Remote magnetic navigation

Remote Magnetic Navigation is an emerging technology in interventional cardiology. In this technique catheters with magnetic tips are steered within the patient, without the need for an electrophysiologist to maneuver the catheter or guidewire placement manually.

Remote Magnetic Navigation

This technique employed by companies such as Stereotaxis is unlike other robotic navigation techniques. The catheter is controlled by steering the distal tip with a magnetic field, making perforations virtually impossible.^[1] The engineering was developed at the University of Virginia, and the patent rights were later acquired by Stereotaxis, Inc. to market and develop a magnetic navigation system, according to its 2005 10-K filing with the SEC.^[2] The technology has been proven to reduce physician and patient exposure to radiation and procedure times, as well as enable more precise navigation of the vasculature with increased safety and efficacy.^[3] Additionally, remote magnetic navigation increases catheter stability while reducing the temperature required to successfully perform an ablation.^[4][5]

Traditional catheter labs in hospitals rely on the manual placement and steering of catheters by a physician. In interventional cardiology, catheters are used to map the cardiovascular system and to correct arrhythmias and atrial fibrillation, among other heart related problems, through a variety of methods including ablation. The patient is placed under a fluoroscopic system, such as a C-arm, to give the EP real-time feedback on the positioning of the catheter. In manual procedures, the physician must wear a lead apron due to radiation exposure, whereas with RMN, the doctor can conduct the procedure in a shielded room or at another location via a network connection. Then ablation catheters are used to burn scars in heart tissue to correct irregular rhythms. Apart from ablation, cardiologists use guide wires and catheters to place stents and other devices in the anatomy.

Remote magnetic navigation operates by using two large magnets placed on either side of the patient, and alterations in the magnetic field produced by the magnets deflects the tips of catheters within the patient to the desired direction. The EP operates the catheter placement and direction in a shielded room with screens and a joystick. The catheter itself is advanced by the joystick, instead of the physician's hands. Stereotaxis offers software which enables automated mapping and other advantages through its Navigant suite. Due to the lack of irrigated catheters, completing ablation procedures with magnetic navigation has been difficult, especially in the left atrium. Magnetic irrigated catheters for Stereotaxis's Niobe MNS have been recently approved by the FDA on February 26, 2009, and the catheters have been commercially available in Europe since November, 2008. Dr. Andrea Natale remarked that the new magnetic irrigated catheters are "revolutionary" for the treatment of arrhythmias.^[6] It is unclear what kind of procedure Dr. Natale performed and if it was included within the FDA approved procedures. As of January 2009, 18,000 total clinical cases were performed by magnetic navigation according to Stereotaxis's website, with a complication rate of less than 0.1%, representing a minute fraction of complications occurring with manual and other robotic navigation systems. The Niobe has yet to report an instance of perforation during a procedure. The long-term success, 6 months to 1 year after ablation, and cost effectiveness, has yet to have been approved by multicenter trials; however, single center studies have proven the Niobe superior in both categories when compared to manual techniques.

Installing an MNS may require that the catheter lab be equipped with steel plates and specialized equipment to prevent the magnetic fields from interfering with other equipment. Such installations can be costly and time consuming. According to the company, over 130 units have been installed worldwide, including the Cleveland Clinic, UCSF, the University of Michigan, Beth Israel, Kansas University Medical, Swedish Heart Hospital, Columbia Presbyterian, NYU and several hospitals in Europe, with close to 60 systems in the company's backlog.

Clinical Data & Efficacy in Cardiac Arrhythmia and Interventional Cardiology

The increased safety, reduced radiation exposure and shortened procedure times are well-documented in the literature; the efficacy of the system with non-irrigated ablation catheters remains contested against results from manual ablation procedures due to charring on catheter tips.^[7] Procedures with the newly launched, second-generation irrigated catheters currently demonstrate superior safety, efficacy and procedure time metrics compared to manual and other robotic techniques (publications listed below). Additionally, magnetic navigation has been found to reduce procedure times and costs for hospitals in AVNRT cases.^[8]

Currently, there are three main ablation catheters available with the Stereotaxis system, all created with Biosense Webster. They include 4 millimeter and 8 millimeter diameter non-irrigated catheters, both of which have received FDA and CE mark approval; Biosense Webster has also recently launched in the EU and the United States a Niobe-compatible magnetic irrigated catheter, the ThermoCool RMT.^[9] The ThermoCool RMT catheter is a member of Biosense's ThermoCool line of catheters, which have been recommended for approval in the treatment of Atrial Fibrillation by an FDA advisory panel.^[10] The ThermoCool catheters are the only ones recommended for approval by an FDA panel for the treatment of atrial fibrillation. The ThermoCool RMT catheter was not included in the recommendation since it has not been in use for enough time. Additionally, Biotronik has launched a gold-tipped magnetic irrigated catheter in Europe.

There has been some clinical debate surrounding the superior efficacy of magnetic navigation relative to manual procedures for ablation with non-irrigated ablation catheters. In a paper published from the Cleveland Clinic, Di Biase et al. failed to reach 40% of the target sites for ablation in a set of patients, n=45.^[11] The investigators cite charring on the catheter tip as a main issue preventing effective lesions using the Stereotaxis 4 mm ablation catheter. According to Dr. Bruce Lindsay, Di Biase et al. used this catheter for pulmonary vein antrum isolation (PVAI) when the catheter was designed specifically for supraventricular tachycardia (SVT).^[12] Further, Dr. Carlo Pappone raises questions of the validity of Di Biase's study, citing that it included 20 investigators for only 45 procedures and that despite the charring concerns, they still continued to conduct the study. Pappone also stated that the investigators of the study likely used faulty techniques by applying RF too long and not aligning the catheter to the heart wall correctly.^[13] Two principals of the Di Biase study have since left the Cleveland Clinic, Dr. Andrea Natale and Dr. J. David Burkhardt, who now practice at the Texas Cardiac Arrhythmia Institute. Dr. Burkhardt is now a proponent of the Stereotaxis system as the company's chief medical officer, and TCAI has a Niobe installed. A study led by Katsiyiannis et al. from the Minneapolis Heart Institute involved performing ablation on 40 patients, 20 with a manual non-irrigated catheter and 20 with the Stereotaxis 4 mm catheter. The mean procedure time for the manual procedures was 279 minutes versus 209 minutes with the magnetic catheters (p<.001). After one year 15 patients from the manual group and 16 from the magnetic group were free from atrial fibrillation. The procedures performed on the Niobe had on average 19.5 minutes of fluoroscopy time, compared with 58.6 for the manual procedures.^[14]

Initial Experiences with the First Generation Magnetic Irrigated Catheter

During HRS 2008, European physicians presented abstracts about their initial experiences with the magnetic irrigated catheter, which was recalled in January and then relaunched in Europe in November, 2008. The studies cited below are from experience with the irrigated catheter that was pulled by Biosense Webster due to manufacturer specification issues and catheter-tip charring. Despite these issues, clinicians were able to achieve acute and long-term results and safety better than manual ablations.

• Koektuerk et al. (2008) from the Hanseatic Heart Center in Hamburg, Germany, were able to successfully block RAI in all patients with the irrigated catheter, compared to 89% of patients with the 8 mm non-irrigated catheter with "favourable procedural parameters."^[15]
• Reddy et al. (2008) investigated the use of the irrigated catheter in left-side ablation in 11 patients, eight of which were classified as atrial fibrillation, one as macroreentrant AT, and two as scar-related VT. All PVs were remotely isolated in the AF group, and the only unsuccessful ablation occurred with a deep-septal VT circuit.^[16]
• Dr. Carlo Pappone was able to successfully disconnect PVs in all 33 patients in his study without any major complications. In one case, he did find charring on the catheter. He stated, "Navigation and mapping was more challenging with irrigated-tip than with solid magnetic catheters probably due to their different architecture. Being hollow inside, the magnets used at the tip are smaller potentially reducing their responsiveness to the magnetic field. No major complications occurred during and after the procedure." ^[17]
• Koektuerk et al. (2009) find that 64.3% of patients were free of AF after 334 days since treatment in a sample of 28 patients using the first magnetic irrigated catheter without any procedural complications. Catheter tip charring was found in 57% of the cases in the study. They conclude, "Single procedure success rates of magnetic PVI are in line with manual AF ablation data."^[18]
• Chen et al. (2009) investigated two groups of patients, 37 and 44 cases respectively. For the first group, they find that 73% of patients undergoing treatment with the magnetic irrigated catheter were free of AF after a mean of 10 months after procedure. Stable sinus rhythm was obtained in all patients immediately after the procedure without complications. The investigators conclude, "RMN for ablation of AF using magnetic irrigated catheter is safe, with a short procedure and fluoroscopic time and a promising long-term efficacy."^[19]
• Santinelli et al. (2009) achieve an 82% long-term success rate in treating AF patients after 14 months. Acute success was 93% without any procedural complications and an average total procedure time of 80.5 minutes.^[20]

The Relaunched Second Generation Irrigated Catheter

• According to presentations at the Boston Atrial Fibrillation Symposium 2009, the magnetic irrigated catheter achieved a 95% acute success rate, with the procedures distributed as the following: CLAA (72%), VT (7%), SVT (9%), and AF (12%). Of the 127 complex left atrial fibrillation procedures, 97% (123) achieved acute success, with zero complications. The mean procedure time was 91 minutes, with an average fluoroscopy time of 16 minutes. Of the entire sample of 170, one patient observed a late pericardial tamponade (0.3%).
• Wissner et al. (2009) successfully achieved magnetic lateral PVI in 12/12 patients and Septal PVI in 11/12 patients without complications or catheter tip charring. They state, "Magnetically navigated remote controlled AF ablation using the second generation 3.5-mm MIT catheter is feasible and associated with a high procedural success rate without evidence of tip charring."^[21]

Despite his early criticism of the first version of the irrigated catheter, Dr. Pappone was more impressed with the relaunched version: "I am delighted with the results of my first procedures performed successfully with the newly available Biosense magnetic irrigated catheter. I am extremely happy with its performance, and believe that Biosense did an excellent job. Contact stability, lesion quality and overall mechanical performance are excellent, and I believe safety is likely to be exemplary."^[22]

Interventional Cardiology

Apart from its use in cardiac arrhythmia, magnetic navigation has been used in percutaneous coronary interventions (PCI) to cross lesions with magnetically steered guidewires. Once the guidewire is inserted, a delivery catheter traces the guidewire to deliver the desired treatment. The magnetic navigation system has been shown to produce equivalent high rates of efficacy, while reducing time and also contrast use, which can lead to serious complications from contrast-induced nephropathy.^[23] Individual cases demonstrating the unique capabilities of the system succeeding after failed manual PCI have been documented.^[24][25][26]

• Atmakuri et al. found that RMN was successful in 85% of difficult anatomy PCI cases, and also successful in 63% of cases in which manual PCI failed.^[27]

Similar Devices

• Hansen Medical offers the Sensei robotic catheter system, a device utilizing a system of pulleys to steer sheaths which guide catheters.
• Corindus Vascular Robotics , Waltham MA, has developed a vascular robotic system (The CorPath System) initially targeted at PCI procedures in the cath lab. Remote navigation is attractive since it removes the physician from the radiation used to monitor the catheter's progress.

A different track in the development of medical devices for ablation is to make the procedure easier to perform by development of catheters that make the lesions around each pulmonary vein in one operation. Another benefit is that no expensive imaging system is needed. Examples are:

• Ablation Frontiers Pulmonary Vein Catheter
• Bard HD Mesh Ablator Catheter
• CryoCath Arctic Front

References