in 56.7% of patients with all CFE ablated and 68.0% of patients without all CFE ablated (p=0.29). CONCLUSION PVI combined with both linear and CFE ablation did not result in less AF recurrence compared to PVI alone even after more than one procedure regardless of how well empiric linear or CFE ablation is performed.

Micro-diamond modified C/SiC (C/SiC-D) composites were fabricated using pressureless infiltration (PI) and precursor impregnation and pyrolysis (PIP) methods. The influence of micro-diamond addition on the ablation and mechanical properties of C/SiC composites was discussed. Results show that, compared with C/SiC composites, the thermal conductivity of C/SiC-D composites improves 33.7% due to the good thermal properties of diamond particles and the strong connection with SiC matrix. Meanwhile, C/SiC-D composites exhibit significantly enhanced ablation resistance, with the linear ablation rate decreasing by 43.3%, from 0.030 mm s −1 to 0.017 mm s −1 . The introduction of micro-diamond only brings a limited enhancement to the mechanical properties of C/SiC composites due to the small size and low content of the diamond caused by the limitation of PI method.

A novel HfC precursor and polycarbosilane were combined to fabricate 3-dimensional 4-directional (3D4d) Cf/HfC-SiC composites by precursor impregnation and pyrolysis (PIP). The characterization of HfC precursor demonstrated its suitability for PIP process. Among these 3D4d Cf/HfC-SiC composites, the flexural strength and fracture toughness increased as the SiC/HfC ratio was improved. The 3D4d Cf/HfC-SiC composite (S9-Cf/HfC-SiC) with the highest SiC/HfC ratio of 22.5/11.8 had the high flexural strength of 386.2 ± 50.0 MPa and fracture toughness of 15.9 ± 0.1 MPa m1/2. A typical 3D4d Cf/HfC-SiC composite (S9-Cf/HfC-SiC) was selected for ablation test by oxyacetylene torch and its mass and linear ablation rates were 0.51 ± 0.02 mg cm−2 s−1 and 0.006 ± 0.0002 mm s−1, respectively.

To improve the ablation resistance of carbon/carbon composites at the temperature above 2000 K, a ZrB2-SiC-ZrC ultra-high temperature ceramic coating was prepared by combination of supersonic atmosphere plasma spray (SAPS) and reaction melt infiltration. The micro-holes in ZrB2-Si-ZrC coating prepared by SAPS were effectively filled and the compactness and interface compatibility between the coating and C/C composites was improved through the reaction melt infiltration process. The ultra-high temperature ceramic coating exhibited good ablation resistance under oxyacetylene torch ablation above 2000 K. After ablation for 120 s, the mass and linear ablation rates of the ZrB2-SiC-ZrC coated C/C samples were only −0.016 × 10−3 g/s and 1.30 µm/s, respectively. Good ablation resistance of the ultra-high temperature ceramic coating is mainly attributed to the dense coating structure and the improvement of interface compatibility between the coating and C/C composites.

HfC-SiC coatings have promising applications in the field of ablation protection for carbon-carbon (C/C) composites. In this work, HfC-SiC coatings with different ratios were designed and successfully prepared by low pressure chemical vapor co-deposition using HfCl4-MTS-CH4-H2-Ar system under the guidance of thermodynamic calculations. The phase composition, microstructure, and ablation behavior of HfC-SiC coating with different phase proportions were investigated. The coating with HfC/SiC ratio of 1:1 showed the best ablation resistance after ablation for 90 s, and its mass and linear ablation rates of HfC-SiC coating was only 1.016 ± 0.12 mg/s and 0.998 ± 0.08 µm/s, respectively.

PubMed ID: 29208256 Background: To achieve sinus rhythm, ablation of long-standing persistent atrial fibrillation (LSPAF) usually requires substrate modification in addition to pulmonary vein isolation (PVI). In the present article, we aimed to compare clinical and substrate modification effects of 2 distinct PVI strategies during stepwise ablation in patients with LSPAF: (1) Combined approach: cryoballoon (CB) for PVI and radiofrequency (RF) ablation for substrate modification and (2) RF-only approach: RF ablation for both PVI and substrate modification. Materials and Methods: A total of 34 patients were divided into 2 groups: 19 in the combined group and 15 in the RF group. Left atrial (LA) complex fractionated atrial electrogram (CFAE) maps were acquired before and after PVI and compared between groups. The groups were compared for acute atrial fibrillation termination (AFT) rates and long-term arrhythmia-free survival. Results: A significant reduction on total LA CFAE area was observed with PVI in both groups. In the CB group, when pulmonary veins were excluded, the reduction of LA CFAE area was the most significant on the posterior wall of left atrium and which was greater than in the RF group. Although the ratio of AFT was higher in the CB group (44% versus 33%, respectively), single-procedure arrhythmia-free survival at 1 year was comparable between groups (68% in the CB group versus 66% in the RF group). Times of total procedure, fluoroscopy and post-PVI RF were all shorter in the CB group. Conclusions: CB may cause greater substrate modification on the posterior wall and increase AFT rate during LSPAF ablation. © 2017 Southern Society for Clinical Investigation

To improve the ablation resistance of SiC coating, HfB 2 -SiC coating was prepared on SiC-coated carbon/carbon (C/C) composites by in-situ reaction method. Owing to the penetration of coating powders, there is no clear boundary between SiC coating and HfB 2 -SiC coating. After oxyacetylene ablation for 60 s at heat flux of 2400 kW/m 2 , the mass ablation rate and linear ablation rate of the coated C/C composites were only 0.147 mg/s and 0.267 µm/s, reduced by 21.8% and 60.0%, respectively, compared with SiC coated C/C composites. The good ablation resistance was attributed to the formation of multiple Hf-Si-O glassy layer including SiO 2 , HfO 2 and HfSiO 4 .

C/C-ZrC-SiC composites with different ZrC particle size was fabricated by organic precursor infiltrations and pyrolysis (PIP) combined with additional heat treatment at different temperatures and further PIP of SiC precursor. Effect of ZrC particle size on the ablation resistance of C/C-ZrC-SiC composites was investigated under heat flux of 4.18±0.42MW/m2 containing high scouring. Results showed that small ZrC particle size (0.2μm) caused low viscosity and unfavorable anti-scouring of the formed oxides, leading to unsatisfactory ablation resistance of the composites. Oxides for composites with big ZrC particles (2μm) failed to seal large gaps between ZrC particles, resulting in massive ablation of the composites. Composites with ZrC particle size of around 1μm showed good ablation resistance, with linear ablation rate decreased by 91.3% relative to C/C-ZrC-SiC composites with ZrC particle size of 200nm. The good ablation resistance was mainly ascribed to the formed viscous oxides containing particles, which could resist scouring and meanwhile seal gaps in composites during ablation. Keywords: Carbon/carbon composites, Ablation, Ceramic, Particle size

A bipolar voltage reflects a thick musculature where formation of a transmural lesion may be hard to achieve. The purpose of this study was to explore the association between local bipolar voltage and conduction gap in patients with persistent atrial fibrillation (AF) who underwent atrial roof or septal linear ablation. This prospective observational study included 42 and 36 consecutive patients with persistent AF who underwent roof or septal linear ablations, respectively. After pulmonary vein isolation, left atrial linear ablations were performed, and conduction gap sites were identified and ablated after first-touch radiofrequency application. Conduction gap(s) after the first-touch roof and septal linear ablation were observed in 13 (32%) and 19 patients (53%), respectively. Roof and septal area voltages were higher in patients with conduction gap(s) than in those without (roof, 1.23 ± 0.77 vs 0.73 ± 0.42 mV, p = 0.010; septal, 0.96 ± 0.43 vs 0.54 ± 0.18 mV, p = 0.001). Trisected regional analyses revealed that the voltage was higher at the region with a conduction gap than at the region without. Complete conduction block across the roof and septal lines was not achieved in 3 (7%) and 6 patients (17%), respectively. Patients in whom a linear conduction block could not be achieved demonstrated higher ablation area voltage than those with a successful conduction block (roof, 1.91 ± 0.74 vs 0.81 ± 0.51 mV, p = 0.001; septal, 1.15 ± 0.56 vs 0.69 ± 0.31 mV, p = 0.006). In conclusion, a high regional bipolar voltage predicts failure to achieve conduction block after left atrial roof or septal linear ablation. In addition, the conduction gap was located at the preserved voltage area.

Atypical atrial flutters with clockwise mitral activation usually originate in the left atrium (LA). However, in patients with prior linear ablation for atrial fibrillation (AF), this can be misleading. A 62-year-old female who underwent 3 prior AF ablations, presents for ablation of recurrent

To further improve the ablation resistance of SiBCN ceramics, nanosized HfB2 was introduced by mechanical alloying and subsequent reactive hot-pressing techniques to fabricate HfB2-HfC/SiBCN multiphase ceramics. The mass and linear ablation rates of the 30 vol% HfB2-HfC containing SiBCN ceramics under an oxyacetylene flame for 10 s were lower than those of ZrB2-ZrN/SiBCN and SiBCN, reaching to 0.0025 mg/s and 0.0004 mm/s respectively. Even ablated for 60 s, no trace of cracks appeared on the ablation surface. Oxidation of ceramic matrix, denudation of oxides, erosion by the combustion flow and the re-oxidation of the exposed matrix governed the ablation process.

To improve the oxidation protective ability of carbon–bonded carbon fiber (CBCF) composites, double anti-oxidation protection for CBCF composites were prepared, i.e., ceramic coating-coated CBCF composites combined with ceramic-modified carbon fiber in CBCF matrix. The ablation behavior of modified CBCF composites was tested under an oxyacetylene flame at 1600 °C for 300 s and 800 s, respectively. The results indicate that the ZrB2 in matrix and ZrB2-based ceramic coating can play double protection for CBCF composites during ablation process. The linear ablation rate of the sample after ablation for 300 s and 800 s were −1.1×10−4 and 8.38×10−4 cm s−1, respectively. The modified CBCF composites presented excellent oxidation resistance for 300 s. With the increase of the oxidation time for 800 s, the ZrB2-based ceramic coating experienced catastrophic damage. However, the carbon fiber surface only exhibited some circular pits instead of complete oxidation, implying that the ZrB2 on the carbon fiber surface improved the anti-oxidation and ablation resistance of CBCF composites.

Three-dimensional (3D) braided C/ZrC–SiC composites with various SiC/ZrC ratios were fabricated by precursor infiltration and pyrolysis (PIP) process. The effects of SiC/ZrC ratios on the ablation and mechanical properties were investigated systematically. The flexural strength of 3D C/ZrC–SiC grows with the increase of SiC/ZrC ratios. The compact and stiff ZrC-SiC matrix, moreover, the carbon fiber and PyC interphase with the less reaction damage account for the improved flexural strength of C/ZrC–SiC with higher SiC/ZrC ratios. As for the ablation properties, both mass and linear ablation rates drop with the decrease of SiC/ZrC ratios at the beginning. However, the ablation rates start to increase with the further decrease of SiC/ZrC ratio, where the high open porosity deteriorates the ablation properties. Herein, in order to obtain a balance between ablation and mechanical properties, an appropriate SiC/ZrC ratio should be considered.

To protect carbon/carbon (C/C) composites against ablation, a TaB 2 SiC coating was prepared on their surface by pack cementation. Ablation behavior of the coated C/C composites was investigated under oxyacetylene torch. After ablation for 30 s, the linear ablation rate of the TaB 2 SiC coated C/C composites was 4.2 μm/s. Compared with the SiC coated C/C composites and bare C/C composites, the linear ablation rate was reduced by 40% and 51%, respectively. During ablation, a mosaic-structured Ta Si O glassy layer was formed, playing a positive role in preventing oxidizing species from attacking C/C substrate. Oxidation products of TaB 2 , existing as “pinning phases” in the coating, induced the deflection of the crack formed by the attack of oxyacetylene torch, which was beneficial to enhance the stability of TaB 2 SiC coating and improve the ablation resistance.

Background This study aimed to evaluate an approach for an endpoint of non-inducibility using a combined high-dominant frequency (DF) and continuous complex fractionated atrial electrogram (CFAE) ablation following circumferential pulmonary vein isolation (PVI) in a sequential fashion, including linear ablation as compared to PVI alone. Methods and results A total of 84 non-paroxysmal patients with atrial fibrillation (AF) were investigated retrospectively. The AF patients were divided into two groups: patients with PVI following a combined high-DF and continuous CFAE ablation with linear ablation (substrate modification group, n = 59) and those with PVI alone (n = 25). DF sites of ≥8 Hz and then continuous CFAE sites defined by fractionation intervals of ≤50 ms were modified after PVI. The ablation endpoint was non-inducibility. Atrial tachyarrhythmias (ATs) could not be induced in 54 of 59 (92%) patients after a sequential ablation, and in 18 of 25 (64%) with PVI alone. The ATs freedom without antiarrhythmic drugs in the substrate modification group was significantly greater than that in those with PVI alone after 1 procedure during 12 months of follow-up (78.6% vs. 53.8%, log-rank test p = 0.039). Conclusion This sequential approach using a substrate based ablation was associated with a better clinical long-term outcome as compared to PVI alone.

Porous carbon/carbon composites were infiltrated by Mo–Si–Ti/Al mixed powder to develop a Cf/MoSi2–SiC–C based composites below 1600 °C in this research. Effects of Ti/Al addition on the microstructures and ablation properties of infiltrated samples were investigated and compared together with Si–Mo infiltrated samples. The infiltrated samples are composed of SiC, MoSi2 and ceramic phases containing Ti or Al. Ceramic phases containing Al distribute close to carbon fiber bundles while ceramic phases containing Ti distribute far away from carbon fiber bundles. Samples infiltrated by Mo–Si–Ti showed excellent ablation properties. The linear ablation rate and mass ablation rate after ablated for 300 s under an oxyacetylene torch system are 0.002 mm/s and 0.01 mg/s, respectively. Addition of Al has not improved ablation resistance significantly in this research.

WSi2-HfB2-SiC outer coatings were prepared by in-situ sintering reaction methods. The effect of WSi2 content on the oxidation resistance of HfB2-SiC coating was investigated. The results show that the WSi2-HfB2-SiC coating with 25 wt.% WSi2 (W2) has the best oxidation resistance and can protect C/C substrate for 100 h at 1973 K in air environment. After ablation for 90 s, the linear ablation rate and mass ablation rate of W2 are −3.89 × 10−7 m/s and 6.78 × 10-5 g/s, respectively, showing excellent ablation resistance. The good oxidation and ablation resistance of W2 is attributed to the formation of flowing multiphase glass with inlay.

C/C-ZrC-SiC composites were fabricated by carbothermal reaction of hydrothermal co-deposited oxides and resulted in homogeneous microstructure. The fracture behavior passed from pseudo-plastic to brittle fracture with the increase in ZrC/SiC molar ratios. The composites with a molar ratio of ZrC/SiC≈2:1 presented outstanding ablation resistance with a mass ablation rate of 0.06 mg cm−2 s−1 and a linear ablation rate of 0.13 μm s−1. The optimal ZrC/SiC molar ratio provided a suitable balance of viscosity and flowability of the oxides scale, which not only possessed enough solid ZrO2 to endure the scouring but also had moderate liquid-phase to seal the defects and limited the oxidation.

The ablation properties and mechanisms (under oxyacetylene combustion) together with thermal shock behavior of SiC f /C f /SiBCN ceramic composites were investigated. The solid ablation products are primarily amorphous SiO 2 and cristobalite. The primary ablation mechanisms include fiber and ceramic matrix oxidation, evaporation of B 2 O 3 (l) and SiO 2 (l), and mechanical exfoliation. SiC f /C f /SiBCN has a significantly low mass ablation rate and a desirable linear ablation rate. The combination of crack deflection caused by SiC and carbon fibers, fiber pull-out and debonding improves thermal shock resistance and thus leads to the absence of surface macrocracks.

In order to investigate the ablation behavior and mechanism of carbon/carbon (C/C) composites modified by hafnium carbide (HfC) and silicon carbide (SiC), the composites were ablated by oxyacetylene flame for different time from 30 s to 120 s. Results show that linear ablation rate and mass ablation rate increased with ablation time prolonging. Two ablation regions were discussed: the center-most ablation region which was the most severely ablated and brim ablation region which was only slightly ablated. By analysis of the morphologies evolution of the two regions, it can be demonstrated that ablation products, hafnium oxide (HfO2) and silicon oxide (SiO2), acting as a protection layer for the composites, were produced. While the ablation products lost their protection gradually with ablation time going on. Moreover, mechanical denudation and thermal chemical ablation damaged more severely with ablation time prolonging.

C/C–ZrC–SiC composites coated with ZrC–SiC were prepared by precursor infiltration pyrolysis combined with reactive melt infiltration. The microstructure and ablation behavior of the composites before and after ablation were investigated. The composites exhibit good ablation resistance with a surface temperature of over 2300 °C. After ablation for 120 s, the mass and linear ablation rates of the composites are 0.0045 g/s and 0.0048 mm/s, respectively. The great ablation resistance of the composites is attributed to the formation of continuous integrated SiO2–ZrO2–SiC ceramic layer sealed the pores of the composites surface during ablation.

Ablation mechanism and properties of SiCf/SiBCN ceramic composites under an oxyacetylene torch ablation environment were investigated. Ablation products mainly consist of amorphous SiO2 glass and cristobalite. Four time-dependent ablation actions contribute to the various ablation regions: oxidations of SiC fibers and SiBCN matrix, erosion of SiC fibers in the center region, evaporation of SiO(g) and B2O3(g), and high-viscosity SiO2 liquid flowing with ablation gas-stream. Meanwhile, the mass ablation rate and linear ablation rate of SiCf/SiBCN are notably lower than those of Cf/SiBCN.

Background Although a large isolated surface area of the left atrium (LA) may improve the success rate of catheter ablation (CA) for paroxysmal atrial fibrillation (AF), little is known about the relation between clinical outcomes and the amount of atrial mass reduction (AMR: ratio of total isolated and ablated areas to LA surface area) in different ablation strategies for patients with long-standing persistent AF (L-PeAF). Methods We randomly assigned 119 consecutive L-PeAF patients to adjunctive linear ablation ( n =60) or complex fractionated atrial electrogram (CFAE)-guided ablation ( n =59) after circumferential antral pulmonary vein isolation (PVI). Linear lesions included roof and anterior lines with conduction block. LA defragmentation was performed with an automated CFAE-detection algorithm. Cavotricuspid isthmus block was performed in all patients. Creatine kinase-MB (CK-MB) and troponin-T levels were measured 1day post-CA. Results CK-MB and troponin-T levels were higher, ablation time was longer, and AMR was greater in the CFAE-guided ablation group than in the linear ablation group. AF termination during CA was more frequently observed in the linear ablation group than in the CFAE-guided ablation group ( P =0.031). Twelve months after a single procedure, recurrence occurred in 16 (26.7%) patients with linear ablation and 27 (45.8%) patients with CFAE-guided ablation ( P =0.023). On multivariate analysis, LA volume and ablation method were the only independent risk factors for arrhythmia recurrence. Conclusion Conduction block through linear lines+PVI was an efficient ablation strategy for L-PeAF, whereas the AMR amount did not influence clinical outcomes.

To improve the ablation property, Cu particles were introduced into carbon/carbon (C/C) composites through liquid precursor infiltration combined with in-situ reaction. Compared to pure C/C composites, the modified composites displayed better mechanical property and ablation resistance under oxyacetylene torch when the Cu content was below 8 wt. %. For C/C–Cu composites with 8 wt. % Cu, a 14% decline of linear ablation rate was obtained while defective fibers and laminar matrix survived after ablation. Analyses of ablation behavior depending on ablation time indicated that overflowing of Cu gas weakened the scouring of ablation gas and the Cu gas reduced the partial pressure of oxidizing species, which led to the improved ablation property.

A pulsed laser was used to investigate the ablation behavior and mechanism of C/SiC composite. The results indicated that linear ablation rate of the composite increased with increasing laser power densities and decreased with prolonged ablation time. Three ablation regions were identified on the ablated surface. The ablation center exhibited a needle-like structure with taper-ended carbon fibers standing on the ablation surface filled with some nano-structure carbon sheet. Many spheric SiC particles were deposited in the transitional zone. The ablation edge region was covered by a SiO 2 layer. Furthermore, the ablation mechanisms of different regions were proposed.

Cf/ZrC composites were fabricated at temperatures of 1200–1400 °C by reactive melt infiltration (RMI) using C/C as the preforms and Zr2Cu as the infiltrator. The effects of infiltration time and temperature on microstructure and properties of the composites were investigated. Results show that there was still un-reacted Zr2Cu left in the matrix when the reaction time was not long enough. ZrC grains coarsened and partial Cu evaporated when the time became longer. The infiltration time could be shortened as the infiltration temperature increased, whereas the morphology of ZrC changed from irregular polyhedra to octahedra with faceted surfaces. Composites prepared at 1200 °C for 4 h exhibit superior fracture work (∼103 J/m2) and ablation resistance. The linear ablation rate of the composites is 0.00024 mm/s. Such a low value is attributed to the formation of a ZrO2 protective layer and the cooling mechanism via evaporation of residual Cu in the matrix.

To improve the ablation resistance of carbon/carbon (C/C) composites, a TaC coating was prepared by supersonic plasma spraying on SiC coated C/C composites. The microstructure and morphology of the coatings were characterised by Scanning Electron Microscopy and X-ray diffraction. The ablation properties were studied at different temperatures under oxyacetylene torch. At 2100 °C, the oxides were blown away and resulted in high ablation rates: 1.2×10 −2 mm/s and 3.9×10 −3 g/s. However, most oxides can remain in ablation centre and serve as a coating at low temperature (1900 and 1800 °C). Therefore, the TaC/SiC coated samples exhibited zero linear ablation rate and lower mass ablation rate.

The processing, microstructure and ablative properties of novel phenolic impregnated 3-D Fine-woven pierced carbon fabric ablator (PICA) with different bulk density were investigated. The density of PICA material ranges from 0.352 to 0.701 g/cm3 that having uniform resin distribution within the fibrous substrate. An oxyacetylene torch was used to explore the ablative characteristics in terms of linear/mass ablation rate and microscopic pattern of ablation. Surface and in-depth temperatures during ablation were measured by using optical pyrometers and thermocouples. The experimental results showed that the linear ablation rate varied between 0.019 and 0.036 mm/s and the mass ablation rate increased from 0.045 to 0.061 g/s for the tested PICA composites. It suggests that the PICA composites with lower density may significantly contribute to improving the thermal insulation and ablative properties.

Background Spectral components of atrial fibrillation (AF) other than the dominant frequency (DF) may represent macroreentrant circuits that coexist with higher-frequency sources during AF. Objective The purpose of this study was to determine whether spectral components of AF can be eliminated by targeted linear ablation. Methods Antral pulmonary vein isolation (APVI) and linear ablation were performed in 26 patients (age 60 ± 11 years) to eliminate long-standing persistent AF (duration 3 ± 2 years). Spectral analysis of atrial activation at multiple atrial sites was performed during AF, at baseline, after APVI, and immediately before and after liner ablation along the roof of the left atrium, mitral isthmus, and cavotricuspid isthmus. The prevalence and spatial distribution of spectral components of AF were examined before and after each step of ablation. Results Twelve (46%) of 26 patients had conversion of AF to atrial tachycardia (AT) during ablation. Mean cycle length of AT was 237 ± 25 ms. A spectral component of AF (3.7 ± 1.2 Hz) other than the DF (6.0 ± 0.9 Hz) was present in 74 (43%) of 173 baseline AF periodograms at multiple atrial sites. Following APVI, no difference in the prevalence of spectral components was seen (38% vs 43%, P = .38). However, linear ablation resulted in a significant decrease in the prevalence of spectral components (24% vs 43%, P Conclusion Elimination of spectral components of AF by targeted linear ablation suggests that spectral components may indicate site-specific ATs that coexist with AF despite a lower frequency than the DF of AF.

Background Ablation of long-standing persistent atrial fibrillation (AF) is highly variable, with differing techniques and outcomes. Objective The purpose of this study was to undertake a systematic review of the literature with regard to the impact of ablation technique on the outcomes of long-standing persistent AF ablation. Methods A systematic search of the contemporary English scientific literature (from January 1, 1990 to June 1, 2009) in the PubMed database identified 32 studies on persistent/long-standing persistent or long-standing persistent AF ablation (including four randomized controlled trials). Data on single-procedure, drug-free success, multiple procedure success, and pharmaceutically assisted success at longest follow-up were collated. Results Four studies performed pulmonary vein isolation alone (21%–22% success). Four studies performed pulmonary vein antrum ablation with isolation (PVAI; n=2; 38%–40% success) or without confirmed isolation (PVA; n=2; 37%–56% success). Ten studies performed linear ablation in addition to PVA (n = 5; 11%–74% success) or PVAI (n = 5; 38%–57% success). Three studies performed posterior wall box isolation (n = 3; 44%–50% success). Five studies performed complex fractionated atrial electrogram ablation (n = 5; 24%–63% success). Six studies performed complex fractionated atrial electrogram ablation as an adjunct to PVA (n = 2; 50%–51% success), PVAI (n = 3; 36%–61% success), or PVAI and linear (n = 1; 68% success) ablation. Five studies performed the stepwise ablation approach (38%–62% success). Conclusion The variation in success within and between techniques suggests that the optimal ablation technique for long-standing persistent AF is unclear. Nevertheless, long-standing persistent AF can be effectively treated with a composite of extensive index catheter ablation, repeat procedures, and/or pharmaceuticals.

The ablation of ventricular tachycardia (VT) can be achieved using anatomically guided approaches using differentiated mapping and ablation techniques. The aim of this study was to evaluate the efficacy of limited linear ablation in the VT exit region identified during sinus rhythm mapping alone. One hundred fifteen consecutive patients presenting for ablation of post-myocardial infarction VT were included. After induction of the target VT during invasive electrophysiology, left ventricular substrate mapping during sinus rhythm to identify scar and border zone on the basis of endocardial bipolar voltage was performed. The exit site of the target VT was regionalized by a simplified vector pace mapping approach and targeted using limited linear ablation within the scar border zone. Seventy-seven percent of all inducible VT was successfully ablated. In 71 patients (62%), no sustained VT was inducible at the end of ablation procedure (complete success). During a median follow-up period of 16 + or - 10 months, 89 patients (77%) had no documented sustained ventricular arrhythmia. Seven patients (2%) had recurrences of the initially ablated VT, and 16 (14%) had new-onset VT. Patients with complete success had a significantly lower number of ventricular arrhythmia reoccurrences than patients with incomplete ablation success (11% vs 37%, p = 0.002). In conclusion, postinfarct VT was effectively ablated in 97% of patients without mapping during ongoing VT using a simplified regional linear ablation approach targeting the scar border zone. Freedom from any ventricular arrhythmia was achieved in 77% of patients during midterm follow-up.

Objective To evaluate the electrophysiological characteristics and radiofrequency catheter ablation of atrial tachycardia (AT) in patients with repaired atrial septal defects (ASD). Methods In 76 consecutive patients with AT who underwent the electrophysiological study and radiofrequency catheter ablation (RFCA). 4 patients (one male and three female aged 35.5 ± 11.5 years) had AT-related myocardial scar or incision. Earliest activation combined with entrainment mapping was adopted to determine a critical isthmus. Results Re-entry related to the lateral atriotomy scar was inducible in 3 of 4 patients. With entrainment mapping, the PPI-TCL difference was Conclusion Under conventional electrophysiological mapping, adopting linear ablation from scar area to anatomic barrier, successful ablation also can be obtained in patients with IRAT related to myocardial scar or incision.

Background The optimal technique for producing linear radiofrequency thermal lesions in myocardial tissue is unclear. We compared epicardial ablation on the beating heart with endocardial ablation after cardioplegia. Methods Radiofrequency lesions were produced using a multielectrode malleable handheld probe in ovine myocardium with three wall thicknesses. Detailed analysis of lesion dimensions was used to assess the effects of site of ablation, muscle thickness, and duration of ablation. Results After epicardial atrial ablation, myocardial lesions were detected in all sections without macroscopically visible epicardial fat (n = 10), but only 43% (6/14) of sections with epicardial fat. Three of 24 atrial epicardial sections (13%) and 92% (23/25) of endocardial atrial lesion sections were clearly transmural. In thicker tissues lesion depth was independent of endocardial (right ventricle: 3.9 ± 1.1 mm, left ventricle: 3.8 ± 0.7 mm) or epicardial (right ventricle: 3.4 ± 0.6 mm, left ventricle: 4.3 ± 0.9 mm) ablation site. Epicardial lesions are less deep in thinner areas of myocardium ( p = 0.003). Lesions were all wider than they were deep. There was no significant increase in lesion depth with the increase in ablation duration from 1 to 2 minutes. Conclusions Lesions were unlikely to be transmural with either technique when the wall thickness was greater than about 4 mm. Epicardial fat has an important negative effect on epicardial lesion formation. Where epicardial fat is absent epicardially produced lesions penetrate less deeply when the wall thickness is small, possibly due to endocardial cooling by circulating blood. Prolongation of the duration of ablation from 1 to 2 minutes does not significantly increase lesion depth.

Introduction Atrial fibrillation ablation success rate has improved over the years. Data regarding success rate with contact force catheter are only available in clinical trials. The aim of our study was to assess the “real-life” success rate of atrial fibrillation ablation at 1 year using the Smarttouch catheter (Biosense Webster). Methods Patients who underwent first procedure of atrial fibrillation ablation between January 2014 and December 2015 were prospectively enrolled. Patients with paroxysmal atrial fibrillation (PAF) underwent pulmonary vein isolation. Patients with persistent atrial fibrillation (PeAF) had pulmonary vein isolation with linear ablation and/or atrial defragmentation to obtain sinus rhythm. Procedure success rate was defined as free from any arrhythmia during the first year of follow-up. Results Overall, 246 patients (62.6 ± 11 year, 68% males) were enrolled in our study. One hundred and forty eight patients underwent PAF ablation and 99 patients underwent PeAF ablation. Among the PAF patients, 26 had atrial arrhythmias during follow-up (success rate 82.4%). Among the PeAF patients, 33 had atrial arrhythmias during follow-up (success rate 66,6%). Interestingly, 29.79% of patients with no arrhythmia recurrence were still on antiarrhythmic drugs despite our recommendations to stop them at 3 months after the procedure. Conclusion After a single atrial fibrillation ablation with contact force catheter (Smarttouch, Biosense webster), real-life success rate is consistent with clinical trials. Some patients without arrhythmia recurrence were still on antiarrhythmic drugs despite electrophysiologists recommendations.

A three-dimensional C/C-HfC composite with a density of 1.95 g/cm3 was fabricated by chemical vapor infiltration of carbon into a 3D woven carbon fiber felt to a density of 1.45 g/cm3 followed by vacuum impregnation and pyrolysis of a solution containing the HfC precursor.Results indicate that HfC particles are uniformly dispersed around the pyrocarbon.The 3D C/C-HfC composite exhibits a good ablation resistance at 2573 K.The mass and linear ablation rates after ablation for 120 s are 0.001 5 g/s and 0.002 4 mm/s,respectively.The resistance to ablation is attributed to the introduction of HfC into the C/C composite.The tree-coral-like HfO2 particles formed during the ablation act as thermal and oxygen diffusion barriers,protecting the composite from further ablation.Also,the oxidation of HfC and the volatilization of the ablation product (CO) absorb a large amount of heat from the composite.

1) to estimate theoretical probability of 4- and 6-waves re-entry to eliminate as a results of linear ablation simulation in 2D-mathematical modeling of left atrium (LA); 2) to extrapolate mathematical modeling data to clinical results of linear ablation in patients with paroxysmal and persistent AF

Since the first report of radiofrequency catheter ablation curing atrial fibrillation (AF) nearly a decade ago [(1)][1], numerous techniques have evolved, from linear ablation to modify the reentrant substrate for AF [(1,2)][1], to electrical isolation of pulmonary vein(s) to eliminate triggers of

Radiofrequency catheter ablation (RFCA) is effective for rhythm control in longstanding persistent atrial fibrillation (L-PeAF); however, long-term recurrence is observed. We explored whether changes in P-wave morphology on electrocardiography (ECG) is related to the long-term recurrence of AF after

The evolution of effective and broadly applicable strategies for percutaneous ablation of atrial fibrillation (AF) has followed a complex course over the past decade. In 1994, Swartz et al. [(1)][1]reported successful percutaneous ablation of AF with multiple long linear lesions. Conceived as a

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