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The ablation properties of C/C-ZrC-SiC composites prepared by precursor infiltration and pyrolysis processes were studied by the H2-O2 ablation method. The results indicate that the ablation rate of C/C-ZrC-SiC composites decreases with increasing density of the composites. The linear ablation rate and mass ablation rate of the C/C-ZrC-SiC composites (ρ=1.69g·cm-3) were 0.00211mm·s-1 and 0.5179mg·s-1, only 20.6% and 31.6% of those of C/C composites (ρ=1.78g·cm-3) respectively. The introduction of ZrC-SiC into the matrix greatly enhanced the anti-oxidative and ablation property of the C/C composite. The ablation mechanisms of the C/C-ZrC-SiC composites were supposed to be the synergistic effects of thermo-chemistry ablation (oxidation and sublimation) and mechanical erosion.

This study focuses on the conditions of preparation of C/C-SiC composites through polymer infiltration and pyrolysis method using hydrogen-containing polysiloxane as the precursor and divinylbenzene as cross-linking agent. The densities of different C/C composites (ρ=1.02, 1.21, 1.60, 1.78g·cm-3) increased to 1.24, 1.36, 1.69, 1.84g·cm-3respectively after infiltration and pyrolysis four times. The appropriate ratio of hydrogen-containing polysiloxane and divinylbenzene was 1/0.5. The appropriate cross-linking temperature was 250°C. In pyrolysis process, the appropriate increasing rate of pyrolysis temperature should be 50°C/h in the range of 300-800°C. SiC was formed when pyrolysis temperature reached 1550°C.The linear ablation rate and mass ablation rate of C/C-SiC composites were much lower than those of C/C composites.

Atrial fibrillation (AF) is an arrhythmia associated with increased morbidity and mortality. Since the first report of catheter ablation curing AF, numerous techniques have evolved, from linear ablation to segmental pulmonary vein (PV) isolation, to extensive encircling PV isolation, to left atrial (LA) linear ablation, to ablation of complex fragmented atrial electrograms (CFAEs) and ablation of ganglionated plexi. A new approach for complete isolation of the posterior LA, including all PVs, is box isolation. PV isolation is associated with a high clinical success rate in paroxysmal AF. However, in persistent AF or longstanding persistent AF, PV isolation only may not be sufficient, so additional ablation at sites with CFAEs is needed to improve the clinical outcome. A hybrid approach of combining PV isolation plus CFAE ablation is highly effective in the majority of patients with persistent AF or longstanding persistent AF. Thus, AF ablation is an effective and established treatment for AF that offers an excellent chance of a lasting cure. It is about time that AF ablation became a first-line therapy for selected patients with AF. (Circ J 2011; 75: 2305-2311)

Since the first report of catheter ablation curing atrial fibrillation (AF), numerous techniques have evolved, from linear ablation to segmental pulmonary vein (PV) isolation, extensive encircling PV isolation, LA linear ablation, ablation of complex fragmented atrial electrograms (CFAE) and stepwise ablation. We developed a new approach for complete isolation of the posterior LA including all PVs, namely box isolation. In the post erior LA, there are many arrhythmogenic substrates for AF, including the triggers, reentries and ganglionated plexi. Box isolation can contain these abnormal substrates in the posterior LA. Box isolation is associated with a high clinical success rate in paroxysmal AF. However, in persistent AF or longstanding persistent AF, only box isolation may not be sufficient, therefore, additional ablation at sites with CFAE outside the box area is needed to improve the clinical outcome. A hybrid approach of combining box isolation with CFAE ablation is highly effective in the majority of patients with persistent AF or longstanding persistent AF. Thus, AF ablation is an effective and safe treatment for AF that offers an excellent chance for a lasting cure.

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.

Comparison of Radiofrequency Versus Conventional Catheter Ablation. Introduction: Radiofrequency (RF) catheter ablation has been established as an effective and curative treatment for atrial flutter (AFL). Approved methods include a drag-and-drop method, as well as a point-by-point ablation technique. The aim of this study was to compare the acute efficacy and procedural efficiency of a multipolar linear ablation catheter with simultaneous energy delivery to multiple catheter electrodes against conventional RF for treatment of AFL. Methods: Patients presenting to our department with symptomatic, typical AFL were enrolled consecutively and randomized to conventional RF ablation with an 8-mm tip catheter (ConvRF) or a duty-cycled, bipolar-unipolar RF generator delivering power to a hexapolar tip-versatile ablation catheter (T-VAC) group. For both groups, the procedural endpoint was bidirectional cavotricuspid isthmus block. Results: Sixty patients were enrolled, 30 patients each assigned to ConvRF and T-VAC groups. Total procedure time (40.2 ± 15.8 min vs 60.5 ± 12.7 min), energy delivery time (8.5 ± 3.7 min vs 14.7 ± 5.2 min), radiation dose (14.5 ± 3.5 cGy/cm2 vs 31.7 ± 12.1 cGy/cm2), and the minimum number of RF applications needed to achieve block (4.2 ± 2.4 vs 8.9 ± 7.2) were significantly lower in the T-VAC group. In 7 patients treated with the T-VAC catheter, bidirectional block was achieved with less than 3 RF applications, versus no patients with conventional RF energy delivery. Conclusion: The treatment of typical AFL using a hexapolar catheter with a multipolar, duty-cycled, bipolar-unipolar RF generator offers comparable effectiveness relative to conventional RF while providing improved procedural efficiency. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1109-1113)

ZrB2-SiC and ZrB2-SiC-C ultra-high temperature ceramics (UHTCs) were fabricated by pressureless sintering under an argon atmosphere. The mass and linear ablation rates were tested in an oxyacetylene flame with high velocity. The microstructure and phase transformation of the ZrB2-based UHTCs were characterized by scanning electron microscopy along with energy dispersive spectrometry. Results show that the UHTCs have excellent properties of ablation resistance at ultra-high temperature. The values of mass and linear ablation rates were lower in the ZrB2-SiC UHTCs than those measured for ZrB2-SiC-C. The effect of C addition on the ablation resistant was not obvious but it influenced the microstructure of the ZrB2-SiC UHTCs. And the ablation resistant mechanisms of ZrB2-based UHTCs were discussed according to microstructure analysis.

In order to monitor lead pollution from urban areas to coral reefs in the Gulf of Thailand, linear and two-dimensional distributions of Pb in corals from Khang Khao Island, Thailand and Rukan-sho, Okinawa, were analysed with high resolution. Laser ablation inductively coupled plasma mass spectrometry was applied to measure Pb content in coral skeletons using synthetic Pb standards in a CaCO3 matrix as calibration materials. Linear and two-dimensional ablation schemes were applied to determine the Pb content in corals collected from Khang Khao Island, Thailand and Rukan-sho, Okinawa. The coral skeleton was ablated by Nd:YAG laser (wavelength of 266 nm, beam diameter of 155 µm, scanning speed of 10 µm s−1 and frequency of 10 Hz) along the growth axis, and ion counts for 208Pb were normalised to 42Ca. Lead content in the corals was determined using a calibration curve obtained from the synthetic Pb standards (0–141 µg g−1). The linear ablation track of the sample from Khang Khao showed over 30 peaks of Pb with an average value of 3.55 µg g−1, while Pb content in the coral from Rukan-sho showed relatively small variation with an average value of 0.132 µg g−1. Two-dimensional imaging of Pb in the coral skeletons was also carried out for an area of 7 × 20 mm on the sample from Khang Khao. The distribution patterns of Pb and Ba in the Thailand coral co-varied. These observations from the linear and imaging analyses suggest discontinuous inputs of anthropogenic Pb from rivers to the Gulf of Thailand.

Background: The left atrial (LA) size is an important predictor of atrial fibrillation (AF) procedural termination and the long-term outcome. We sought to evaluate the long-term outcome in regard to the LA size and procedural termination. Methods: Eighty-seven consecutive chronic AF patients (72 males, 53 ± 10 years) underwent 3D mapping (NavX) and ablation. A stepwise approach including circumferential pulmonary vein (PV) isolation, linear ablation, and continuous complex-fractionated electrogram (CFE) ablation (targeting fractionation intervals of < 50 ms). Electrical cardioversion was applied to those without any procedural termination. The freedom from AF was defined as the maintenance of sinus rhythm without the use of any class I or III antiarrhythmic drugs after the blanking period. Results: Among the 87 patients, all received a circumferential PV isolation, 93% a linear ablation, and 59% a continuous CFE ablation. Those with AF procedural termination (n = 30) had a better long-term outcome when compared with those without termination during a follow-up of 21 ± 12 months. Moreover, a Kaplan-Meier analysis showed that in those with an LA diameter of less than 45 mm (n = 49), the freedom from AF rate was higher when procedural termination was achieved (P = 0.004). On the contrary, the outcome was comparable in those with an LA diameter of ≥ 45 mm (n = 38), whether AF procedural termination occurred or not (P = 0.658). Conclusions: AF procedural termination was related to the long-term success during chronic AF ablation, especially in those with an LA diameter of less than 45 mm. The favorable effect of termination decreased when the LA diameter was ≥ 45 mm.

The results of the elaboration, testing, and application (in bench studies) of fiber sensors of linear ablation of a heat shield material are presented. The measuring technique and the structural arrangement of the sensors designed for products of the research and production association (RPA) “Energiya” and the design office “Novator” (Russia) have been described. Methods for manufacturing a ceramic tip equipped with fiber ablation sensors have been developed.

Substrate modification guided by CARTO system has been introduced to facilitate linear ablation of ventricular tachycardia (VT) after myocardial infarction (MI). However, there is no commonly accepted standard approach available for drawing these ablation lines. Therefore, the aim of the present study was to practically refine this time consuming procedure.

Catheter ablation of atrial fibrillation (AF) has evolved over the past 20 years from being a novel, unproven procedure to a commonly performed procedure. Triggers are important for the initiation of AF and a suitable substrate is important for perpetuation of AF. Remodeling, including electrical and structural remodeling, is common in patients with persistent AF. Therefore, targeting the remodeled atrium is a critical issue during persistent AF ablation. However, ablation outcomes remain suboptimal despite aggressive substrate modification. Empirical linear ablation is not recommended because of the difficulty in achieving complete linear block and it is recommended only if macroreentry tachycardia develops during the procedure. Complex fractionated atrial electrogram (CFAE) ablation is recommended in the Heart Rhythm Society Consensus Document but efficacy has been limited in long-term follow-up studies. Rotor ablation is controversial. A combined approach using CFAE, similarity and phase mappings with rotor identification may be helpful in searching for AF sources and subsequent substrate ablation. Nevertheless, more prospective randomized studies are required to validate efficacy and safety.

For composites under gradient heating up to very high temperatures 1500 – 2000 °C, linear (surface) ablation must be considered in addition to volumetric ablation. The definitions and classification of linear ablation processes were given in paragraph 1.2. The purpose of the present chapter is to establish relationships for the calculation of the linear rate D for different types of surface ablation: combustion, sublimation, melting and thermomechanical erosion of composites.

This chapter is devoted to a brief description of methods of experimental determination of composite material properties under high temperatures. The following parameters are considered: density \(\rho (\theta )\) under heating; heat conductivity \(k_\alpha (\theta )\) under heating; gas-permeability K under heating; heat deformations \(\overset{\circ }{\varepsilon }_\alpha (\theta )\) under heating; elastic moduli \(E_\alpha (\theta )\) under heating; strength \(\sigma _{\alpha T} (\theta )\) under heating; linear ablation rate D of composites under nonuniform heating. The data obtained by experiment are given in Chaps. 4– 13 of the book.

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.

Curing atrial fibrillation (AF) by catheter ablation has significantly improved patient morbidity and mortality. The circumferential pulmonary vein isolation technique is established as the principal procedure, with a high cure rate and acceptable safety, for paroxysmal AF, but new adjunctive ablation strategies targeting the AF substrates and sources for long-standing persistent/chronic AF have been developed. These new techniques include linear ablation, complex fractionated atrial electrogram guided ablation, dominant frequency map-guided ablation, ganglionated plexi ablation and disconnection of the coronary sinus and superior vena cava to ablate the AF substrates and sources. The long-term usefulness of the established technique and these innovative adjunctive approaches for the treatment of AF remains to be investigated.

There is ongoing debate regarding the precise mechanisms underlying atrial fibrillation (AF). An improved understanding of these mechanisms is urgently needed to improve interventional strategies to suppress and eliminate AF, since the success of current strategies is suboptimal. At present, guidelines for AF ablation focus on pulmonary vein (PV) isolation for the prevention of arrhythmia. Additional targets are presently unclear, and include additional linear ablation and electrogram-guided substrate modification, without clear mechanistic relevance. PV and non-PV triggers are likely central in the first few seconds of AF initiation. Rapid activation from such triggers interacts with transitional mechanisms including conduction velocity slowing, action potential duration (APD) alternans, and steep APD restitution to cause conduction block and initiate functional reentry. However, complete suppression of potential triggers has proven elusive, and the intra-procedural mapping and targeting of transitional mechanisms has not been reported. A growing body of research implicates electrical rotors and focal sources as central mechanisms for the maintenance of AF. In several recent series, they were observed in nearly all patients with sustained arrhythmia. Ablation of rotor and focal source sites, prior to pulmonary vein isolation, substantially modulated atrial fibrillation in a high proportion of patients, and improved ablation outcomes versus pulmonary vein isolation alone. These results have subsequently been confirmed in multicenter series, and the improved outcomes have been found to persist to a mean follow-up of 3 years. Recently, rotors have been observed by multiple groups using diverse technologies. These findings represent a paradigm shift in AF, focusing on sustaining mechanisms, as is currently done with other arrhythmias such as atrioventricular node reentrant tachycardia. Studies are currently underway to assess the optimal strategy for the application of rotor-based ablation in AF management, including clinical trials on the relative efficacy of rotor-only ablation versus PVI-only ablation, which will inform future practice guidelines.

AIMS The aim of this study was to reveal the incidence, location, and cause of recovery of the electrical connections (ECs) between the left atrium and the pulmonary veins (PVs) after the segmental ostial PV isolation (PVI). METHODS AND RESULTS Pulmonary vein mapping and successful PVI were performed using a computerized three-dimensional mapping system (QMS2trade mark) with a basket catheter in 167 PVs in 53 consecutive patients with atrial fibrillation (AF). In 14 patients with recurrent AF after PVI, the same PV mapping and isolation as in the first procedure were performed, and the PV potential maps constructed by QMS2 in two different procedures were compared. Forty-nine recovered ECs were observed in 27 PVs, and all were eliminated by a few local radiofrequency (RF) applications. Thirty-four (69%) of those ECs recovered at the edge of original ECs, and another 15 (31%) recovered at the mid-portion of the continuous broad original ECs. CONCLUSION Electrical connection recovery occurred most commonly at the edges of original ECs and occasionally at the mid-portion of continuous broad original ECs after PVI probably due to tissue oedema neighbouring the segmental RF lesions. Further RF lesions at the edge of original ECs and linear ablation to the continuous broad ECs may help reduce AF recurrence.

Linear left atrial ablation is performed in combination with pulmonary vein (PV) isolation to improve the clinical results of atrial fibrillation (AF) ablation. These procedures require long procedures and fluoroscopic exposure. The aim of the present study was to evaluate the performance of a new, nonfluoroscopic, real-time, three-dimensional navigation system for linear ablation at the left atrial roof and mitral isthmus. The study included 44 patients (54 +/- 10 years of age, 5 women) with drug-refractory AF, who underwent roof line or mitral isthmus linear ablation after 4-PV isolation. In 22 patients, ablation was performed with the navigation system (test group), and in the remainders linear ablation was performed with fluoroscopic guidance alone (control group). Conduction block was achieved in 20 patients (91%) in test group, and 21 patients (95%) in the control group (ns). Use of the navigation system was associated with a shorter fluoroscopic exposure for roof line (5.6 +/- 3.0 minutes vs 8.7 +/- 5.0 minutes, P < 0.05), and a trend for mitral isthmus ablation (7.8 +/- 7.8 minutes vs 12.1 +/- 5.9 minutes). It was also associated with a trend toward shorter procedure times for roof line (15.3 +/- 8.6 minutes vs 22.9 +/- 16.8 minutes) and mitral isthmus line (20.2 +/- 15.8 minutes vs 32.0 +/- 7.6 minutes) but no difference in duration of radiofrequency delivery. There was no procedural complication. The use of this new nonfluoroscopic imaging system was associated with a shorter fluoroscopic exposure as well as a trend toward shorter duration of linear ablation procedures for AF.

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.

Mapping strategies for ventricular tachycardia (VT) have evolved significantly in the past 2 decades. This review discusses mapping techniques that can help in successful VT ablation. The electrocardiogram (ECG) remains a vital component of VT mapping and can help to identify the chamber of origin of VT. The ECG morphology of VT, however, is influenced by orientation of heart and location of the scar. Activation mapping during VT is an important technique that can help in further localization. Care has to be exercised to ensure that small signals are not ignored and far-field signals are recognized. Pace-mapping to mimic the VT is another way to map exit site for scar based reentrant VT or the site of origin of triggered and automatic VT in the absence of structural heart disease. For the latter group, this technique is widely used in determining the site of ablation. It is important to ensure a complete ECG match (12 out of 12 leads) of the pace-map to the clinical arrhythmia in these patients. In patients with structural heart disease, entrainment mapping remains the gold standard for defining the protected isthmus and other components of the VT circuit. Using this technique, successful ablation of reentrant VT can be achieved in 60-90% of patients. In order to perform entrainment mapping, the VT has to be hemodynamically tolerated; this is not the case in 25% of pts with scar based reentrant VT. The development of 3-dimensional mapping systems allows for more anatomically based linear ablation in patients with poorly tolerated uniform VT. Despite these advances, there are still about 10-20% VTs that cannot be ablated successfully with the above described techniques, especially in patients with structural heart disease. Other recent advances such as percutaneous closed chest epicardial mapping technique and cooled tip ablation catheter technology have the potential to enhance mapping and successful ablation of VT.

Background: Catheter based “maze” procedures for atrial fibrillation have been hampered by difficult creation and evaluation of continuous and transmural linear lesions. Our aim was to develop an online evaluation method for effective lesion creation based on conventional techniques and using the multipolar ablation catheter, already in place.

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

Persistent left superior vena cava (LSVC), an uncommon venous anomaly, could be an arrhythmogenic source of atrial fibrillation. Multiple electrical connections were reported between the LSVC and the left atrium, which may negatively impact the achievement of conduction block during linear ablation of left mitral isthmus. We describe a case with perimitral atrial flutter (AFL) in a patient with isolated LSVC. AFL was successfully treated and complete perimitral conduction block was achieved following a lengthy epicardial radiofrequency application.

This editorial refers to ‘Electrical isolation of substrate after myocardial infarction: a novel ablation strategy for unmappable ventricular tachycardias—feasibility and clinical outcome’ by R. R. Tilz et al ., on page 1041 . Radiofrequency (RF) catheter ablation of ventricular tachycardia (VT) has become an important part of the therapeutic armamentarium for treating ventricular arrhythmias in patients with structural heart disease.1 Catheter ablation has proven to control arrhythmic storm and reduce shocks in implantable cardioverter-defibrillator (ICD) recipients with ventricular arrhythmia episodes.2 Novel VT catheter ablation techniques have been developed to overcome the limitations of conventional mapping and ablation. These new techniques aim to characterize and eliminate the arrhythmogenic substrate during stable rhythms. In addition, the advent of three-dimensional non-fluoroscopic systems that allow a detailed electroanatomic reconstruction of the ventricles has facilitated the development of substrate-guided ablation. However, despite improvements in the ablation technology, the rate of recurrence after ablation remains high.3 Based on the surgical experience, Marchlinski et al .4 proposed targeting scar border zone tissue areas with bipolar voltage from 0.5 to 1.5 mV. The best ablation design was considered the creation of ‘linear ablation lines’ transecting the dense scar (

Purpose Catheter ablation of atrial fibrillation (AF) is now one of the most frequently performed ablation procedures, but there are currently 2 important challenges: achieving permanent/durable rather than transient pulmonary vein isolation (PVI) and improving the results of ablation for the wider patient population with persistent AF. Methods Recent technical advances in the technique of ablation and the results of clinical trials aimed at achieving more permanent and durable PVI are reviewed. We also summarize recent advances in identifying atrial fibrosis and in understanding the pathophysiology of AF relevant to selecting patients for ablation of persistent AF. Findings The use of contact force–sensing technology, adenosine testing after ablation, and pace capture–guided ablation all have the potential for achieving more durable ablation. Selection of patients suitable for ablation of persistent AF may be improved by assessing the extent of atrial fibrosis with delayed enhancement imaging with cardiac magnetic resonance or by assessing the pattern of atrial electrical activity with the use of complex atrial electrograms. Advances in treatment are likely to result from the recognition of localized rotors and focal sources as primary sustaining mechanisms for all types of human AF and in the use of noninvasive mapping for their identification. Linear ablation to supplement PVI may improve the results of AF ablation. Implications Rapidly unfolding advances in the techniques of AF ablation and the understanding of mechanisms of AF hold promise for improving the durability of PVI and for extending the technique to carefully selected patients with persistent AF.

The ablative formation of deep channels in steel by femtosecond and picosecond laser pulses is studied. A significant screening of the incident energy inside deep channels is found to occur due to the air breakdown at ablated microparticles. The breakdown thresholds and the microparticle precipitation times are estimated. This kind of plasma screening stabilises the linear ablation rate and causes a significant channel broadening.

Objectives: To characterize the electrophysiologic and histologic sequelae of linear atrial ablation utilizing an irrigated electrode. To compare “irrigated” lesions with lesions deployed using the same electrode in a non-irrigated mode. Background: Previous reports of radiofrequency catheter ablation using an irrigated electrode have emphasized its favorable effect on lesion depth. We hypothesized that electrode irrigation would also benefit linear ablation of smooth atrial myocardium, a relatively superficial target. Methods: In healthy pigs, lesions were deployed in the right and left atria. Acutely, lesions resulting from ablation using an irrigated electrode, with radiofrequency energy titration guided by electrogram amplitude reduction, were compared to lesions using the same electrode without irrigation, with energy titration guided by electrode thermometry. Irrigated lesions were also assessed serially. Results: Acutely, irrigated lesions formed complete conduction barriers and were uncomplicated. In contrast, non-irrigated lesions formed complete conduction barriers but were frequently complicated, exhibiting endocardial charring, barotrauma, and pericardial damage. The rate and pattern of histologic evolution of irrigated lesions were uniform throughout each lesion; right and left atrial lesions healed similarly. During healing, 90% of lesions remained complete conduction barriers and 10 % manifested single discrete conduction gaps where viable appearing myocytes bridged the lesion. Conclusions: Complete, uncomplicated linear lesions could be reliably deployed in either atrium with an irrigated electrode. Not all lesions remained complete barriers to conduction during their histologic evolution. Lesions deployed with the same electrode ina non-irrigated mode were complete but frequently complicated.

Pre-ablation impedance was evaluated for its ability to detect electrode-tissue contact and allow creation of long uniform linear lesions with a multi-electrode ablation catheter. The study consisted of 2 parts, both of which used the in vivo pig thigh muscle model. In part 1, a 7 Fr. multi-electrode catheter was held in 3 electrode-tissue contact conditions: (1) non-contact; (2) light contact with a 30[emsp4 ]g downward force; and (3) tight contact with a 90[emsp4 ]g downward force. Impedances were measured in unipolar, modified unipolar and bipolar configurations using a source with frequencies from 100[emsp4 ]Hz to 500[emsp4 ]kHz. Compared with non-contact, the impedance increased 35±22±% with 30[emsp4 ]g contact pressure and 68±40±% when the contact pressure was increased to 90[emsp4 ]g across the range of frequencies studied. In part 2, the same catheter was held against the tissue with different forces. Pre-ablation impedance was measured using a 10[emsp4 ]kHz current. Phased radiofrequency energy was applied to the 5 electrodes simultaneously using 10[emsp4 ]W power at each electrode for 120[emsp4 ]s. A total of 32 linear lesions were created. The lesion dimensions correlated with pre-ablation impedance. A unipolar impedance ≥190[emsp4 ]Ω indicates 95±% possibility to create a uniform linear lesion of at least 3[emsp4 ]mm depth with our ablation system. We conclude that pre-ablation impedance may be a useful indicator for predicting electrode-tissue contact and the ability to create a continuous and transmural linear lesion with a multi-electrode catheter.

Within the past years, refinements in electrophysiologic mapping techniques have provided a clear understanding of typical and atypical atrial flutter circuits. 1 2 3 Catheter mapping studies have indicated that a common myocardial “isthmus” between the inferior tricuspid annulus (TA) and the inferior caval vein is an integral part of the circuit in typical flutter. Linear lesions induced with radiofrequency (RF) catheter ablation have cured the arrhythmia by producing an electrically insulated barrier within this isthmus 4 ; thereby, isthmus ablation is the technique that has introduced the strategy of linear ablation instead of focal ablation as used for ablation of accessory pathways. In the current electrophysiologic laboratories, ablation of atrial flutter is the most frequent indication for ablation. This is supported by a recent population-based investigation of atrial flutter, suggesting that this arrhythmia is much more common than previously supposed with an estimated 200,000 new cases annually in the United States. 5 A prospective randomized comparison of antiarrhythmic therapy versus first-line RF ablation in patients with atrial flutter indicated that in selected patients, RF ablation could be considered a first-line therapy because of better success rates, a positive impact on quality of life, a lower occurrence of atrial fibrillation, and a lower need for rehospitalization at follow-up. 6 In our center, the recurrence of symptomatic or hemodynamically significant atrial flutter leads to an indication for ablation.

Linear left atrial (LA) ablation in patients with persistent atrial fibrillation (PsAF) resulting in the elimination of most complex fractionated electrogram (CFE) sites has been demonstrated. This study was designed to evaluate the impact of a localized CFE ablation in addition to a representative linear LA ablation in patients with PsAF.A total of 40 consecutive patients with PsAF underwent construction of CFE and dominant frequency (DF) maps using NavX. A stepwise linear ablation including at the PV antra, septum, roof, mitral annulus, and ridge of the appendage was performed followed by additional ablation of localized CFEs detected by an automatic algorithm.A significant reduction in the continuous CFE burden (50 ms) after the linear ablation (69 vs. 21 %; P 0.0001) was confirmed, and localized CFEs (40-120 ms) were observed with a significant predilection for the anterior (30 %), posterior (30 %), and inferior LA (38 %) regions (P 0.01). Comparing the localized CFEs with higher frequency sources, 45 % (70/156) of the localized CFE sites included continuous CFE regions, and 59 % (92/156) of those sites overlapped with the high-DF sites (8 Hz). Additional localized CFE-targeted ablation further terminated PsAF in 20 % of the patients and further increased the mean CFE cycle length (110 ± 31 to 125 ± 39 ms; P = 0.0033) and decreased the DF (6.0 ± 0.8 to 5.7 ± 0.7 Hz; P = 0.0013) within the CS.The presence of localized CFE sites with a predilection for particular LA regions after a representative linear LA ablation could provide the optimal sites for selective substrate modification of the atrial fibrillation substrate in patients with PsAF.

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

After previous pulmonary vein isolation and left atrial linear ablation for persistent atrial fibrillation (AF), a 70-year-old woman was referred for a redo procedure due to paroxysmal AF not controlled with antiarrhythmic drugs. Catheter movement induced AF that spontaneously went into an …

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

Introduction We describe the use of a ablating system to compartmentalise and regionally isolate the atria in paroxysmal and persistent atrial fibrillation (AF). Methods 40 patients were studied, 25 paroxysmal AF and 14 persistent AF. One patient enrolled was later found to be in left atrial flutter and was excluded. The Cardima Revelation® TX catheter system with Intellitemp® Radiofrequency (RF) energy control device and a Medtronic Atakar® RF generator were used to place wide area circumferential ablations to achieve conduction block into the left and right sided pulmonary veins. Roof lines and mitral isthmus lines were also performed. In patients with persistent AF and in repeat procedures, right atrial compartmentalisation was performed with an anterior superior vena cava (SVC) to inferior vena cava (IVC) line and a septal SVC to IVC line. Results At 6 months, 18 of the 39 patients were asymptomatic, 10 had improved symptoms and 22 were in sinus rhythm. In the paroxysmal group, 11 were asymptomatic, 7 had improved symptoms and 16 (64%) were in sinus rhythm. In the persistent group, 7 were asymptomatic, 3 had improved symptoms and 6 (43%) were in sinus rhythm. The total group AF burden was 37.8 ± 5.4 hrs pre-procedure and 23.1 ± 5.1 hrs at 6 months post procedure. Mean temperature, impedance and power recorded at each pole demonstrated effective power delivery at all poles. No catheter charring was observed, complication rates were comparable to standard AF ablation technique. Conclusion Linear ablation in the left and right atria to mimic Cox’s Maze is feasible and safe using this ablating system.

UNLABELLED PV and Linear Ablation for CFAEs. INTRODUCTION Linear ablations in the left atrium (LA), in addition to pulmonary vein (PV) isolation, have been demonstrated to be an effective ablation strategy in patients with persistent atrial fibrillation (PsAF). This study investigated the impact of LA linear ablation on the complex-fractionated atrial electrograms (CFAEs) of PsAF patients. METHODS AND RESULTS A total of 40 consecutive PsAF patients (age: 54 ± 10 years, 39 males) who underwent catheter ablation were enrolled in this study. Linear ablation of both roofline between the right and left superior PVs and the mitral isthmus line joining from the mitral annulus to the left inferior PV were performed following PV isolation during AF. High-density automated CFAE mapping was performed using the NAVX, and maps were obtained 3 times during the procedure (prior to ablation, after PV isolation, and after linear ablations) and were compared. PsAF was terminated by ablation in 13 of 40 patients. The mean total LA surface area and baseline CFAEs area were 120.8 ± 23.6 and 88.0 ± 23.5 cm(2) (74.2%), respectively. After PV isolation and linear ablations in the LA, the area of CFAEs area was reduced to 71.6 ± 22.6 cm(2) (58.7%) (P < 0.001) and 44.9 ± 23.0 cm(2) (39.2%) (P < 0.001), respectively. The LA linear ablations resulted in a significant reduction of the CFAEs area percentage in the region remote from ablation sites (from 56.3 ± 20.6 cm(2) (59.6%) to 40.4 ± 16.5 cm(2) (42.9%), P < 0.0001). CONCLUSION Both PV isolation and LA linear ablations diminished the CFAEs in PsAF patients, suggesting substrate modification by PV and linear ablations. (J Cardiovasc Electrophysiol, Vol. 23, pp. 962-970, September 2012).