This article appears in the following Europace issue: Spotlight Issue: Cardiac Imaging in EP and CRT [View the issue table of contents]
IMAGING IN CATHETER ABLATION FOR AF
Remote navigation systems in electrophysiology
Hanseatic Heart Center, Asklepios Klinik St Georg, Lohmühlenstr. 5, 20099 Hamburg, Germany
* Corresponding author. Tel: +49 40 181885 4487; fax: +49 40 181885 4435. E-mail address: bor.schmidt{at}asklepios.com
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Abstract |
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 Top Abstract IntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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Today, atrial fibrillation (AF) is the dominant indication for catheter ablation in big electrophysiologists (EP) centres. AF ablation strategies are complex and technically challenging. Therefore, it would be desirable that technical innovations pursue the goal to improve catheter stability to increase the procedural success and most importantly to increase safety by helping to avoid serious complications. The most promising technical innovation aiming at the aforementioned goals is remote catheter navigation and ablation. To date, two different systems, the NIOBETM magnetic navigation system (MNS, Stereotaxis, USA) and the SenseiTM robotic navigation system (RNS, Hansen Medical, USA), are commercially available. The following review will introduce the basic principles of the systems, will give an insight into the merits and demerits of remote navigation, and will further focus on the initial clinical experience at our centre with focus on pulmonary vein isolation (PVI) procedures.
Key Words: Robotic, Magnetic, Remote navigation, Atrial fibrillation, Ablation
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Introduction |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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In the past 10 years, interventional electrophysiologists (EPs) have extended the spectrum of arrhythmias that are amenable for catheter ablation. Today, atrial fibrillation (AF) is the dominant indication for catheter ablation in big EP centres (
65% in our hospital). The high prevalence of AF and the limited success of antiarrhythmic drug treatment fostered the absolute number of catheter ablation procedures. Additionally, the AF ablation strategies are more complex and technically challenging when compared with simple ablation targets such as accessory pathways. The complexity is expressed by relatively long procedure times (up to 4 h) and long exposure times to X-ray for both, the patient and the operator. While for the patient, a pulmonary vein isolation (PVI) procedure remains hopefully a single event, the operator faces the task to perform multiple physically strenuous procedures per day.
In order to achieve complete electrical PVI by circumferential ablation lines around the ipsilateral PVs, long contiguous linear lesions are mandatory and remain a challenge to the operator’s manual skills.1
Therefore, it would be desirable that technical innovations pursue the goal to minimize the physician’s exposure times to X-ray and the physical demands, to improve catheter stability in order to increase procedural success, and, most importantly, to increase safety by helping to avoid serious complications.
The most promising technical innovation aiming at the aforementioned goals is remote catheter navigation and ablation. To date, two different systems, the NIOBETM magnetic navigation system (MNS, Stereotaxis, USA) and the SenseiTM robotic navigation system (RNS, Hansen Medical, CA, USA), are commercially available. The following review will introduce the basic principles of the systems and will further focus on the initial clinical experience at our centre with focus on PVI procedures.
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The NIOBETM magnetic navigation system |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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The technology has been described in detail, previously.2
,3 In brief, a low-intensity magnetic field (0.08 Tesla) is applied to the patient by two permanent magnets positioned at either side of the patient. A special 8F mapping catheter containing three inner magnets must align parallel to the applied magnetic field. Precise catheter navigation is achieved by changing the orientation of the magnetic field. New catheters were designed to allow the combined use with an electroanatomical mapping system (CARTO-RMTTM, Biosense Webster, USA). Just recently, irrigated tip catheters had been in use during an evaluation phase at nine centres worldwide, but its application had to be stopped due to technical reasons in March 2008. |
The SenseiTM robotic navigation system |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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The function of the RNS has been described in detail.4
,5 In brief, it is an electromechanical system that realizes catheter navigation by two steerable sheathes (ArtisanTM, Hansen Medical, USA) incorporating an ablation catheter. The outer (14F) and the inner sheath (10.5F) are both manipulated via a pull-wire mechanism by a sheath carrying roboter arm that is fixed at the patient’s table. The robot arm obeys the commands of the central workstation positioned in the control room. Catheter navigation is realized using a three-dimensional joystick (Instinctive motion controlTM, Hansen Medical, USA) and allows a broad range of motion in virtually any direction. In general, all catheters <8.5F and all electroanatomical mapping systems may be used.
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Clinical experience using remote navigation |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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The initial reports describing the technology of MNS were published in 2002.2
Since then, it has been proven safe and effective in the treatment of all kinds of supraventricular and ventricular arrhythmias.3,6–13
The widespread application of the MNS for PVI was limited by the non-availability of an irrigated tip catheter. However, PVI using a solid 4 mm tip catheter was performed at different centres.14,15 Di Biase et al. reported satisfactory results with regard to navigation properties but failed to achieve complete PVI in >90% of the patients. As an adverse effect, extensive charring at the catheter tip was observed in one-third of the patients. Therefore, it was strongly discouraged to use a non-irrigated tip catheter for extensive ablations in the systemic circulation. However, no serious complications were observed in this series. Pappone et al. could confirm the data on manoeuvrability but did not assess PVI using a circular mapping catheter.
The issue of PVI was addressed in a stepwise approach at our centre. First, the system was used to map and to perform single radiofrequency applications at gaps in the circumferential ablation line during repeat double-lasso PVI procedures. Secondly, the feasibility, accuracy, and safety of electroanatomical left atrium (LA) mapping and tagging of the PV ostia were tested followed by a manual ablation. Thirdly, after the irrigated tip catheter had been launched, 28 patients underwent a completely remote magnetic PVI procedure.
During this initial evaluation, a ‘proof of concept’ could be obtained. Navigation to and stability at all relevant sites for a successful PVI was observed in the vast majority of the cases. However, major drawbacks of the remote magnetic navigation for PVI are still the prolonged procedure times and technical shortcomings regarding the irrigated tip catheter. Since, a learning process was observed and the number of patients treated is still small, a final conclusion cannot be drawn at the present time.
First reports on RNS stated the feasibility and safety to perform transseptal punctures and navigation in the LA.16 RNS has also been used for the ablation of supraventricular arrhythmias and AF.17 In a very systematic study, Reddy et al.5 reported on their initial experience using RNS in conjunction with image integration for PVI in animals and humans. In addition to excellent mapping properties, complete PVI was achieved in all nine patients without any serious complications. However, long procedure times (median 338 ± 89 min) were observed partially caused by a detailed evaluation of the navigation properties.
At our centre, the system was introduced into clinical practice in a stepwise fashion. Initially, cavo-tricuspid isthmus ablation was performed in patients with common-type atrial flutter. Secondly, after the completion of a manual LA electroanatomical reconstruction including the identification and tagging of the PV ostia using CARTO, a remote circumferential ablation was performed. Thirdly, the whole PVI procedure was performed remotely. The initial concern of an increased perforation risk due to the lack of tactile feedback could not be confirmed. No cardiac perforation occurred.
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Merits and demerits of remote navigation |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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The MNS appears to be a very safe technology (Table 1). The magnetic catheters are soft and render cardiac perforation virtually impossible. In addition, this allows gentle, non-traumatic mapping which may be advantageous in particular arrhythmias such as idiopathic ventricular tachycardia (VT).18
Clinical studies have demonstrated its application in supraventricular and ventricular arrhythmias. Moreover, all cardiac chambers including the coronary sinus and the epicardial space have been successfully accessed and mapped.12
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Software features including the storage of magnetic vectors and a design line concept facilitate mapping with the goal of future semi-automated procedures (Figure 1).
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Beyond catheter ablation, MNS has been used for the implantation of left ventricle (LV) leads in the coronary sinus and for wire navigation in phantom coronary vessels.19
,20 To date, the major drawback of MNS is the unavailability of an irrigated tip catheter, limiting its use for ablation in the systemic circulation and particularly for PVI. The initial experience with the catheter demonstrated feasibility and safety to perform circumferential PVI. The navigation to distinct sites (anterior inferior ostium of the septal PVs) was still difficult in some cases because of catheter design. Moreover, long procedure times mostly due to ineffective ablation lesions curtailed the initial enthusiasm.
If an electroanatomical mapping system is intended to be used, the operator is limited to CARTO. Regarding patient selection, it is still relatively contraindicated to expose carriers of implanted devices to the permanent magnetic field in order to avoid device malfunction or damage. Published data on device malfunction remain controversial.12,21
Regarding the installation of the magnets in an existing catheter-laboratory, special regulations have to be considered because of the permanent magnetic field.
The RNS seems to be a very safe technology, too. In the initial clinical studies, no major complications have been reported. Recent reports of RNS demonstrated the feasibility to perform remote PVI.5 Since virtually all mapping catheters can be used with RNS, the operator may choose his preferred electroanatomical system for complex procedures. The presence of implanted devices does not limit the use of RNS.
To date, no data on use of RNS for ventricular arrhythmias are available. Due to the large outer diameter of the outer sheath and the potential risk of perforation, the coronary sinus and/or epicardial space might not be entered which could limit the application of RNS in patients with long-standing persistent AF and/or epicardial VT. Two further arguments could limit the use of RNS for VT:1 a 14F vascular access is needed, which restricts the approach of the LV to a transseptal route.2 The reach of the inner sheath may be too short to map all parts of LV, unless the 14F outer sheath is inserted far into the left atrium. Another limitation of RNS could be the restriction to a distal bipolar recording because the map catheter has to be retracted to the inner sheath to achieve optimal stability. Finally, the operator is still navigating manually since RNS does not provide automatic features (Figure 2).
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Benefits and disadvantages in comparison to manual navigation |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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Any technical innovation has to prove superiority or at least non-inferiority to the gold standard. Both systems demonstrated excellent navigation and stability properties. No objective data exist since the stability is difficult to assess, but from the everyday clinical use, we can state that at the LA roof, both MNS and RNS provide good catheter stability.
Most published studies state a decreased exposure to scattered X-rays for the operator. However, till date, no randomized trial has evaluated this aspect. In our initial experience, the total fluoroscopy times in PVI are not shorter and most of the X-ray is used while standing next to the patient (transseptal puncture, PV angiography, Lasso manipulation, etc.).
Until today, both systems failed to shorten procedure times. Conversely, in a single comparative trial using MNS for ablation of atrio-ventricular-nodal re-entrant tachycardia, procedure times were even significantly longer for the MNS group.22 The preparation of the devices (registration and positioning of the magnets for MNS; flushing sheathes and gain transseptal access for RNS) is still time-consuming.
Working remotely does not only mean to be remote from the X-ray source but also being remote from the patient. This might bear the risk to oversee a potential deterioration in his clinical status or to overhear steam-pops. Careful nursing is therefore mandatory.
The experience with remote navigation is still preliminary and a conclusion with regard to long-term success cannot be drawn.
Nowadays, economic considerations are increasingly influence the physician’s decisions on the use of health care resources. Both systems add substantial cost to the total procedure. It remains to be evaluated, whether potential benefits will outweigh this investment.
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Future directions |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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The major drawback of MNS is the unavailability of an irrigated tip catheter. Since the initial catheter had to be recalled from the market, future improvements should focus on catheter technology. A fully automated PVI procedure that is initialized by a single mouse click would be the dream of most interventional EPs. However, the auto-map and design line features of the system still deserve further evaluation and development.
For the RNS, it will be mandatory to reduce the sheath size in order to extend the applicability to ventricular arrhythmias. In order to decrease cost, a cheap non-steerable irrigated tip catheter that can be used with RNS should be developed.
Further, it would be desirable that both systems could be used in conjunction with alternative technologies like the balloon catheters.
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Conclusion |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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Extending the spectrum of indications for catheter ablation has increased the complexity of the procedures. Two remote navigation systems were developed to facilitate mapping, increase catheter stability, and reduce the physician’s X-ray burden. Both systems could provide a proof of concept for various ablation procedures but still need further technological refinement to improve their applicability and demonstrate superiority to manual procedures.
Conflict of interest: K.-H.K. is consultant to StereotaxisTM.
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Funding |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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K.-H.K. received research grants from StereotaxisTM.
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References |
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TopAbstractIntroductionThe NIOBETM magnetic navigation...The SenseiTM robotic navigation...Clinical experience using remote...Merits and demerits of...Benefits and disadvantages in...Future directionsConclusionFundingReferences |
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