Remote Magnetic Navigation is a new tool for complex ablations that is rapidly gaining popularity. The system allows precise control over the ablation catheter from a remote location. The Stereotaxis Niobe system has been deployed at several top arrhythmia centers around the world with great success. Many new centers are coming on-line because of the promise of the unprecedented control over the ablation catheter, reproducibility and decrease in x-ray exposure. The primary target of the system is complex ablations. The following case demonstrates a situation of a previously failed difficult ablation that was successfully completed with a remote navigation system.

Figure 1.

Remote Magnetic Navigation System (Stereotaxis).

Case Report
       The patient is a 58-year-old woman who was plagued by severe palpitations for many years. She was initially diagnosed with supraventricular tachycardia related to a Mahaim fiber in 2000. An ablation was attempted in 2001, but was unsuccessful. At that time, the patient was started on Sotalol, which was ineffective for controlling the patient’s frequent symptomatic palpitations. Therapy was changed to Flecainide. This strategy was initially effective, but the patient continued to have palpitations and more recently developed several episodes of syncope and near-syncope. In light of the above, the patient was taken to the electrophysiologic lab after discontinuing Flecainide. The patient was sedated with Midazolam and Fentanyl, and an electrophysiologic study was performed. The study confirmed the presence of a right lateral decrementally conducting accessory pathway with no retrograde conduction. Antidromic atrioventricular reentrant tachycardia could be induced. At this point, remote magnetic navigation was activated. Further mapping was performed through a remotely controlled CARTO RMT catheter (Biosense Webster, Inc., a Johnson & Johnson company, Diamond Bar, California). An electroanatomic map of the right ventricle suggested early ventricular activation during sinus rhythm, as well as during atrial pacing in the area of the distal septum. A right atrial map was created mapping the shortest atrioventricular conduction during pacing from various locations along the tricuspid annulus. This indicated that the atrial insertion of the accessory pathway is in the region of the lateral right atrium, close to the eight o’clock position on the tricuspid valve. Further detailed mapping in this area revealed an “M” potential. Radiofrequency (RF) current application in this area eliminated pre-excitation as well as tachycardia inducibility. The patient tolerated the procedure well, was discharged from the hospital, and had an uneventful recovery with no recurrences of symptoms.

Figure 2.

Carto RMT ablation catheter.

System Description
       Remote navigation system consists of three parts:
1. Two large permanent magnets that are installed on both sides of the procedure table in the electrophysiology laboratory. These magnets are used to create an external magnetic field that will direct intracardiac devices such as ablation catheters or guidewires. When not in use, the magnets are retracted to allow for easier access to the patient.
2. A diagnostic mapping and ablation catheter that has a small magnet imbedded in its tip. This allows for the catheter to be controlled by an external magnetic field created by the magnets that can be manipulated outside the patient’s body. The catheter has an extremely flexible shaft that does not restrict the motion of the catheter and allows for extreme deviation of the catheter tip since the shaft of the catheter has no structural function and works only as an electrical conduit for mapping and RF delivery.
3. The third part of the system is a computer that allows for the user to control and direct magnetic fields. The system has a built-in interface with a fluoroscopy system that allows to mark targets directly on a frozen fluoro image. Integration with a three-dimensional mapping system (CARTO) is also provided. Furthermore, the system can memorize multiple magnetic vectors and return the catheter to those positions at a later stage in the procedure. Finally, there is capability to create groups of vectors that can be connected into a continuous line for a linear ablation.
       The catheter is introduced percutaneously, just like any other electrophysiologic catheter, and is advanced into the heart. It can then be directed and manipulated via the computer system that is installed in the control room. Advancement and withdrawal of the catheter is performed using a sterile mechanical drive-train that is installed at the patient’s bedside, and is also controlled by the operator from the control room. The system is designed for conventional as well as three-dimensional electroanatomic mapping (using the CARTO system).
       An example of a live case of ablation using the Stereotaxis Remote Magnetic Catheter Navigation System can be viewed at the OR-Live website: www.or-live.com/motherfrances/1566.

Figure 3.

Electroanatomic map created via remote control.

Advantages of Remote Catheter Navigation System Over Conventional Ablation System
       This case highlights several advantages of the remote magnetic catheter navigation system. The foremost advantage of the system is catheter stability. There are certain arrhythmias that are considerably more difficult to ablate because of catheter stability. The Mahaim fiber is among them. Although it is not difficult to reach most locations on the lateral tricuspid annulus, it may be fairly difficult to keep catheters stable in this location. This is the reason why many electrophysiologists frequently employ the use of support sheaths for work in such locations.
       Another issue demonstrated by this case is the reproducibility of catheter navigation. It is not uncommon that one may uncover an interesting spot and face a dilemma of whether to apply radiofrequency energy immediately or do more mapping and subsequently attempt to return to the same spot. The advent of three-dimensional mapping has simplified this process greatly, by allowing us to tag points of interest and then return to those spots. However, depending on the location of the point of interest, returning the catheter to the exact same physical spot as has been marked on a three-dimensional map may on occasion be challenging. This problem is obviated by the remote magnetic navigation system. The system records all of the three-dimensional coordinates of the various catheter locations, and once a spot is tagged on the system, one can return to it essentially instantaneously by clicking on the saved tag.
       One of the limitations of ablation of Mahaim fibers is that these fibers typically are very sensitive to pressure. It is not uncommon to spend a significant amount of time mapping the pathway and then have a transient cessation of conduction because of catheter trauma. This may be extraordinarily disruptive to the ablation procedure, because sometimes Mahaim fibers do not recover conduction for hours after they have been traumatized by mechanical pressure. The amount of force that is exerted by the magnet in this system is sufficient to keep contact with the endocardium, but is not sufficient to traumatize the fibers. Over the last three years of using this system, I have never seen an accessory pathway “bumped” by a magnetic catheter.

Dr. Stanislav Weiner.

Dr. Peter Cheung.

       In this particular case, the accessory pathway was not difficult to navigate to; however, there are some locations that may be challenging as far as access. This certainly would be the case with some parts of the left atrium (for atrial fibrillation ablation procedures). In these situations, the remote magnetic navigation system may be quite helpful as well, because the shaft of the catheter is not involved with catheter manipulation and allows for a greater flexibility of the catheter. This facilitates access to certain areas that may be otherwise difficult to navigate to.
       Finally, the remote magnetic navigation system is quite instrumental at reducing operator x-ray exposure by allowing the conduct of most of the procedure from the control room. This may be less relevant to simple arrhythmias, but it becomes rather important in the mapping and ablation of more complex arrhythmias such as atypical flutter, atrial fibrillation or ventricular tachycardia. This is an important feature of the system given the fact that the incidence of simple arrhythmias has remained relatively stable over the last several decades, whereas the amount of time that is devoted to the more complex arrhythmias in the EP lab has grown exponentially.

Conclusion
       This case demonstrates some of the advantages of the new technique of remote magnetic catheter navigation, which allowed us to ablate an arrhythmia that was previously difficult to handle. It shows some of the strengths of the system that may be applicable for more complex procedures that are facing electrophysiologists today. While the true role of this system has not yet been defined, we are excited to be at the forefront of the research that will define the position of this new technology in our armamentarium. We are excited at the possibility of improving the efficiency and reproducibility of arrhythmia control procedures.