Radiofrequency Time Research Articles

270 Short-term results of pulmonary vein isolation for paroxysmal atrial fibrillation using duty-cycled bipolar and unipolar radiofrequency energy: The initial Québec experience

BackgroundElectrical isolation of pulmonary veins (PV) is key to long term success of paroxysmal atrial fibrillation (AF) ablation. PV antral isolation using a conventional irrigated-tip catheter is often technically challenging and time consuming.MethodsTwenty-nine patients (mean age 55+/−13 years, 69% males) with symptomatic paroxysmal AF refractory to antiarrhythmic drugs underwent ablation with a circular mapping/ablation decapolar catheter (PVAC). Ablation was performed in the antral region of PVs with a power-modulated bipolar/unipolar radiofrequency (RF) generator using 8W delivered simultaneously through 2-10 electrodes, as selected by the operator. All ablations were performed under general anesthesia.ResultsMean left ventricular ejection fraction was 60+/−4% and mean left atrial volume was 27+/−5 ml/m2. Overall, 114 of 116 targeted PVs (98%) were isolated with the PVAC system with a mean of 32+/−8 RF applications per patient (total RF time 1921+/−493 seconds): 9+/−3 in the right superior PV, 7+/−3 in the right inferior PV, 9+/−4 in the left superior PV, and 7+/−3 in the left inferior PV. The mean procedure and fluoroscopy times were 171+/−35 min and 34+/−12 min respectively. The mean activated clotting time was 335+/−27 sec. After a mean follow-up of 3.6+/−1.7 months, 21 patients (72%) were free of AF without antiarrhythmic drugs . No procedure-related complications were observed.ConclusionPV isolation can be performed effectively, timely and safely using a circular decapolar ablation catheter. Long term and randomized data are needed to compare all different tools and ablation strategies for AF. BackgroundElectrical isolation of pulmonary veins (PV) is key to long term success of paroxysmal atrial fibrillation (AF) ablation. PV antral isolation using a conventional irrigated-tip catheter is often technically challenging and time consuming. Electrical isolation of pulmonary veins (PV) is key to long term success of paroxysmal atrial fibrillation (AF) ablation. PV antral isolation using a conventional irrigated-tip catheter is often technically challenging and time consuming. MethodsTwenty-nine patients (mean age 55+/−13 years, 69% males) with symptomatic paroxysmal AF refractory to antiarrhythmic drugs underwent ablation with a circular mapping/ablation decapolar catheter (PVAC). Ablation was performed in the antral region of PVs with a power-modulated bipolar/unipolar radiofrequency (RF) generator using 8W delivered simultaneously through 2-10 electrodes, as selected by the operator. All ablations were performed under general anesthesia. Twenty-nine patients (mean age 55+/−13 years, 69% males) with symptomatic paroxysmal AF refractory to antiarrhythmic drugs underwent ablation with a circular mapping/ablation decapolar catheter (PVAC). Ablation was performed in the antral region of PVs with a power-modulated bipolar/unipolar radiofrequency (RF) generator using 8W delivered simultaneously through 2-10 electrodes, as selected by the operator. All ablations were performed under general anesthesia. ResultsMean left ventricular ejection fraction was 60+/−4% and mean left atrial volume was 27+/−5 ml/m2. Overall, 114 of 116 targeted PVs (98%) were isolated with the PVAC system with a mean of 32+/−8 RF applications per patient (total RF time 1921+/−493 seconds): 9+/−3 in the right superior PV, 7+/−3 in the right inferior PV, 9+/−4 in the left superior PV, and 7+/−3 in the left inferior PV. The mean procedure and fluoroscopy times were 171+/−35 min and 34+/−12 min respectively. The mean activated clotting time was 335+/−27 sec. After a mean follow-up of 3.6+/−1.7 months, 21 patients (72%) were free of AF without antiarrhythmic drugs . No procedure-related complications were observed. Mean left ventricular ejection fraction was 60+/−4% and mean left atrial volume was 27+/−5 ml/m2. Overall, 114 of 116 targeted PVs (98%) were isolated with the PVAC system with a mean of 32+/−8 RF applications per patient (total RF time 1921+/−493 seconds): 9+/−3 in the right superior PV, 7+/−3 in the right inferior PV, 9+/−4 in the left superior PV, and 7+/−3 in the left inferior PV. The mean procedure and fluoroscopy times were 171+/−35 min and 34+/−12 min respectively. The mean activated clotting time was 335+/−27 sec. After a mean follow-up of 3.6+/−1.7 months, 21 patients (72%) were free of AF without antiarrhythmic drugs . No procedure-related complications were observed. ConclusionPV isolation can be performed effectively, timely and safely using a circular decapolar ablation catheter. Long term and randomized data are needed to compare all different tools and ablation strategies for AF. PV isolation can be performed effectively, timely and safely using a circular decapolar ablation catheter. Long term and randomized data are needed to compare all different tools and ablation strategies for AF.

Robotic catheter ablation of left ventricular tachycardia: initial experience

Catheter ablation of ventricular tachycardia (VT) can be technically challenging due to difficulty with catheter positioning in the left ventricle (LV) and achieving stable contact. The Hansen Sensei Robotic system (HRS) has been used in atrial fibrillation but its utility in VT is unclear. The purpose of this study was to test the technical feasibility of robotic catheter ablation of LV ventricular tachycardia (VT) using the HRS. Twenty-three patients underwent LV VT mapping and ablation with the HRS via a transseptal, transmitral valve approach. Nineteen patients underwent substrate mapping and ablation (18 had ischemic cardiomyopathy, 1 had an apical variant of hypertrophic cardiomyopathy). Four patients had focal VT requiring LV VT mapping and ablation. Procedural endpoints included substrate modification by endocardial scar border ablation and elimination of late potentials, or elimination of inducible focal VT. Mapping and ablation were entirely robotic without requiring manual catheter manipulation in all patients and reaching all LV regions with stable contact. Fluoroscopy time of the LV procedure was 22.2 ± 11.2 minutes. Radiofrequency time was 33 ± 21 minutes. Total procedural times were 231 ± 76 minutes. Complications included a left groin hematoma (opposite to the HRS sheath), 1 pericardial effusion without tamponade that was drained successfully, and transient right ventricular failure in a patient with previous left ventricular assist device. At 13.4 ± 6.7 months of follow-up (range 1-19 months), recurrence of VT occurred in 3 of 23 patients. Our initial experience suggests that the HRS allows successful mapping and ablation of LV VT.

Tissue typing using ultrasound RF time series: Experiments with animal tissue samples

This article provides experimental evidence to show that the time series of radiofrequency (RF) ultrasound data can be used for tissue typing. It also explores the tissue typing information in RF time series. Clinical and high-frequency ultrasound are studied. Bovine liver, pig liver, bovine muscle, and chicken breast were used in the experiments as the animal tissue types. In the proposed approach, the authors record RF echo signals backscattered from tissue, while the imaging probe and the tissue are stationary. This sequence of recorded RF data generates a time series of RF echoes for each spatial sample of the RF signal. The authors use spectral and fractal features of ultrasound RF time series averaged over a region of interest, along with feedforward neural networks for tissue typing. The experiments are repeated at ultrasound frequency of 6.6 and also 55 MHz. The effects of increasing power and frame rate are studied. The methodology yielded an average two-class classification accuracy of 95.1% when ultrasound data were acquired at 6.6 MHz and 98.1% when data were collected with a high-frequency probe operating at 55 MHz. In four-class classification experiments, the recorded accuracies were 78.6% and 86.5% for low and high-frequency ultrasound data, respectively. A set of 12 texture features extracted from the B-mode image equivalents of the RF data yields an accuracy of only 77.5% in typing the analyzed tissues. An increase in acoustic power and the frame rate of ultrasound results in an improvement in classification results. The results of this study demonstrate that RF time series can be used for ultrasound-based tissue typing. Further investigation of the underlying physical mechanisms is necessary.

Endo-epicardial ablation of ventricular arrhythmias in the left ventricle with the Remote Magnetic Navigation System and the 3.5-mm open irrigated magnetic catheter: Results from a large single-center case–control series

Remote magnetic navigation (RMN) has been reported as a feasible and safe mapping and ablation system for treatment of ventricular arrhythmias (VAs). However, the reported success rates have been limited with the 4- and 8-mm catheter tips. This study sought to report the results in a large series of consecutive patients undergoing radiofrequency (RF) catheter ablation of VAs using the RMN with the 3.5-mm magnetic open-irrigated-tip catheter (OIC). A total of 110 consecutive patients with a clinical history of left VA were included in the study. In all cases, an OIC was utilized for mapping and ablation. When ablation with the RMN catheters failed, a manual OIC was used to eliminate the VA. Postablation pacing maneuvers and isoproterenol were used to verify the inducibility of the VAs. Outcomes were compared with those of a group of 92 consecutive patients undergoing manual ablation by the same operator. Mapping and ablation with the magnetic OIC were performed in all 110 patients with VA. Ischemic cardiomyopathy was present in 33 (30%), nonischemic in 14 (13%), and in 63 (57%) patients no structural heart disease was present. Endocardial mapping was performed in all patients, whereas both endocardial and epicardial mapping were performed in 36 (33%) patients. Compared with manual ablation, RMN was associated with a longer procedural time (2.9 +/- 1.2 hours vs. 3.3 +/- 1.1 hours, P = 0.004) and RF time (24 +/- 12 minutes vs. 33 +/- 18 minutes, P = 0.005), whereas fluoroscopic time was significantly shorter (35 +/- 22 minutes vs. 26 +/- 14 minutes, P = 0.033). During the procedures, crossover to manual ablation was required in 15 patients (14%). At 11.7 +/- 2.1 months of follow-up in the study group and 18.7 +/- 3.7 months in the manual ablation group, 85% and 86% (P = 0.817) of patients, respectively, were free of VA. This large series of consecutive patients demonstrates that OIC ablation using RMN is effective for the treatment of left VAs.

SSFP signal with finite RF pulses

The theoretical description of steady state free precession (SSFP) sequences is generally well accepted and unquestioned, although it is based on instantaneously acting radiofrequency (RF) pulses. In practice, however, all excitation processes are finite, thereby questioning the overall validity of the common SSFP signal description for use with finite RF pulses. In this paper, finite RF pulse effects on balanced SSFP signal formation are analyzed as a function of the RF time, the pulse repetition time, the flip angle (alpha) and relaxation times (T(1,2)). The observed signal modulations from finite RF pulses (compared to infinitesimal ones) can range from only a few percent (for RF time/pulse repetition time << 1, alpha << 90 degrees, T(2)/T(1) approximately 1) to over 10% (for RF time/pulse repetition time << 1, alpha approximately 90 degrees, T(2)/T(1) << 1) and may even exceed 100% in the limit of RF time/pulse repetition time --> 1 (for alpha approximately 90 degrees, T(2)/T(1) << 1). As a result, a revision of SSFP signal theory is indicated not only for reasons of completeness but also seems advisable, e.g., for all quantitative SSFP methods. A simple modification for the common balanced SSFP equation is derived that provides an accurate framework for SSFP signal description over a wide variety of practical and physiologic parameters.

Safety and feasibility of catheter ablation for atrioventricular nodal re-entrant tachycardia without fluoroscopic guidance

Nonfluoroscopic intracardiac navigation systems reduce the dose of radiation in most ablation procedures. However, they have not been sufficiently studied as a sole guidance tool for electrode catheter handling. The purpose of our study was to assess the feasibility and safety of catheter ablation for atrioventricular nodal re-entrant tachycardia (AVNRT) without the use of fluoroscopy. We prospectively enrolled all of the patients with AVNRT (Group A) treated by catheter ablation guided only by a nonfluoroscopic intracardiac navigation system. These patients were compared with a matched control group of patients (Group B) who had undergone an ablation procedure for AVNRT guided only by fluoroscopy in the preceding months. We compared the success rate and the rate of complications and recurrences. We also compared the procedure and radiofrequency times. Fifty patients were enrolled in each group. The procedure was successful in 100% in Group A versus 96% in Group B (P = .15). One patient in Group A and 4 patients in Group B suffered nonserious complications (P = NS). The mean fluoroscopy time in Group B was 18 +/- 16 min (range 3.5 to 77, total 924). In 1 case in Group A (2%), the use of fluoroscopy was required. Procedure and radiofrequency times did not differ between the 2 groups. A recurrence developed in 2 patients in each group (P = NS). Catheter ablation for AVNRT without fluoroscopic guidance is feasible and safe, and does not prolong procedure time. The reduction in radiation dose is considerable for patients and professionals.

Combined Cementoplasty and Radiofrequency Ablation in the Treatment of Painful Neoplastic Lesions of Bone

To assess the safety and effectiveness of combined radiofrequency (RF) ablation and cementoplasty in the treatment of painful neoplastic lesions of bone. The authors performed a retrospective analysis of 25 combined treatments comprising RF ablation followed by injection of polymethylmethacrylate cement performed in 19 patients during a 22-month period. Patients ranged in age from 42 to 82 years (mean, 58.9 years) and included five women and 14 men. Eleven vertebrae (eight lumbar and three thoracic), nine acetabulae, three sacra, one pubis, and one humerus were treated with a total of 36 RF ablations (in several instances, overlapping ablations were used). The location of the primary neoplasm, lesion size, pain before and after the procedure (as determined with a 10-point visual analog scale [VAS]), number of RF treatments, type of device used for cementoplasty, RF time, cement volume, and extravasation were documented. A total of 25 combined RF ablations and cementoplasties were performed. The technical success rate was 100% (25 of 25 treatments). There were seven minor complications: six limited cement extravasations and a transient thermal nerve injury. The mean RF time was 9.1 minutes (range, 6-12 minutes). The mean cement volume injected was 6.1 mL (range, 0.8-16 mL). The mean preprocedure pain (as measured with a VAS) was 7.9 (range, 7.0-9.0) and the mean posttreatment pain was 4.2 (range, 0-6); the difference was statistically significant (mean score, 4.08; 95% confidence interval: 3.92, 4.87; P < .0001) using a paired t test. Combined RF ablation and cementoplasty appears to be safe and effective in the treatment of painful neoplastic lesions of bone.

Color-coded three-dimensional entrainment mapping for analysis and treatment of atrial macroreentrant tachycardia

Mapping and ablation of atrial macroreentrant tachycardia focus on activation mapping with identification of the area of slow conduction. The purpose of this study was to evaluate a new concept for analysis and treatment of macroreentrant tachycardia based on color-coded three-dimensional (3D) entrainment mapping and subsequent placement of strategic lesion lines. Twenty-six patients presented with macroreentrant tachycardia (cycle length 329 +/- 70 ms). Using nonfluoroscopic systems (CARTO 12, NavX 14), sequential mapping of the target atrium was performed. On each mapping point, the 3D location was paired with color-coded entrainment information so that the reentrant circuit could be directly visualized. Procedural duration, fluoroscopy time, and radiofrequency time measured 181 +/- 58, 37 +/- 19, and 31 +/- 17 minutes, respectively. Thirty-nine macroreentrant tachycardias were ablated: perimitral 9, around pulmonary vein ostium 6, through left atrial roof 5, around left atrial appendage 3, right atrial cavotricuspid isthmus dependent 6, around right atrial scar 2, around superior vena cava 1, within the septum 5, and within the coronary sinus 2. Tachycardia termination and noninducibility of any macroreentrant tachycardia was the procedural end-point. In case of left atrial macroreentrant tachycardia, pulmonary vein isolation was completed. Follow-up with serial 7-day Holter covered 302 +/- 82 days. Two (8%) patients experienced recurrences of a pretreated macroreentrant tachycardia. In patients with macroreentrant tachycardia, color-coded 3D entrainment mapping is feasible to accurately determine and visualize the 3D location of the reentrant circuit and to plan a strategic ablation line concept. That approach, not targeting the area of slow conduction of the circuit, resulted in excellent procedural success (100%), with long-term freedom from any tachycardia recurrences in 88% of patients.

Cardiac injury after percutaneous catheter ablation for atrial fibrillation

Small elevations in troponin T levels have been shown with limited radiofrequency (RF) ablation procedures for supraventricular tachycardia, usually to levels below the threshold for ischaemia or infarction. Left atrial catheter ablation for atrial fibrillation (AF) requires far more RF energy, therefore could be expected to have greater elevation in troponin T. We determined troponin T levels before and after ablation in these patients to evaluate the amount of rise with this ablation. All patients undergoing pulmonary vein isolation (PVI) from May 2004 to October 2004 had troponin T levels measured 4 h following completion of the procedure. The first 30 patients also had a troponin T level measured 1 h prior to PVI to establish a baseline reference. Sixty patients were studied, with 81.7% males and a mean age of 54.6 +/- 9.9 years. No patient had underlying structural heart disease. The baseline troponin T level was normal (<0.01 microg/L) in all 30 patients. Post-procedure troponin T levels were elevated in all 60 patients compared with baseline (P < 0.05), with a mean level of 0.85 microg/L and a range of 0.26-1.57 microg/L after an average RF ablation time of 56 +/- 15 min. All levels were above the reference range for diagnosis of acute myocardial infarction (>0.15 microg/L). Troponin T level was not related to the number of RF lesions, RF time, procedure time, or associated external cardioversion. Troponin T elevations occurred in all patients undergoing PVI, to levels at least 20 times the normal concentration, into the range for diagnosis of acute myocardial infarction. Therefore, troponin T would not be specific for ischaemia in the setting of chest pain post-catheter ablation for AF.

Radiofrequency ablation of atypical atrial flutter after cardiac surgery or atrial fibrillation ablation: A randomized comparison of open-irrigation-tip and 8-mm-tip catheters

The efficacy of radiofrequency ablation of atypical atrial flutter (AAFL) remains relatively low. This is probably related to the complex mechanism of this arrhythmia or may be due to an inability to deliver sufficient energy during ablation. The aim of this study is to assess whether an open-irrigation-tip catheter or an 8-mm-tip catheter is more effective for ablation of AAFL in patients with prior history of cardiac surgery and/or catheter ablation of atrial fibrillation. Seventy patients with AAFL after cardiac surgery/atrial fibrillation ablation were randomized for ablation with either an open-irrigation-tip catheter (Group 1, n=36) or an 8-mm-tip catheter (Group 2, n=34). Acute success was defined as the termination of AAFL by radiofrequency delivery and noninducibility by programmed pacing at the end of procedure. Patients' postoperative courses were followed up by means of intermittent standard electrocardiogram (ECG), transtelephonic ECG monitoring, and telephone interview. All patients underwent 48-hour Holter monitoring at their 3-, 6-, and 9-month follow-up after ablation. Acute success was achieved in 34 patients (94.4%) in Group 1 and 26 patients (76.5%) in Group 2 (P<.05). As compared with the patients in Group 2, more patients in Group 1 remained in sinus rhythm without antiarrhythmic drugs at 90-day follow-up (22 vs 8, P<.05). After 10 months of follow-up, 91.7% of the patients from Group 1 were free of atrial tachyarrhythmias, whereas only 58.9% of the patients from Group 2 remained in sinus rhythm (P <.05). The fluoroscopy and radiofrequency times were significantly shorter when an open-irrigation-tip ablation catheter was used. In patients with a prior history of cardiac surgery or ablation for atrial fibrillation, an open-irrigation-tip catheter is superior to an 8-mm-tip catheter for radiofrequency ablation of scar-related AAFLs. Patients ablated with an open-irrigation-tip catheter seem to have higher acute success rate with less x-ray exposure and radiofrequency delivery, and have a more favorable long-term outcome with more patients maintaining sinus rhythm without antiarrhythmic drugs.

Elimination of cavotricuspid isthmus conduction by a single ablation lesion: observations from a maximum voltage-guided ablation technique

The architecture of the cavotricuspid isthmus has been shown to be highly variable made of a large number of interspersed bundles in the majority. Targeting high-amplitude signals has resulted in short-ablation times, likely due to the selective ablation of such bundles. We report a series of cases where a single site ablation resulted in bidirectional block, supporting the hypothesis that conduction can occur over a discrete portion of the isthmus. Sixty consecutive patients underwent ablation for isthmus-dependent atrial flutter using voltage-guided approach between September 2005 and June 2006. We found in five patients (8.3%) (four male, mean age 58.1 +/- 11.4 years), in whom bidirectional block was achieved by ablation at a single site. The isthmus was mapped at the 6 o'clock LAO position, and bipolar amplitude was measured during pull-back to find the site of largest atrial voltage. The atrial and ventricular electrogram (EGM) measured 2.00 +/- 1.6 and 0.2 +/- 0.1 mV, respectively, at the successful site, resulting in the mean atrium/ventricle ratio of 9.1 +/- 4.1. The total radiofrequency time was 83.8 +/- 25.3 s, and the procedure time was 68.6 +/- 10.4 min, including 30 min waiting time after the procedure. Flutter has not recurred over 5.7 +/- 4.0 months follow-up. Targeting the largest atrial EGM in the isthmus can produce bidirectional block with a single site ablation. This supports the hypothesis that trans-isthmus conduction can occur over a discrete part of the isthmus, likely due to the underlying bundle architecture.

Sluggish light for radio-frequency true-time-delay applications with a large time-bandwidth product

A new radio-frequency (RF) photonic technique for achieving large RF time delays has been experimentally demonstrated using femtosecond pulses modulated by an acousto-optic tunable filter in a frequency-mapped and Doppler-shifted modulation scheme. A short optical delay line with length of 240 mum produces nearly 3 micros RF time delay after optical heterodyne detection, resulting in an effective slow-light velocity of 86 m/s. A delay-to-pulse-width ratio of 20 based on this technique has been observed, with a larger fractional delay foreseeable.

Radiofrequency Thermal Ablation: Increase in Lesion Diameter with Continuous Acetic Acid Infusion

To evaluate the influence of continuous infusion of acetic acid 50% during radiofrequency ablation (RFA) on the size of the thermal lesion produced. Radiofrequency (RF) was applied to excised bovine liver by using an expandable needle electrode with 10 retractable tines (LeVeen Needle Electrode, RadioTherapeutics, Sunnyvale, CA) connected to a commercially available RF generator (RF 2000, RadioTherapeutics, Sunnyvale, CA). Experiments were performed using three different treatment modalities: RF only (n = 15), RF with continuous saline 0.9% infusion (n = 15), and RF with continuous acetic acid 50% infusion (n = 15). RF duration, power output, tissue impedance, and time to a rapid rise in impedance were recorded. The ablated lesions were evaluated both macroscopically and histologically. The ablated lesions appeared as spherical or ellipsoid, well-demarcated pale areas with a surrounding brown rim with both RF only and RF plus saline 0.9% infusion. In contrast, thermolesions generated with RF in combination with acetic acid 50% infusion were irregular in shape and the central portion was jelly-like. Mean diameter of the coagulation necrosis was 22.3 +/- 2.1 mm (RF only), 29.2 +/- 4.8 mm (RF + saline 0.9%) and 30.7 +/- 5.7 mm (RF + acetic acid 50%), with a significant increase in the RF plus saline 0.9% and RF plus acetic acid 50% groups compared with RF alone. Time to a rapid rise in impedance was significantly prolonged in the RF plus saline 0.9% and RF plus acetic acid 50% groups compared with RF alone. A combination of RF plus acetic acid 50% infusion is able to generate larger thermolesions than RF only or RF combined with saline 0.9% infusion.

New Simplified Technique for 3D Mapping and Ablation of Right Ventricular Outflow Tract Tachycardia

To evaluate the safety and efficacy of using a circular multielectrode catheter for mapping and ablation of ventricular tachycardia (VT) or premature ventricular complexes (PVCs) from the right ventricular outflow tract (RVOT). Three-dimensional (3D) mapping systems are commonly used for mapping and ablation of RVOT VT and PVCs. Newer catheters that are circular with multiple electrodes, such as the Lasso catheter, are capable of simultaneously recording from multiple points within a circumferential plane. Given the tubular structure of the RVOT, these catheters could be used for mapping tachycardias from the RVOT. A retrospective cohort study of patients undergoing radiofrequency (RF) ablation of RVOT VT or PVCs was performed. In group 1 (n = 7), mapping was performed with a single ablation catheter and fluoroscopy. In group 2 (n = 10), 3D mapping using ESI (n = 9) or CARTO (n = 1) was performed. In group 3 (n = 12), mapping was performed with a circular multielectrode catheter (n = 12). All ablations were performed with 4-mm tip catheters using RF energy. Catheter ablation for RVOT VT (n = 15) or PVCs (n = 14) was performed on 29 cases in 26 patients, 9 males. Mean age was 35.9 years. In groups 1, 2, and 3, the mean number of lesions was 17.7 +/- 7.7, 13.6 +/- 7.7, and 18.2 +/- 22.7 and the median number of lesions was 20, 13, and 5, respectively. There were no significant differences in the number of lesions, RF time, fluoroscopy time, procedure time, and acute success rate among the three techniques. There were three complications in group 2 and one in group 3. The use of a circular multielectrode catheter is as effective as the other standard available 3D mapping techniques, both in terms of procedural success and procedural characteristics. Additionally, because of the lower cost associated with using the circular multielectrode catheter approach, further evaluation should be performed to determine whether this is the most cost-effective approach to 3D mapping and ablation of RVOT tachycardias.

Correlation of atrial electrocardiographic amplitude with radiofrequency energy required to ablate cavotricuspid isthmus-dependent atrial flutter

The purpose of this study was to evaluate a possible correlation between atrial ECG amplitude in common atrial flutter (AFL) and radiofrequency (RF) energy required to achieve cavotricuspid isthmus block. The amount of RF delivery required for ablation of typical AFL is variable. This variation has been attributed to the cavotricuspid isthmus anatomy. Atrial ECG amplitude can be a marker of atrial anatomic variations and therefore may correlate with RF duration required to achieve cavotricuspid isthmus block. Seventy consecutive patients were prospectively studied. Ablation of the cavotricuspid isthmus was performed by creating a line of block between the inferior tricuspid annulus and the inferior caval vein using 8-mm-tip electrode catheters. If more than 20 minutes of RF time was required to achieve conduction block, the catheter was changed to an irrigated-tip catheter. Atrial ECG amplitude was assessed in leads II, III, aVF, and aVL. A total of 14 +/- 11 minutes of RF energy was delivered to achieve block in all patients; 12 patients (8%) required more than 20 minutes. Atrial ECG amplitude showed highly significant correlations with cumulative RF energy (F and P waves in lead II: r = 0.703 and r = 0.737, P < .001). P-wave amplitude <0.2 mV and/or flutter wave amplitude <0.35 mV in lead II have a high negative predictive value to predict <20 min RF delivery (96% and 89% respectively). A significant correlation exists between atrial ECG amplitude and amount of RF required to ablate typical AFL. Atrial ECG amplitude may be a surrogate marker of characteristics of isthmus anatomy. These findings may influence the choice of catheter used for cavotricuspid isthmus ablation.

An overview of the information distribution system at the Advanced Photon Source

The Advanced Photon Source (APS) has been in operational mode for more than 5 yr. Currently there are over 40 beamlines in various phases of operation. The control system of choice at the APS is the Experimental Physics and Industrial Control System (EPICS). We have provided various interfaces to the beamlines from the APS control system. An overview of the various systems will be discussed. The General Control System Information (GCSI) uses dedicated computers as EPICS process variable gateways to provide data from the APS control system to each beamline. The GCSI architecture makes the APS control system secure, yet has the flexibility of providing access control to any data available on the APS control system. In addition, the gateway reduces the load on the APS control system equipment by making only one connection for each process variable accessed by multiple users. Each sector, consisting of a bending magnet and insertion device beamlines, is provided its own gateway, which resides on the local sector network. This scheme has the advantage of providing network security and more reliable operation. To provide real-time accelerator data to beamlines, each sector has been provided a chassis to display the storage ring current and other relevant information. These data are transmitted via a direct fiber link from the APS control system hardware to the beamlines. The beamlines are also provided VME-based hardware and associated EPICS software to retrieve key information provided via this fiber link. Some of the information on this link is beam current, lifetime, injection status, and sector specific information such as shutter status, insertion device gap, and energy, and storage ring and front-end beam position monitor signals. The data rates on this link are typically 10 Hz but can be as high as 272 kHz. This scheme allows the beamlines using EPICS-based software to seamlessly use the data from the APS control system without excessively impacting the system. For high-precision x-ray timing experiments, a new scheme has been designed to distribute the radio-frequency timing signals to the beamlines. Using VME-based hardware and EPICS software, the bunch clock signal is generated at the beamline for use in timing experiments. Data are provided at the radio frequency of 352 MHz. Beamlines have also been provided with hardware and software to generate the bunch clock signal for timing experiments.

Dynamic plasma behaviour excited by m=+or-1 helicon wave

The dynamic behaviour of a plasma produced by a helicon wave using exciting m=1 and -1 helical modes is investigated. The RF (radio frequency) power dependence, antenna-plasma coupling, and time evolution of plasma parameters and Ar line intensities are studied in relation to the density jump, i.e. a steep increase in density to a level of 1013 cm-3 by the application of an RP input power greater than 1 kW. Before the density jump, the excited wave is localized near the antenna, exhibiting a standing wave character. After the jump, this wave propagates outwards and a dispersion relation for the helicon wave is confirmed.

Effect of radio-frequency plasma nitriding time on the structure and magnetic properties of 304 austenite stainless steel

Effect of radio-frequency plasma nitriding time on the structure and magnetic properties of 304 austenite stainless steel