The cardiac program at Northeast Georgia Medical Center began in August 2002, with the opening of the Ronnie Green Heart Center and the start of Cardiovascular Surgery and Interventional Cardiology. The Cardiology Department began the program with a desire to achieve the highest level of clinical excellence in outcomes, quality, and technologically superior care. The goal has been to build a heart center that would perform at a national level. It was with this same focus on excellence that the Stereotaxis MNS was selected for the newest cardiac laboratory. In planning for the new labs, Interventional Cardiology and EP determined that the Stereotaxis system had great promise for improved outcomes and success with complex interventions and catheter ablations. Over the past year, the system s capabilities have exceeded our expectations, and the system is now utilized for almost all catheter ablations. A case study is presented to highlight our experience with the MNS.

Case Study
A 55-year-old man with coronary artery disease and normal left ventricular systolic function had a three-year history of symptomatic atrial fibrillation (AF) with early recurrence following sotalol therapy. Amiodarone had resulted in satisfactory suppression, but was not well tolerated. The patient elected to proceed with catheter ablation. This case was the first AF ablation performed with Stereotaxis magnetic navigation at Northeast Georgia Medical Center. Our approach for AF ablation at NGMC is outlined as follows. Pre-procedural imaging of the left atrium (LA) and pulmonary veins (PV) is performed with CT or cardiac MRI, and a transesophageal echo is done prior to the ablation. The ablation lesion set includes encircling lesions around the left and right pulmonary veins in an antral location with additional left atrial ablation individualized for each patient. Three-dimensional electroanatomic mapping (CARTO ^® electroanatomical mapping system, Biosense Webster, Inc., Diamond Bar, California) is used with guidance from intracardiac echocardiography (ICE) to further visualize the pulmonary vein anatomy. In addition, a circumferential mapping catheter (LASSO circular mapping catheter, Biosense Webster, Inc.) is used with the goal of PV isolation.

Cardiac CT scanning in this patient revealed a common left PV ostium and two separate right PV ostia (Figure 1). After transseptal access into the LA, the PVs were visualized on ICE, and the location of the LASSO at the PV os is verified. Next, three-dimensional mapping of the LA and PVs is performed. The mapping and ablation catheter (NaviStar RMT, Biosense Webster, Inc.) is maneuvered entirely remotely from the control room via the Navigant software (Stereotaxis, Inc., St. Louis, Missouri), which provides the interface between the electrophysiologist and the MNS. Fluoroscopic images are captured and saved in the Navigant window, and the catheter is directed from this information. With the click of a mouse and use of a joystick, the catheter is maneuvered to locations in the heart selected from the Navigant screen. The MNS permanent magnets provide direction for the catheter, and the catheter advancement system (CAS) advances and retracts the catheter. A crucial feature of the system is the MNS integration with the CARTO system. Points of interest on the CARTO map can be transferred to the Navigant software, and the catheter may be remotely directed to these points at the operator s discretion.

Another very useful feature is that the catheter tip is also superimposed on the static fluoroscopy images (Figure 2). In ablation for AF, this feature is particularly useful to avoid ablation in proximity to the pulmonary vein ostia. Movement of the LASSO catheter (which invariably occurs during these cases) therefore becomes less of an issue: once we have identified the ideal LASSO catheter position with ICE, a fluoroscopic image is saved into Navigant and remains valid throughout the case, even if the LASSO is dislodged. The live catheter tip remains superimposed on the original image. The need for repeated x-ray imaging is obviated. Thus, the Stereotaxis system permits constant integration of fluoroscopic and electroanatomic anatomic information without having to repeatedly step on the fluoro pedal, significantly reducing radiation exposure for both the patient and the physician, who can remain in the shielded control room.

Left atrial anatomy was mapped entirely remotely using the MNS, and all pulmonary veins were identified with the RMT catheter. A detailed three-dimensional map was constructed (Figure 3). Note the close correlation of the real-time CARTO map with the pre-procedure CT scan image. During this particular case, a second map had to be constructed due to patient movement and displacement of the CARTO magnetic location pad. Map reconstruction was expected to be frustrating, as this was our first use of the system for an AF ablation, but we were pleasantly surprised. The second map was constructed in almost half the time and was even more detailed (Figure 4). Moreover, the map was identical to the original map. In effect, we demonstrated the short learning curve involved with the MNS while showing the accuracy and reproducibility of the mapping.
Radiofrequency (RF) application was delivered around the pulmonary vein antral regions. With manual catheter manipulation, the operator is limited by the curve of the catheter and tolerance of applied torque. With the MNS, however, these issues are eliminated, as the tip of the catheter is the only part of the catheter maneuvered. The flexibility of the magnetic catheters combined with very consistent contact provide for exceptional catheter stability. For example, the right PVs are usually more challenging to reach and maintain catheter contact during conventional manipulation, but with the MNS, we used approximately the same amount of time to encircle the right PVs as the left PVs (Figures 5-7). At three-month follow-up, the patient was in sinus rhythm, off antiarrhythmic treatment, and without palpitations.

Discussion
This case highlighted several advantages of the Stereotaxis magnetic navigation system. Indeed, much of the original enthusiasm for this advanced technology was for its potential to enhance capabilities for complex ablation. In the case of ablation for AF, a number of advantages are apparent. Detailed and complete maps are generated, and as AF ablation has become more of an anatomically guided procedure, this enhanced capability may translate to improved results. We have also noted in cases of atypical macro-reentrant atrial flutter, the ability to fully define the entire circuit has led to successful ablation. In complex circuits, incomplete definition of the anatomy and failure to identify the critical portion of the reentrant circuit, as frequently occurs with conventional mapping, are contributors to ablation failure. Difficult to reach areas or regions where catheter stability and contact is poor often confounds accurate diagnosis and delivery of ablative therapy. Complex ablation is usually complex because of anatomic hindrances to a conventional catheter, thereby limiting diagnostic and therapeutic options and decision-making. Once the target is defined as in scar-related arrhythmias, ablation becomes straightforward.
Furthermore, inability to reach a target and achieve catheter stability to deliver ablative energy is another reason cases may be described as complex. With the Stereotaxis MNS, catheter navigation is superior to manual manipulation, and complex circuits are easier to define and ablate. In our opinion, magnetic navigation with the Stereotaxis system redefines the meaning of a complex case. AF ablation, macro-reentrant non-isthmus atrial flutter, and ischemic VT ablations all may be more easily performed in the future with widespread application of the technology.

Regarding standard mapping and ablation procedures such as for SVT, we have also concluded that magnetic navigation with Stereotaxis offers advantages to conventional manual catheter manipulation. For otherwise straightforward cases, we find that the primary advantage of the MNS is that it permits the electrophysiologist to remain in the control room to directly interpret and integrate all information: intracardiac electrograms, three-dimensional maps, catheter position, fluoroscopy, and entrainment data. EP study (EPS) and ablation for SVT provides a useful example of the workflow enhancements offered by digital technology. After vascular access and catheter positioning, the electrophysiologist moves to the control room for standard EPS and arrhythmia induction. Diagnostic maneuvers and analysis of electroanatomic mapping can all be performed from the control room without concern of catheter movement as the magnets maintain stable contact and catheter position. Importantly, during ablation, monitoring of AV conduction during RF delivery, operation of the RF generator, assessment of ablation data (impedance, temperature, power, etc.), observation for catheter movement on fluoroscopy and ablation effect are all easily monitored by a single individual from the control room (Figure 8). Finally, radiation exposure to the operators is eliminated during this phase. Implementation of the Stereotaxis MNS has permitted our EP lab staff to focus on the patient and the arrhythmia.

Limitations
At present, the predominant limitation to applying Stereotaxis magnetic navigation that we have found is the limited number of catheters available. Currently, only 4 mm tip ablation catheters are available. Thus, in situations where a large-tip electrode, irrigated tip electrode, or cryoablation is determined to be the best method of ablation delivery, a second catheter must be used if Stereotaxis mapping has been performed. We have found this aspect to be a limitation particularly for isthmus-dependent atrial flutter, left ventricular arrhythmias, ablation near the specialized conducting system, and other situations where RF delivered via a 4 mm electrode is sub-optimal. An 8 mm tip magnetically steerable catheter is being developed, and a full repertoire of magnetic catheters are planned for use with the MNS.

Conclusions
The Northeast Georgia Medical Center has developed the most technologically advanced EP lab in its region by implementation of the Stereotaxis MNS. Stereotaxis magnetic navigation has proven to be a superior method to conventional techniques for mapping in both complex and standard ablation.