Repeat Ablation of Ventricular Tachycardia Using Robotic Magnetic Navigation

In this article, we present a case of a 58-year-old male patient with a previous Tetralogy of Fallot repair who underwent unsuccessful radiofrequency ablation for ventricular tachycardia (VT) in May 2019. The inability to reach critical anatomy likely contributed to the procedural failure. He continued to have incessant slow VT in spite of escalating antiarrhythmic medications. With the installation of a new robotic magnetic navigation (RMN) system at our facility, we performed a repeat VT ablation with successful results.

About RMN

The Genesis Robotic Magnetic Navigation System (Stereotaxis) has 2 magnetic pods positioned on robotic arms that rotate along their center of mass and allow the patient bed to be maneuvered against the procedural table as needed to transfer the patient at the start and conclusion of the procedure. The magnetic pods on the Genesis system are significantly smaller, lighter, and respond faster than its predecessor, Niobe II (Stereotaxis).¹ Once the patient is prepped for the ablation, their arms are securely wrapped with a sheet and held closely against their torso. The physician then achieves vascular access and places catheters in the heart. Once all the catheters are in, the magnetic pods pivot 90 degrees, creating a magnetic field centered at the patient’s heart (Figure 1). The physician and scrub tech can then break scrub and move into the control room. From the control room, they can utilize the Odyssey Vision monitor to complete mapping and ablation.²

The 8 French (Fr) magnetic navigation mapping and ablation catheter (THERMOCOOL RMT, Biosense Webster, Inc., a Johnson & Johnson company) has a flexible tip portion containing a series of magnets that allow the catheter tip to be directed by the magnetic field.³ The catheter is advanced and retracted using a small drive unit (Cardiodrive, Stereotaxis) connected to the patient drape near the site of catheter insertion that allows for movement in as little as 1 mm increments. The catheter responds to changes in the direction of the magnetic field, being pulled through the chambers and into contact with the target cardiac tissue. This allows for continuous stable focal contact with moving, flexible cardiac structures. This is fundamentally different than the interface of traditional catheters, where contact can be limited due to their stiff nature. In addition, movement in flexible and non-linear directions, as opposed to the limited curvature of traditional catheters, can allow for improved access to anatomically challenging locations.^4,5

Case Presentation

The patient is a 58-year-old male with a history of Tetralogy of Fallot repair in the 1980s. He has a history of paroxysmal atrial fibrillation, VT, ICD, congestive heart failure, moderate RA and RV dilation, ejection fraction of 33%, type II diabetes, and a CHA₂DS₂-VASc score of 2 (on rivaroxaban). His first ablation was performed in May 2019. His ablation was difficult due to a large, dilated RV and a posterior outflow tract with an overriding aorta that was difficult to get to despite using long sheaths. After his ablation, his VT was noted to be slowed to 90 bpm on his ICD but was still present frequently. This persisted despite escalating doses of antiarrhythmic medications, including sotalol at up to 120 mg BID.

He presented to our lab for repeat ablation with incessant monomorphic VT of 95-100 bpm that appeared to be outflow tract in origin. A 10 Fr SOUNDSTAR ICE catheter (Biosense Webster) was advanced into the right atrium for ultrasound mapping of the RVOT, LVOT, and aortic cusps. The RMT catheter was positioned into the RVOT through an 8.5 Fr SRO sheath (Abbott). Mapping was performed, and the earliest activation area was 35 ms pre-QRS located along the septal side of the RVOT. This area was accessed easily using the Genesis RMN System, and corresponded with the area unable to be adequately mapped and ablated during the patient’s prior procedure with manual catheters and sheaths. Multiple lesions were made using 50 watts at the earliest area of activation and around the border zone of the RVOT patch, but they had no impact on the VT. The distal coronary sinus/anterior intraventricular vein was also mapped from our right-sided access, but showed less favorable findings.

Next, we changed the 4 Fr arterial sheath to an 8.5 Fr LAMP sheath (Abbott) placed over the aortic arch to facilitate easy placement of the RMN catheter into the aortic root. Heparinization was initiated and the ACT was kept at 250 to 300 seconds. The RMT catheter was removed from the RVOT and placed in the aortic root where both the right and left coronary cusps were carefully mapped, including the ostia of the right and left coronary arteries. The ablation catheter was then advanced through the aortic valve and mapping was continued underneath the valve leaflets. The earliest area of activation proved to be in the right coronary cusp at 39 ms pre-QRS. Ablation with up to 40 watts of power in this location was performed. This resulted in cessation of the VT within 10-15 seconds of ablation. VT and PVCs were no longer inducible. With the use of isoproterenol at 5 mcg/min and burst pacing, the VT returned. More lesions were applied to both the right coronary cusp and again from the RVOT at the site most anatomically adjacent on 3D mapping using between 40 and 50 watts (Figure 4). At 30 minutes post ablation, the VT was uninducible. ICE imaging showed no post-procedure pericardial effusion. All sheaths and catheters were removed, and hemostasis was achieved. The patient was admitted overnight for observation.

The patient was seen at 2 weeks post procedure, and his ICD showed no episodes of VT but several short episodes for paroxysmal AF. The patient reported feeling well and noted significant improvement compared with his months spent in incessant VT.

Discussion

This case report exemplifies several advantages of magnetic navigation for the mapping and ablation of complex arrhythmias. The key characteristic of the ablation catheter include that the distal end of the catheter is soft and flexible. This tip is directed by 4 magnets creating 3 hinge points, allowing for unlimited degrees of directionality. Even with cardiac and respiratory motion, the magnetic field created within the patient can hold the catheter’s magnetic tip in constant contact with the endocardium with little to no risk of perforation.⁶ It is also less stressful for the operator when ablating near critical structures since the system can make small and precise movements. In addition, we have demonstrated the safety and precision of the system in complex anatomy. We safely and effectively mapped the aortic root region, including the ostia of the coronary arteries, which we routinely do with RMN in nonischemic patients, as well as the distal coronary sinus, which was easily accessed by the flexible catheter. This approach allows clear understanding of important anatomical relationships and eliminates the need for angiography. We have found the precision and safety of the Genesis RMN System to be of significant advantage in many complex cases.

The Genesis System is able to operate at 2 different magnetic strengths based upon the distance between the magnetic pods. When the pods are positioned 23.5 inches apart, the magnetic field is optimal at 0.1 Telsa. In order to accommodate larger patients, the system can also function at 26 inches apart at .08 Telsa. Since the magnetic pods need to be so close together, traditional arm boards cannot be used. The patient’s arms need to be tucked against their torso and tightly wrapped with a sheet. Unfortunately, if a patient’s shoulder width is larger than 26 inches, they physically are not candidates for this RMN system. Another important limitation to this system is that all patients must be screened to ensure they meet the same magnetic safety criteria as any patient having an MRI. If a patient has any ferrous implants or foreign objects in the body, they are not eligible for this type of ablation.

Summary

Our early experience with the Genesis RMN System has been positive overall. We have already had a number of successful repeat ablations that we attribute to the magnetic catheters being able to maneuver safely through challenging anatomy. After several months of use, the lab staff and physicians have grown more confident and faster in using the technology. The feedback from physicians that have used older generations of Stereotaxis is that this system is much faster, more responsive, and very user friendly. In comparison to other types of robotic navigation systems, a magnetically driven system such as Genesis is much safer and carries significantly less risk of perforation. It has been incredibly exciting for our EP team (Figures 6 and 7) to be among the first in the world to have access to this exciting technology.

We would like to invite all interested to view a recent live case performed from our lab using this technology (https://www.roboticep.com/telerobotics/live). In addition, anyone interested in further information and involvement with robotics in electrophysiology is invited to join the Society for Cardiac Robotic Navigation (SCRN). The society sponsors regular academic meetings and web-based events where physicians, trainees, allied professionals, and industry personnel can interact with the goal of expanding knowledge, technological advancement, and adoption of robotics and automation in electrophysiology. 

1. Genesis. Stereotaxis. Accessed January 18, 2021. http://www.stereotaxis.com/products/
2. Stereotaxis RMN Catheter Reach. Stereotaxis. YouTube. Accessed January 18, 2021.  https://www.youtube.com/watch?v=4OfwshGjfbY
3. CARTO THERMOCOOL RMT Catheter. Biosense Webster. Accessed January 18, 2021.https://bit.ly/2Y5QH6l
4. Odyssey Vision System. Stereotaxis. Accessed January 18, 2021. http://www.stereotaxis.com/products/
5. Stereotaxis RMN Catheter Reach. YouTube. Published September 10, 2018. https://www.youtube.com/watch?v=4OfwshGjfbY
6. RMN Catheter Stability. YouTube. Published January 28, 2020. www.youtube.com/watch?v=0rbY3n70pjk