John Day, MD, FHRS, FACC
The Journal of Innovations in Cardiac Rhythm Management
Director of Heart Rhythm Services
Intermountain Medical Center
Salt Lake City, UT
I can hardly believe that summer has come and gone, and the kids are now back to school. In this issue, our second anniversary of the Journal's launch, I would like to focus my thoughts around the concept of whether we can wean ourselves off of traditional fluoroscopy, in hopes of improving the efficacy and safety of electrophysiological procedures for both our patients and for ourselves. In particular, I would like to touch on the excellent article that you will find within this issue, submitted by the Leipzig group, which focuses on the new and innovative MediGuide technology.
As mentioned in my previous commentaries, I am particularly concerned about the occupational risks of electrophysiologists. It also concerns me that we rarely discuss these “occupational hazards” at our meetings or in our EP journals. I remember too well the “badge of honor” that we used to wear during our fellowship training with regards to the long EP cases and the accompanying excessive fluoroscopy exposure. Now, as I am in middle age, and suffer from a bad neck from years of wearing lead, I fear that I am at a higher risk of cancer, similar to many of my older EP colleagues. I long to be totally free from wearing lead and radiation exposure. I do not want to spend my “golden years” in chronic spinal pain, nor do I want to spend my retirement years undergoing chemotherapy for a cancer that could have been avoided.
It is within this context that I eagerly await the new imaging systems that can allow for safer procedures, not having to wear lead and without exposure to radiation. While we certainly are not there yet, the aforementioned manuscript within the Innovative Techniques section of this issue, titled Non-fluoroscopic Catheter Tracking for Interventional Electrophysiology Procedures: The MediGuide System, describes initial experiences with the MediGuide system and is an excellent first step in achieving this dream.
Just what exactly is MediGuide? MediGuide is a technology purchased by St. Jude Medical in 2008 for 300 million U.S. dollars. This technology allows for real time 3D visualization of catheters or wires (basically anything with a sensor at the tip) onto a previously acquired fluoroscopic image. Thus, at the beginning of the case, a short cine loop is obtained. Once the cine loop is acquired, catheters can be “seen” without further fluoroscopy as long as the procedure is within this field. From a hardware standpoint, MediGuide is basically an anatomical GPS transmitter that attaches to the fluoroscopy detector of a conventional flat panel x-ray imaging system.
With the use of MediGuide and sensors attached to the irrigated tip ablation catheters, the Liepzig team was able to perform atrial fibrillation ablation procedures with less than 2 minutes of total fluoroscopy time, and less than 6 minutes of fluoroscopy time for CRT implantations (there are no pacemaker leads yet with the MediGuide sensors attached).
This is a huge advancement in the field of catheter ablation, and to a lesser degree in CRT implantation because sensors are not yet attached to pacemaker leads. Worldwide, fluoroscopy varies widely depending on the procedure, with fluoroscopy times for AF ablations ranging from 5 to 90 minutes (an average AF ablation fluoroscopy time is likely 30 to 50 minutes). I don't even want to know how much radiation I am exposed to with CRT implantations, given how incredibly close you are to the fluoroscopy beam in the LAO position. Regardless, this is far too much radiation exposure for our patients and us.
The beauty of MediGuide technology is that it potentially allows for catheter ablation procedures without having to wear lead once the cine loop is obtained. Someday, when sensors are incorporated into pacemaker and ICD leads, we may be able to implant new devices without wearing lead. Moreover, the technology also compensates for patient movement caused by respiration and heart motion and potentially allows for more accurate imaging when image integration is performed with CT or MRI images with AF procedures.
While innovative new technologies like MediGuide are currently available in Liepzig, when will they be available in the U.S.? Currently, the MediGuide system in the U.S. is very limited. It is anticipated that by the end of the year, MediGuide will be compatible with the EnSite NavX 3D mapping system as well as one irrigated tip ablation catheter. In the CRT world, a cannulation catheter, subselection catheter and guidewires with Mediguide sensors for left ventricular lead are already FDA approved.
Certainly, one could ask what are the current limitations of this first generation MediGuide system. Probably, the biggest limitation is that we are still tied to fluoroscopy, and have to work within a “fluoroscopic environment”. Cine images have to be obtained at the beginning of the case and the operator has to use fluoroscopy to visualize catheters being advanced to the heart. In addition, there are not yet sensors incorporated into the tip of the transseptal needle, so the operator would need to use fluoroscopy or intracardiac echo to perform a transseptal puncture as part of an AF ablation procedure.
Also, the images obtained with MediGuide are rather limited in this first generation system. Catheters are not displayed linearly like you would see with “real fluoroscopy” but rather as color animated catheter tips as the sensors are only located at the tips of catheters. Thus, you can see these color animated catheter tips move in real time pasted on the background of a fluoroscopic image which can be displayed in two views (i.e. AP and LAO).
Another important limitation is that MediGuide is only compatible with the Seimen's Artis Zee fluoroscopy system. Thus, for many facilities, it would require a very costly new fluoroscopy system, which is beyond most EP lab capital budgets in these challenging economic times. Hopefully, there will not be too much of a price premium with these catheters once they are approved in the U.S.
Despite these limitations, MediGuide and other systems currently being developed by other companies will hopefully allow us to finally rid ourselves of lead and unnecessary radiation exposure. I am sure you will find this article from the Liepzig group most interesting and hope that, as always, you will send me your comments, thoughts, and suggestions regarding this Journal.
Editor's Note: The August issue of The Journal of Innovations in Cardiac Rhythm Management published an incorrect statement within “Cardiac Resynchronization Therapy: Improving Patient Selection and Outcomes” (pp. 899–904). This article states the PROSPECT trial included 4,000 patients, though the total was just over 400. The PROSPECT study did not disprove all previous center studies. We apologize for this error.