Drs Andrea Natale, Texas Cardiac Arrhythmia Institute, Austin, USA, and Carlo Pappone, San Raffaele University Hospital, Milan, Italy, debated at the Boston AF Symposium the merits of magnetic (Stereotaxis) or robotic (Hansen Medical) navigation for catheter ablation of atrial fibrillation. Cardiac Rhythm News asked the two doctors to write on why each of the systems is preferable for guiding AF ablation.
“Robotic navigation allows accuracy”
By Andrea Natale
In this debate, each speaker argues the “pro” and “contra” of each technology irrespective of their own personal opinion. Cather ablation although a well established curative modality for the treatment of atrial fibrillation has also its drawbacks and weaknesses, such as operator dependency and consequently reproducibility, inadequacy of mapping, inadequacy of lesion size, inability to reach the target sites, catheter stability and catheter contact pressure. New technologies such as robotic catheter navigation and ablation either with magnetic steering or with electromechanical guidance have emerged in the recent years aiming at solving these issues. The scope of this commentary is to support the reasons why robotic navigation is preferable to magnetic navigation for guiding AF ablation.
Safety: Both systems have shown safety for the ablation of atrial fibrillation.
Magnetic navigation has minimal risk of perforation. Although the robotic system carries a risk of perforation, different studies have shown that after a short “learning curve” the complication rate overlaps that shown with manual ablations. The world wide robotic experience presented at the AHA 2008 reported an overall complication rate of 1.1% in more than 1,300 cases with a 1% risk of perforation. This rate equals or is lower than the rate reported with manual manipulation in the world wide survey. However, safety and efficacy go “hand in hand”. In fact, the 4mm and 8mm catheters used for AF ablation with the magnetic system, although safe, do not achieve electrical isolation, have a high recurrence rate and are prone to charring. Although no stroke has been reported, this finding exposes the system to a risk that reduces his potential utilisation for atrial fibrillation ablation. Indeed, even though more than 20,000 cases have been performed worldwide with magnetic navigation, only a minority is AF ablations.
Efficacy: Published data with robotic technology support the concept that such systems can achieve acute pulmonary veins isolation and long-term success which overlaps and sometimes is better than in manual cases. Magnetic navigation with the 4mm and 8mm catheters so far available for the ablation of AF has not shown favourable results due to several reasons. The advent of the magnetic irrigated catheter tip may solve this issue but needs to be proven. In our results with the 4mm catheter tip we concluded that: “Whether the lack of isolation depends exclusively on the type of ablation catheter used for the procedure requires further testing”. With this conclusion we wanted to highlight the importance of catheter contact and catheter pressure. Contact and pressure applied by the catheter to the target ablation site are key points in the success of an ablation procedure. Both systems achieve good contact, although with different mechanisms, but the pressure applied to the targeted tissue is not dependent on the contact. With the robotic system pressure may vary and sometimes may be excessive. With the magnetic system, although the contact may be maintained during the entire cardiac cycle, the lower contact pressure may represent a relevant weakness and it could affect the ability to achieve permanent lesions in certain locations.
Costs: Economic consideration needs to be taken into account. Both systems are expensive. However, the robotic system has several advantages when compared to the magnetic. It fits pre-existing EP laboratories, it can be installed to serve multiple EP rooms, it uses existing commercial catheters and can be used with different 3D mapping systems. The magnetic system, on the other hand, requires a higher initial investment and the room needs to be properly shielded. It is, however, possible that the cost per case could be slightly lower with the 4mm and 8mm tip. Whether this remains true with the newly released open irrigation magnetic catheter is not clear.
Workflow and clinical experience
We believe that the robotic system provides a workflow which more closely resembles the one we are used to with manual manipulation.
When using the robotic system there is a natural and linear correlation between the movement the operator would like to do and the actual movement performed by the system. In fact, the robotic allows accurate and direct placement of the catheter tip, regardless of image orientation, and is designed to replicate physician hand movements at the workstation.
On the contrary, the magnetic system requires a double manoeuvre. First the operator has to change the vector of the magnetic field and then, with an additional movement using the groin advancer, he can place the catheter at the intended location. This could result in a longer time to reach each targeted site. This could affect the total procedural time and the physician’s frustration. Interestingly, both systems resulted in lower fluoroscopy time for the physician and in some cases for the patients.
In summary, both systems try to answer the need for easier navigation during atrial fibrillation ablation. With the robotic system this can be achieved at a lower cost while preserving the workflow of standard manual procedures.
Luigi Di Biase1,2,3, Andrea Natale1,4,5
1 Texas Cardiac Arrhythmia Institute at St David’s Medical Center, Austin, Texas, USA;
2 University of Texas Medical Branch, Austin,
3 Department of Cardiology, University of Foggia, Foggia, Italy;
4 Consulting Professor, Division of Cardiology, Stanford University, Palo Alto, California ,USA;
5 Clinical Associate Professor of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
“Magnetic navigation enhances capability”
The recent development of curative catheter ablation techniques for AF has made this job, once more, operator-dependent, and more sensitive to technological improvements. An increasing amount of published information has provided the background for developing a standard ablation scheme capable of curing paroxysmal AF in approximately 90% of patients; furthermore, in high-volume EP labs, even chronic AF can be safely and effectively treated. Performing an AF ablation requires a solid theoretical background and a long learning curve because of the complexity inherent in navigation, recognition of targets, and ablation of pathological tissues.
Stereotaxis technology is a new concept to introduce robotic- and computer-control to all manoeuvres inside the left atrium, in order to allow the physician to focus on what to ablate, rather than how to ablate. This system consists of two permanent magnets which are installed in a special-designed EP lab; this can represent an issue in terms of initial costs.
The physician can, with a computer, easily control the direction of this magnetic field, thus controlling any magnetic material inside the field itself, such as a magnetic catheter inside the heart. This technology enables automation of all phases of catheter ablation, independently of manual skills.
What can this technology offer over other systems like Hansen?
Automatic mapping: The system gives the opportunity to acquire anatomical points in every cardiac region independently of complex anatomies: the operator can focus mainly on electrical signal analysis. Over-stretching of the cardiac wall – often seen during mapping with standard catheter (by hand or with the Hansen system) – is avoided, meaning the left atrium retains something closer to its real shape and volume.
Automatic navigation: It enables the physician to reach all anatomical points of the reconstructed anatomy, just by double-clicking on the shell. With the new version, we also have the option to design linear and circular paths on the cardiac shell (Naviline feature): after having chosen the step density (1 to 3mm), the physician can move along the line with high precision, just by clicking forward and backward buttons.
Automatic ablation: Ablation can be precisely directed against specific substrates automatically navigating on previously designed linear paths. In the future, the system will be able to implement RF parameter control and signal analysis.
Simplification: The recently-released Odyssey system enables visualisation of all the machines used during an AF ablation procedure on a single screen, including the 3D system used to guide chamber reconstruction (CARTO or NavX), X-ray, polygraph and magnetic controls.
Integration: Stereotaxis is integrated with CARTO to enable easy control of both technologies with a single mouse. Future development will also allow control of polygraphs, RF generators, X-ray machines, and other 3D systems like NavX. Recently, the dyna CT software has been developed to acquire fast CT-like images of the left atrium directly in the EP lab; the true anatomy can be easily and quickly imported into the CARTO/NavX system. Naviline can be used directly in the registered CT anatomy.
Communication: Odyssey opens the way for single-beam transmission. It is possible not only to perform true “remote” procedures, but also to permit cooperation between centres in difficult procedures.
Dedicated catheters: What formerly represented a limitation – the lack of irrigated catheters – has been overcome. Magnetic catheters, irrigated and with flexible tips, could further enhance the advantages offered by magnetic navigation.
Multitasking: It can be used to manoeuvre a magnetic guide wire in the coronary venous and arterial systems to assist LV lead placement for cardiac resynchronisation therapy and guide wire navigation across complex coronary lesions and bifurcations for PTCA with or without stenting.
Not only the LA: Careful mapping with relatively low force contact permits mapping of tachycardia circuits and foci within the ventricular chambers, without introducing ventricular ectopic beats.
Feasibility: The use of a mouse to guide the ablation makes it feasible from the beginning. Unlike Hansen, no complex manoeuvres are necessary.
Learning curve: Our experience – published in the Journal of American College of Cardiology in 2006 – demonstrated that after 12 procedures a physician is able to use the system to successfully complete an AF procedure. The prerequisite for replicating this experience is represented by a solid theoretical background (for example pulmonary vein potential analysis).
Safety: It is impossible to perforate the heart due to lower-than-perforation-threshold maximum contact force and catheter fluidity. In our experience in more than 600 patients, we did not observe any left-based cardiac tamponade.
Efficacy: Our most recent data, which will be published soon, indicates that efficacy is similar to that reported in high volume centres for both paroxysmal and persistent AF. The experience is limited in patients with permanent AF due to longer follow-up necessary to judge success.
What about Hansen? This is a machine able to guide conventional catheters inside the heart, but…
Does not offer the automation previously described;
Perforation is worryingly frequent;
Systo-diastolic contact is not ensured;
The system is not integrated with other EP technologies;
It requires a longer learning curve, being less intuitive for the physician.
Of course it costs less, simply because it offers less.