- Remote magnetic navigation
Remote Magnetic Navigation, or Stereotaxis, is an emerging technology in interventional
cardiology. Catheters with magnetic tips can be steered within the patient, without the need for an electrophysiologistto maneuver the catheter placement manually. Unlike other robotic navigation techniques, the catheter is controlled by steering the distal tip with a magnetic field, making perforations virtually impossible. 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. [http://library.corporate-ir.net/library/17/179/179896/items/206241/StereotaxisInc10K.pdf]
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 flouroscopic 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. [http://www.stereotaxis.com/files/videomodule/@random44e629cb10050/animated_mag_still.jpg] The EP operates the catheter placement from a side table with screens and a joyce stick. 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. Irrigated catheters for Stereotaxis's Niobe MNS have been approved and will likely be brought to market by the latter half of 2008 through its partner, Biosense Webster. Due to the increased precision of catheter placement, the Niobe system is used mainly for complex procedures. As of January 2008, 15,000 total clinical cases were performed by magnetic navigation, 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.
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 100 units have been installed worldwide, including the Cleveland Clinic, UCSF, the University of Michigan, Beth Israel, Kansas University Medical, OHSU and several hospitals in Europe, with close to 60 systems in the company's backlog. Due to the cost of the systems and the need to outfit catheter labs for magnetic fields, product adoption has been slow but accelerating.
Hansen Medical offers a robotic catheter placement device, the Sensei, which claims to have similar advantages as the Niobe without the higher initial capital cost and construction. As of June 31st, 2008 over 31 Sensei systems have been installed across the world, with over 600 procedures performed. The Sensei operates by guiding standard catheters through a manipulated sheath through the patient's anatomy. The doctor performs the procedure at a side cart with no tactile response for force, but rather uses technology called "IntelliSense" to deduce forces applied. IntelliSense mathematically estimates the pressure the catheter exerts on heart tissue to help the doctor avoid perforations. Because of the sheaths multiple degrees of freedom, force detection at the distal tip has remained a challenge for Hansen's engineers. The system uses a series of pulleys to manipulate a snake-like sheath carrying the catheter. The sheath is 14 French in size, allowing for standard size catheters to be used. Because of safety concerns, the number of EP procedures has decreased 30% from the first quarter of 2008 to the second quarter of 2008. The Sensei has FDA clearence for mapping procedures only, but doctors continue to expiriment with the system for ablations.
Despite hundreds of procedures at academic universities and FDA approval, clinical data and disclosures in the company's SEC filings indicate that perforations and safety concerns remain an issue. The system firmly places the catheter on the heart wall during ablation, which can lead to tenting of the heart muscle and ultimately perforation. At the ACC 2008 conference, Biosense Webster was forced to submit MAUDE filings to avoid confusion about perforation, thombrosis and tamponade complications from use with the Hansen system. [FDA Medical Device Adverse Event Filings, Biosense and the ACC: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1050182] [Biosense ACC Filing #2: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1050189] [Biosense ACC Filing #3: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1050184] [Reported May 8th: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1078312] In addition to the four complications reported through Biosense, Hansen has another ten officially reported complications since it's approval in late 2007. [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=926393 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=952110 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1008231 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1031116 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1034263 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1045536 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1045351 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1045350 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [ [http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1045349 Manufacturer and User Facility Device Experience (MAUDE) Database Search ] ] [June 25th: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1081315] A leading electrophysiologist, Andrea Natale, was one of the chief advocates of the Sensei system. However, at HRS 2008 he deemed the technology unsafe after achieving a 19% complication rate, much higher than the average 4-5% rate for manual ablations. [ [http://www.hrsonline.org/Sessions/HR2008/sci-prog/exp_webcasts.cfm Heart Rhythm 2008 Expedited Webcasts ] ] Reports from Dr. Natale and other doctors using the Sensei have raised concern that many more adverse events have occurred with the system than the documented 14 in the MAUDE database. This calls into question Dr. Fred Moll's claim that the Sensei system achieves a similar complication rate as manual procedures, as a substantial portion of Sensei procedures are performed in Europe. Doctors continue to use the system for ablation procedures despite the FDA's requirement that Hansen Medical place a sticker on the system and advertisements to warn doctors and patients that the safety of the system has not been established for ablation procedures.
Cornidus, an Israeli firm, is developing a remote catheter manipulator similar to the design of the Sensei. Remote navigation is attractive since it removes the physician from the radiation used to monitor the catheter's progress.
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