Hôpital Cardiologique du Haut-Lévêque, and Université Victor Segalen Bordeaux 2, Bordeaux, France
Received 27 October 2004; revised 21 December 2004; accepted 20 January 2005; online publish-ahead-of-print 1 March 2005.
* Corresponding author. Tel: +33 557 65 64 71; fax: +33 557 65 65 09. E-mail address: prash.sanders{at}heartrhythm.org
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Abstract |
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Methods and results Seventy-two patients undergoing catheter ablation of symptomatic drug refractory AF were prospectively randomized to ablation with (n=35; study group) or without (n=37; control group) non-fluoroscopic navigation. PV isolation was performed in all patients. In patients with persistent or inducible sustained AF after PV isolation linear ablation was performed by joining the superior PVs. PV isolation was achieved in all patients; fluoroscopy (15.4±3.4 vs. 21.3±6.4 min; P<0.001) and procedural (52±12 vs. 61±17 min; P=0.02) durations were significantly reduced in the study group. Linear block was achieved in 37 of the 39 patients; with a significant reduction in fluoroscopy (5.6±2.2 vs. 9.9±4.8 min; P=0.003) and procedural (14.7±5.5 vs. 26.6±16.9 min; P=0.007) durations in the study group. After a follow-up of 6.9±2.9 months (range 310), 26 (74%) patients in the non-fluoroscopic navigation group and 29 (78%) patients in the control group were arrhythmia-free after the first procedure.
Conclusion This prospectively randomized study demonstrates significant reduction of fluoroscopy exposure and procedural duration using supplementary non-fluoroscopic imaging system for AF ablation.
Key Words: Atrial fibrillation Pulmonary vein isolation Linear ablation Non-fluoroscopic imaging
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Introduction |
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In parallel with the evolution of these techniques have been the technological innovations to assist with these procedures,913 most requiring proprietary equipment and thus resulting in an increased procedural cost. Recently, a novel non-fluoroscopic imaging system has become commercially available, which combines the rapid generation of 3D cardiac geometry with real-time visualization of any standard electrophysiology catheter to assist ablation.
In this prospective randomized clinical study, we evaluate the effectiveness of EnSite NavX navigation (Endocardial Solutions, St Paul, MN, USA) in facilitating PV electrical isolation and linear substrate modification in patients with AF.
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Methods |
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Electrophysiologic study
Electrophysiological study was performed in the post-absorptive state with sedation. All antiarrhythmic drugs, including calcium channel and beta-blockers, with the exception of amiodarone were ceased five or more half-lives prior to ablation.
Surface electrocardiogram and bipolar endocardial electrograms were continuously monitored and recorded for off-line analysis (Bard EP Division, Lowell, MA, USA). Intracardiac electrograms were filtered from 30 to 500 Hz and measured at a sweep speed of 100 mm/s.
Non-fluoroscopic mapping and navigation
The EnSite NavX system is built on a previously validated platform.14 It utilizes three pairs of nominally orthogonal patches that are driven in time multiplex, with currents of 350 µA at a frequency of 5.7 kHz; the magnitude of the resulting electrical potential shows a linear decrease along its axis and allows exact electrode localization in relation to a reference; in this study, the proximal coronary sinus catheter electrode. The system allows the real-time visualization of the positions of up to 64 electrodes on standard electrophysiology catheters.
In addition, a 3D geometry of the chamber of interest can be created. The system automatically acquires points from a nominated electrode(s) at a rate of 96 points per second. The algorithm defines the surface by using the most distant points in any given angle from the geometry centre, which can be chosen by the operator or is defined by the system. In addition, the operator is able to specify fixed points that represent contact points during geometry acquisition; these points cannot be eliminated by the algorithm that calculates the surface.
To control for variations related to the cardiac cycle, acquisition can be gated to any electrogram. In this study, acquisition of all geometries was gated to ventricular end-diastole and the medium resolution algorithm was used (software version 4.1 and 4.2). Contact points were acquired at the PV ostium using the circumferential mapping catheter (five points per ostium), at the base and the tip of the left atrial appendage (three to five points), at the roof (two points), and at the posterior and inferior left atrium (three to five points).
The repeatability error of the geometry has been previously assessed in an in vitro study and animal study performed for FDA regulatory clearance. The maximum observed distance between two measurements in the in vitro study was 0.24 mm; the upper 95% confidence interval for repeatability being 0.3 mm. In the animal study, a mean distance of 0.7±1.5 mm was observed.
After creation of the geometry, anatomic landmarks (such as the PVs or mitral annulus) can be tagged and marked for guidance. Additional tagging of sites of interest and ablation points can be done during the procedure.
Ablation of AF
All patients had effective anticoagulation for 1 month and transoesophageal echocardiography to exclude left atrial thrombus prior to ablation.
RF ablation was performed with continuous temperature feedback control using a 4 mm tip thermocouple equipped irrigated-tip ablation catheter (Celsius Thermocool; Biosense Webster Europe, Waterloo, Belgium). PV ablation was performed with a target temperature of 50°C, a power limit of 2535 W, and a irrigation of 1020 mL/min. For linear ablation, the target temperature was 50°C, the power limit 3540 W, and the irrigation rate 1060 mL/min. Irrigation rate was titrated to achieve desired power.
Electrical isolation of PV
The techniques used for PV isolation have been described previously.1,8 In brief, the following catheters were introduced via the right femoral vein for electrophysiological study: (i) a steerable quadripolar catheter (Xtrem; Ela Medical, Le Plessis-Robinson, France) was positioned in the coronary sinus; (ii) a circumferential mapping catheter (Lasso; Biosense Webster) was introduced following transseptal access and stabilized with the aid of a long sheath (Preface multipurpose; Biosense Webster) that was continuously perfused with heparinized glucose; and (iii) a 4 mm irrigated-tip ablation catheter (Celsius Thermocool; Biosense Webster).
Following transseptal access, a single bolus of 50 IU/kg body weight of heparin was administered and repeated only for procedures lasting 4 h. Selective PV angiography was performed before and after ablation by hand injection of 510 mL of contrast via an NIH catheter (Cordis Corporation, Miami Lakes, FL, USA).
PV ablation was performed 1 cm from the ostium, which was defined on the basis of angiography. Ablation around the right PVs and on the superior, inferior, and posterior aspect of the left PVs was performed irrespective of the signals on the circumferential catheter. To achieve PV isolation, remaining breakthroughs were mapped with the circumferential catheter and additional ablation performed to isolate the vein. When ablation was required at the anterior portions of the left PVs, energy had to be delivered by infringing the first part of these PVs to achieve catheter stability. The isolation of all PVs was systematically performed in each patient without attempt to first demonstrate their arrhythmogenicity. The procedural endpoint was the elimination or dissociation of the PV potentials as determined by circumferential mapping.
Left atrial linear ablation
Linear ablation was undertaken if patients had persistent or inducible sustained AF after PV isolation. Inducibility was tested as previously described, by burst pacing from the coronary sinus (CS), the left and right atrial appendage; each site was stimulated three times at 20 mA until local AF was induced (burst down to cycle length 150200 ms). Patients were considered inducible when AF lasted for >10 min.8 In this cohort of patients, linear ablation consisted of ablation of the left atrial roof joining the left superior to the right superior PV. The ablation catheter was introduced through the long sheath for stability and ablation started at the left superior PV. Using a dragging technique, ablation was continued to the right superior PV. Special attention was paid to achieve catheter stability in the superior rather than the posterior aspect of the left atrial roof. During dragging, ablation was performed for 6090 s at each point. If mapping indicated persistent gaps, further applications were performed at these sites. The end point of linear ablation was the demonstration of complete linear block defined as the presence of continuous wide double potentials along the ablation line separated by an isoelectric interval during pacing from the left atrial appendage.
Study protocol
For the study protocol, patients were prospectively randomized on a 1 : 1 basis to ablation utilizing (i) fluoroscopic guidance or (ii) additional non-fluoroscopic navigation. In patients randomized to non-fluoroscopic navigation, the procedure began by creation of the left atrial geometry. Geometry creation was performed using either the circumferential mapping catheter (for PVs) or the ablation catheter (body of the left atrium). Fixed anatomical points were acquired circumferentially at the ostia of the PVs, at the mitral annulus, and at the base of the left atrial appendage. The remaining atrial geometry was created automatically during dragging of the catheter utilizing the system's geometry creation function. Ablation was then performed as indicated earlier.
The following parameters were determined: (i) fluoroscopy duration for geometry creation; (ii) procedural duration for geometry creation; (iii) fluoroscopy duration for PV electrical isolation; (iv) procedural duration for PV electrical isolation; and (v) RF energy delivery duration for PV isolation. In patients undergoing left atrial linear ablation, the following parameters were determined: (i) fluoroscopy duration for roofline ablation; (ii) procedural duration for roofline ablation; and (iii) RF energy delivery duration for roofline ablation.
For PV isolation, we started recording procedural time and fluoroscopy exposure after transseptal puncture and positioning of the catheters at the first vein to be ablated and stopped recording the time when disconnection of all veins was achieved. Fluoroscopy and procedural durations required for geometry creation were added to the data for PV isolation in those patients undergoing ablation utilizing non-fluoroscopic navigation. Procedural duration and fluoroscopy exposure for roofline ablation were recorded from the first RF energy application applied to the roofline to documentation of conduction block. When cardioversion was required for documentation of conduction block, owing to ongoing AF, recording was stopped. If further ablation was required, durations were added.
In patients randomized to additional non-fluoroscopic navigation, the operator utilized the navigation system where possible for ablation and catheter movements. Conventional fluoroscopy was available for use at the operator's discretion.
The primary endpoints were fluoroscopy exposure and procedure duration; secondary endpoints were procedural safety and clinical outcome (presence or absence of AF).
Follow up
Following ablation, patients received subcutaneous heparin while oral anticoagulation was re-initiated. In the absence of concurrent indications, all antiarrhythmic drugs were ceased following ablation.
Patients were hospitalized for 1 day at 1, 3, and 6 months after the last procedure for assessment involving transthoracic echocardiography, ambulatory ECG monitoring (48 h), and stress testing. A final follow up is scheduled at 12 months; this follow up includes routine CT scanning of the PVs to exclude PV stenosis.
Patients were considered to have failed ablation if any symptoms of AF recurred and/or if any atrial arrhythmia (AF, atrial tachycardia, or atrial flutter) was documented throughout the follow-up period.
Statistical analysis
The number of patients was prospectively determined to find a 30% reduction of fluoroscopy duration for PV isolation with a power of 80% based on previously published data.13 Variables are expressed as group mean±standard deviation (SD), except number of antiarrhythmic drugs, which is expressed as median and IQR. Continuous variables were compared using the Student's t-test or MannWhitney U test, as appropriate. Categorical variables were compared using the 2 test. Arrhythmia-free survival was compared by KaplanMeier analysis and the log-rank test. Statistical significance was established at two-sided P<0.05.
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Results |
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The procedural parameters for PV isolation are summarized in Table 2. PV isolation using non-fluoroscopic guidance was achieved using 11.2±3.0 min fluoroscopy and took 44±11 min to perform. When the times to create the geometry and the times to isolate the PVs were summed, a significant reduction with the use of non-fluoroscopic navigation was observed when compared with the control group; fluoroscopy time was 15.4±3.4 vs. 21.3±6.4 min (P<0.001) and procedural durations were 52±12 vs. 61±17 min (P=0.02). Fluoroscopy in the non-fluoroscopic guidance group was primarily used to move the circumferential mapping catheter to the targeted PV. During RF energy delivery, assessment of catheter stability and dragging around the ostium was performed without the use of fluoroscopy (Figure 2).
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Left atrial linear ablation
Eighteen of 35 patients (51%) undergoing ablation utilizing non-fluoroscopic navigation and 21 of 37 patients (57%) in the control group had additional linear ablation of the left atrial roof. These patients were matched in both groups for baseline characteristics.
Creation of the roofline was achieved with significantly shorter fluoroscopy (5.6±2.2 vs. 9.9±4.8 min; P=0.003) and procedure time (14.7±5.5 vs. 26.6±16.9 min; P=0.007) using non-fluoroscopic navigation when compared with fluoroscopic guidance alone. There was no significant difference in RF energy delivery (10.2±4.5 vs. 12.8±5.9 min; P=0.177). In all but two patients (one in each group) linear ablation along the roof was demonstrated to have produced conduction block. Conduction block during pacing of the left atrial appendage was associated with a stimulus to potential delay of 154±40 ms (range 105224 ms). In the two patients where conduction block could not be achieved despite 21.6 and 25.0 min of RF energy delivery, conduction delay was 68 and 54 ms, respectively.
Learning curve
To assess the impact of the learning curve on fluoroscopic exposure and procedural duration, we compared procedural parameters for the first and last 10 patients in the study group regarding creation of 3D anatomy and PV isolation. There were no significant differences between the two groups (fluoroscopy anatomy: 4.1 vs. 3.5 min; P=0.4; procedure duration anatomy: 8.1 vs. 7.7 min; P=0.9; fluoroscopy PV isolation: 14.4 vs. 16.9 min; P=0.3; procedure duration PV isolation: 50 vs. 54 min; P=0.2).
Clinical outcome
After a follow-up of 6.2±2.0 months in the control group, and 7.2±2.7 months in the study group, 26 (74%) patients treated with supplementary non-fluoroscopic navigation and 29 (78%) patients in the control group were arrhythmia-free after the first procedure (log-rank test for comparison of the two groups P=0.87; Figure 3). These results include the use of antiarrhythmic drugs (seven patients in each group). Seventeen (24%) of the patients underwent an additional procedure; two patients required two additional procedures. All additional procedures were performed without the use of non-fluoroscopic imaging. The nine recurrence cases in the study group were due to AF (six), left atrial flutter (one), and focal tachycardia (two); the eight recurrence cases in the control group were due to AF (five) and left atrial flutter (three). Overall, 57 (79%) patients were arrhythmia-free without the use of antiarrhythmic drugs after an average of 1.24 procedures, increasing to 65 (90%) with the use of antiarrhythmic drugs.
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Discussion |
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The observed reduction in fluoroscopy exposure attained was 50% during PV isolation and linear ablation. Indeed, the non-fluoroscopic navigation system allows real-time assessment of wall contact and catheter stability as well as assessment of the anatomical position and the relation between the ablation catheter and the circumferential mapping catheter (Figure 2). Owing to these capabilities, catheter displacement and insufficient wall contact are readily recognized without the use of fluoroscopy, resulting in reduction of radiation exposure, procedure duration, and the trend to reduced RF energy delivery. In addition, the feature of acquiring fixed anatomical points allows identification of the narrow ridge between the left PVs and the left atrial appendage (Figure 1), assisting in the positioning of the ablation catheter in the anterior aspect of the left PVs to avoid ablation within the appendage. The advantage is also observed when patients require additional substrate ablation, as geometry creation is required only at the start and can be used throughout the intervention.
Recent evidence suggests that success rates for curative ablation procedures of AF improve with additional left atrial linear lesions.6,7,15 The non-fluoroscopic navigation system allows the creation of linear lesions by tagging ablated areas, which then facilitates the anatomic visualization of the remaining gaps, where additional RF applications can be delivered adjacent to the marked spots (Figure 4) to avoid incomplete lines that are potentially pro-arrhythmic.1618 Among the potential complications of AF ablation, PV stenosis has been attributed to inadvertent distal dislocation of the catheter, particularly in small-diameter PVs. Although we did not observe PV stenosis acutely in either group in this study (assessed by selective PV angiography before and after ablation), continuous real-time monitoring of the catheter position may help further to prevent inadvertent ablation into the PVs.
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Conclusion |
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Acknowledgements |
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Conflict of interest |
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Footnotes |
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References |
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