Summary
Background
Catheter ablation of atrial fibrillation (AF) focuses on pulmonary vein isolation (PVI), but the procedure is associated with significant X-ray exposure. Few data exist concerning the combination of remote magnetic navigation (RMN) and a new three-dimensional non-fluoroscopic navigation system (Carto ® 3), which facilitates precise catheter navigation and limits X-ray exposure.
Aims
To assess the efficacy and extent of fluoroscopic exposure associated with the combination of RMN and the Carto 3 system in patients requiring AF ablation.
Methods
Between January and September 2011, catheter ablation was performed remotely using the Carto 3 system in 81 consecutive patients who underwent PVI for symptomatic drug-refractory AF. The radiofrequency generator was set to a fixed power ≤ 35 W. The primary endpoint was wide-area circumferential PVI confirmed by spiral catheter recording during ablation and including additional lesion lines (left atrial roof and coronary sinus defragmentation) or complex fractionated atrial electrograms for persistent AF. Secondary endpoints included procedural data, complications and freedom from atrial tachycardia (AT)/AF.
Results
Mean age was 60 ± 9 years; 20% were women; 73% had symptomatic paroxysmal AF; 27% had persistent AF. The CHA 2 DS 2 -VASc score was 1.2 ± 1. Median procedure time was 3.5 ± 1 hours; median total X-ray exposure time was 13 ± 7 minutes; transseptal puncture and catheter positioning took 8 ± 4 minutes, left atrium electroanatomical reconstruction 1 ± 4 minutes and catheter ablation 3.5 ± 5 minutes. Recurrences were AT ( n = 3; 3.7%), paroxysmal AF ( n = 8; 9.9%) and persistent AF ( n = 4; 4.9%); redo ablation was performed in these 15 (19%) patients. After a median follow-up of 15 ± 6 months and a single procedure, 71% of patients were free of symptoms; 84% remained asymptomatic after two procedures.
Conclusions
RMN with irrigated catheters combined with the Carto 3 system can be effectively performed in patients requiring AF ablation with minimal use of fluoroscopy, but larger randomized studies are warranted.
Résumé
Contexte
L’isolation électrique des veines pulmonaires (VP) est la cible principale du traitement par radiofréquence (RF) de la fibrillation atriale (FA), mais ces procédures sont longues et exposent de manière significative aux rayons X (RX). Dans ce contexte, peu de données sont disponibles dans la littérature sur l’utilisation combinée de la navigation par robot magnétique (NRM) et du nouveau système de cartographie 3-D (Carto ® 3 system).
Objectifs
L’objectif de cette étude prospective était d’évaluer l’efficacité et le niveau d’exposition aux RX lors de l’utilisation combinée de la NRM couplée au système Carto 3 au cours de l’ablation de FA.
Méthodes
Entre janvier et septembre 2011, l’utilisation combinée des deux systèmes a été réalisée chez 81 patients consécutivement. Une isolation exclusive des VP était réalisée pour les patients avec FA paroxytique alors que les patients avec FA persistante avaient une isolation circonférentielle des VP couplée à une ligne sur le toit et une défragmentation du sinus coronaire. Les objectifs secondaires étaient basés sur l’évaluation des données des procédures, des complications et des récidives de troubles rythmiques auriculaires.
Résultats
La moyenne d’âge de la population était de 60 ± 9 ans (20 % femmes), avec FA paroxystique (73 %) ou persistante (27 %). Le score de CHA 2 DS 2 -VASc était de 1,2 ± 1. Le temps médian de procédure était de 3,5 ± 1 heures et le temps médian d’exposition aux RX était de 13 ± 7 min; le temps nécessaire au cathétérisme transeptal était de 8 ± 4 min, le temps pour la reconstruction anatomique de 1 ± 4 min, alors que le temps moyen d’ablation était de 3,5 ± 5 min. Trois patients ont récidivé sous la forme de tachycardie atriale (3,7 %), huit en FA paroxystique (9,9 %), et quatre en FA persistante (4,9 %). Après un suivi moyen de 15 ± 6 mois et une seule procédure, 71 % des patients étaient asymptomatiques, alors que 84 % restaient asymptomatiques après deux procédures. Une nouvelle séance de RF a été réalisée chez 15 (19 %) patients.
Conclusions
L’utilisation combinée du robot magnétique au système de cartographie (Carto 3) représente une alternative efficace pour l’ablation de la FA avec une utilisation très faible de rayons X.
Background
Over the past few years, radiofrequency (RF) therapy has had a decisive place in the treatment of complex arrhythmias and, more particularly, atrial fibrillation (AF) . This technology requires experienced operators with special skills in manipulating catheters in difficult clinical situations, so this intervention may involve long, tedious and potentially risky procedures . Catheter technology is a major limitation to the manual method, as catheter mobility is limited by the transmission of the torque, which depends on vessel tortuosity, catheter orientation in the heart and catheter rigidity or instability. During these procedures, the operator is exposed not only to X-rays, but also to abnormal fatigue, which may lead to a loss of concentration. This decreased concentration may result in delayed analysis, a lengthened procedure and an increased risk of complications. AF treatment is increasingly used in electrophysiological laboratories due to the prevalence of AF (2–3% of the population aged > 60 years) and the low benefit/risk ratio of antiarrhythmic drugs compared with RF techniques, as shown in several randomized studies . The current trend favours technology that is similar to or more effective than manual RF techniques, but is safer in terms of potential complications and other variables such as X-ray exposure for patient and operator. Such technology should eventually allow the management of more patients without adverse effects on the operators’ health. The remote magnetic navigation (RMN) system appears to be a futuristic technology benefiting from a very favourable benefit/risk ratio for both the patient and operator . Several other technological innovations facilitating AF ablation have been proposed, but there are few data available concerning the combination of RMN with a new three-dimensional (3D) non-fluoroscopic navigation system (Carto ® 3; Biosense Webster, CA, USA), which facilitates precise catheter navigation and limits X-ray exposure .
This prospective study aimed to evaluate the efficacy and extent of fluoroscopic exposure associated with the combination of RMN and the Carto 3 system in patients requiring AF ablation .
Methods
Catheter ablation was performed remotely using the Niobe II RMN system (Stereotaxis; St. Louis, MO, USA) combined with a new 3D non-fluoroscopic navigation system (Carto 3 system) in 81 consecutive patients who underwent pulmonary vein disconnection for symptomatic drug-refractory AF.
Electrophysiological procedures
All patients received anticoagulation therapy with vitamin K antagonists (VKAs) for at least 2 months prior to the procedure (target international normalized ratio, 2–3). Therapeutic anticoagulation was maintained with intravenous or low-molecular-weight heparin following VKA discontinuation, starting 3 days before the intervention. Transoesophageal echocardiography was performed within 48 hours before the procedure to exclude left atrial thrombus. VKAs were resumed the day after the procedure and effective anticoagulation was maintained with heparin until the international normalized ratio was > 2.0. Surface electrocardiograms and bipolar endocardial electrograms (filtered from 30 to 500 Hz) were continuously monitored and stored on a computer-based digital amplifier/recorder system. A deflectable quadripolar catheter (5 mm interelectrode spacing; Xtrem; ELA Medical, Montrouge, France) was positioned in the coronary sinus for pacing and recording. The left atrium was accessed by a patent foramen ovale, when present, or by transseptal puncture. A guidewire was introduced into the left atrium using an 8F long sheath. The sheath was perfused during the procedure with heparinized solution (3000 U of heparin in 500 mL of sodium chloride 0.9% at a rate of 150 mL/h). A multipolar deflectable catheter (Lasso; Biosense Webster, Diamond Bar, CA, USA) was inserted through the long sheath to map the pulmonary vein ostia for all ablation procedures. RF ablation was performed using a 3.5 mm open irrigated-tip magnetic ablation catheter (NaviStar ® RMT ThermoCool ® ; Biosense Webster, Diamond Bar, CA, USA). The catheter was advanced into the left atrium through a second transseptal puncture. The venous sheath was then withdrawn in the right atrium and continuously perfused. Following transseptal puncture, intravenous unfractionated heparin was administered as a bolus (7500 units); additional boluses were given throughout the procedure to maintain an activated clotting time of ≥ 300 seconds. Activated clotting time was determined 30 minutes after transseptal puncture and every 30 minutes thereafter. When the activate clotting time was < 300 seconds, an additional bolus of 2500 units was administered. Deep sedation was achieved using intravenous nalbuphine and midalzolam.
Radiofrequency catheter ablation procedures
Regardless of the study group, the endpoints of ablation were isolation of the pulmonary veins, defined by complete elimination or dissociation of pulmonary potentials validated with a circumferential mapping catheter in all cases (paroxysmal and persistent AF), and the creation of linear lesions interconnecting the upper pulmonary vein ostia (roof line).
RF was applied using an open irrigated-tip catheter with a power output < [≤?] 35 W close to the pulmonary vein ostia and 30 W for the roofline or while creating coronary sinus disconnection. Irrigation with sodium chloride 0.9% at a rate of 20–35 mL/min was employed to maintain a tip temperature of < 43 °C.
Carto 3 system features
The Carto 3 system allows for real-time Advanced Catheter Location™ and visualization of both ablation and circular mapping catheters (NaviStar and Lasso catheters) ( Fig. 1 ). The catheter location display is identical to that of the fluoroscopic view.
The Carto 3 system combines electromagnetic technology (as in the Carto XP system; Biosense Webster, CA, USA) with new advanced catheter location technology that enables visualization of multiple catheters without fluoroscopy. Briefly, advanced catheter location is an impedance-based catheter localization system that enables precise cardiac mapping and navigation with multiple electrodes. Six electrode patches are attached to the body surface, which constantly monitor the current emitted at a frequency unique to each individual catheter electrode. Each electrode patch is also equipped with a magnetic sensor, enabling 3D localization. Currents detected at the patches relate the electrode’s 3D positioning inside the human body. The Carto 3 system’s ability to visualize manipulation and placement of circular mapping catheters in each vein may further reduce fluoroscopy time. This new system also improves catheter stability during ablation and eases identification of each catheter electrode-pair position. Visualization of catheters and electrode-pairs is provided via a real-time on-screen display of a geometrically reliable icon representing the distal part of the Lasso catheter along with the electrodes’ positions. Left atrial reconstruction was obtained using a fast anatomical map algorithm. This method takes a continuous (non-gated) record of the NaviStar catheter’s movements. Based on this volume sampling, a surface reconstruction was built in accordance with the set resolution level to prevent left atrial volume overestimation due to respiratory movements. Once the map was completed, a 3D computed tomography scan was performed to optimize the left atrial reconstruction ( Fig. 2 ).
Remote magnetic navigation system
The RMN system (Niobe II; Stereotaxis, Inc., St. Louis, MO, USA) is a technological platform that uses a steerable magnetic field to remotely guide a supple catheter inside the heart . The steerable magnetic field contains two giant computer-controlled 1.8-tonne magnets that are positioned on opposite sides of the fluoroscopy table ( Fig. 3 ). A magnetic field of 0.08–0.1 Tesla is generated (according to the initial choice), such that the three small magnets that are incorporated parallel to the tip of the RF catheter allow for 3D navigation ( Fig. 4 ). The magnetic field is applied to a theoretical cardiac volume of 20 cm × 20 cm. The catheter tip may be directed very precisely using a vector-based computer system (Navigant system; Stereotaxis Inc., St. Louis, MO, USA) ( Fig. 5 ). This system operates by aligning the catheter relative to the magnetic field generated so that the movement of the catheter depends on changes in the direction of the two magnets in relation to each other. A computerized motor drive system (Cardiodrive; Stereotaxis Inc., St. Louis, MO, USA) advances or retracts the catheters, while its orientation in space requires a computerized work station (Navigant 2.1; Stereotaxis Inc., St. Louis, MO, USA). Using a keypad (arrows) or joystick, the catheter can be continuously advanced, retracted or even adjusted (from 1 mm to 9 mm). The second Niobe II generation allows for the magnets to be tilted at angles ranging from 40° left anterior oblique to 30° right anterior oblique. The constant application of the magnetic field during the ablation procedure keeps the catheter tip in permanent contact with the endocardial tissue throughout the cardiac cycle, thus improving the delivery of the RF current. Because the magnetic field exerts a weak force (15–20 g) and the catheter is very flexible, navigation inside the heart is very reliable, with a near-zero risk of perforation . The system is able to memorize certain data, such as the position of veins, and reutilize these vectors during the examination to facilitate catheter navigation or improve procedure times. In addition, automatic navigation is possible using NaviLine (Stereotaxis Inc., St. Louis, MO, USA), which allows for automatic processing by producing a line or surrounding veins.
