It is 6 am and my alarm clock is ringing. I am waking up to start another day as an EP fellow in a very busy ablation lab. I arrive at the hospital to see the EP lab schedule; I am assigned to “A Lab”, which means I will be in the ablation lab all day.
On this particular day, two atrial fibrillation (AF) ablations are scheduled, which was not atypical. This usually means a 10- to 12-hour day with about 8 hours of standing in 20–30 pounds of lead. By the end of the week, I would usually have a sore back. By the end of my fellowship, I would take “prophylactic” ibuprofen to curb the pain of a long week in the ablation lab. Not uncommonly, I would get a letter from the hospital radiation safety department notifying me that I was nearly exceeding my recommended dosage of radiation for the month. Some might say we had become the radiation shields for our attending physicians.
My guess is that my story is not uncommon. On the road to becoming a successful electrophysiologist are the necessary rites of passage that we all must experience. One of these rites that we have come to accept is standing through long, arduous cases in heavy lead and exposing ourselves to radiation on a daily basis. At the time, taking these risks seemed mandatory. The consequences of these risks, although understood, seemed to be remote and unlikely to affect me personally. It wasn’t until years later that I realized I had a choice to either continue to expose myself to these risks, or modify how I practice and perform my procedures to minimize future orthopedic injuries and risks related to excessive radiation exposure.
Recently I read an editorial by John Day, MD, from Intermountain Healthcare in Salt Lake City, Utah.1 In it, he describes a young woman who had two long ablations for a very difficult posteroseptal pathway. Years later she again presented to their center for cancer surgery, and he was asked to perform a cardiac clearance examination. Appropriately, he asks himself many self-analyzing questions on whether he is doing everything he can to reduce the unforeseen risks of radiation exposure for his patients, his staff, and himself. It is my opinion that we are obligated as physicians to reduce these hidden risks to all of those with whom we come into contact. This includes our patients, our staff, and ourselves.
Understanding the Principles of Radiation and Radiation Exposure
Effective radiation doses are calculated in milligray (mGy) and millisieverts (mSv), with milligray being the absorbed dose of radiation and millisieverts being the dose equivalent. Everybody in the EP lab should become familiar with these terms. Fluoroscopy times are an indicator of how much radiation was dosed, but the actual dose of radiation depends on the settings of the equipment (frame/second, pulse/second, collimation use, etc.). Although reducing your fluoroscopy time should be a goal, so should reducing your total delivered radiation dose by using methods to minimize the amount of radiation dosed by the equipment for each second of fluoroscopy.
Typical EP procedures can deliver between 15–30 mSv and can be as high as 50 mSv in a single setting. When you add to this a pre-procedure CT (which delivers approximately 15 mSv) and a repeat catheter ablation for another 50 mSv, you can see how radiation can quickly add up for the patient. In comparison, a typical chest X-ray delivers 0.1 mSv, and we are exposed to approximately 2.4 mSv per year from atmospheric radiation.
Risks of ionizing radiation include cataract formation, solid tissue cancer, and leukemia. There is less data to support a risk for increased prevalence of cardiovascular disease related to small doses of radiation. In the BEIR VII Report,2 it is estimated that with a single dose of 100 mSv, there is a 1% chance of developing a solid tumor or leukemia. With a dose as low as 10 mSv, there is a 0.1% chance of developing cancer. There are many anecdotal and case series of interventionalists with increased risk of neural tumors. Case-control studies have shown an increased risk of brain tumors with an odds ratio of 3.5–6.0. These risks are magnified in the pediatric population. Most theories support a linear dose-response relationship (with no lower threshold) between exposure to ionizing radiation and the development of solid cancers in humans. This implies that there is no “safe” dose of radiation. When we consider how many ablations and EP procedures are being performed in the US alone, the number of possible cancers being caused can be shocking.
ALARA (As Low As Reasonably Achievable)
These factors have contributed to the development of the acronym ALARA, which refers to attempting to achieve the lowest possible radiation dose while still making procedures efficient and successful. It is clear that in the EP lab, reducing radiation exposure is going to require a new set of skills, the adoption of new technologies, and an active effort from the whole EP team in order to achieve the goal of lowering radiation to the ALARA level. We also need support from our hospital administrators to invest in the proper technology to allow us to achieve these levels.
Reducing Radiation Exposure to the Patient
By reviewing some of the principles of physics and how radiation is dosed by our fluoroscopy equipment, we can further reduce the dose of radiation to try to achieve ALARA. Minimizing fluoroscopy time is clearly important but not always achievable. Older continuous fluoroscopy machines emit more radiation than newer pulsed fluoroscopy systems. If possible, upgrade equipment to the newer technology. Try to use and adjust the settings on your individual unit to minimize the dose delivered. Many contemporary systems have an “EP” mode that should be utilized, but we have found in our lab that we can further reduce the dose by decreasing the frame rate and still have acceptable imaging. Use the collimators to focus in on the area of interest. The image intensifier should be positioned as closely to the patient’s body as possible.
Reducing Radiation Exposure for the Operator and Staff
Clearly one of the best ways to reduce radiation exposure to ourselves and our staff will be to reduce the exposure to the patient. In turn, this will decrease the amount of scatter radiation emitted from the patient. Everyone involved in the case will benefit from this strategy. In addition, you should always wear personal protective equipment (PPE); this is usually in the form of lead apron glasses and a thyroid shield. I also include your radiation badge on the list of “must wear” PPE. Utilize fixed barriers whenever possible, such as the hanging lead shield when standing at the table and a fixed lead shield for staff who are required to be in the room for the entirety of the case. When not active in the case, stand away from the patient to maximize the inverse square law, which states that the further you are from the source, the weaker the intensity of the radiation.
Technologies to Reduce or Eliminate Radiation Exposure
Intracardiac Ultrasound. In our lab, the use of intracardiac ultrasound has become invaluable. It not only allows real-time three-dimensional mapping for complex atrial and ventricular procedures, but also allows us to reduce fluoroscopy by being able to visualize our catheters in the chamber of interest. We also utilize it to image the esophagus, assist with the transseptal puncture, and assess for complications during and after the procedure.
3D Mapping. The two systems commercially available are Carto (Biosense Webster, Inc., a Johnson & Johnson company, Diamond Bar, CA) and EnSite (St. Jude Medical, St. Paul, MN). Both systems allow one to recreate an electroanatomical map in three dimensions and to visualize catheters without the use of fluoroscopy. There have been many studies that have documented reduced fluoroscopy times by utilizing a 3D mapping system. Indeed, many centers are moving to completely eliminate radiation from the EP lab by using such systems. Inherent in the ability of the system to reduce fluoroscopy is that you must learn to create accurate maps and trust them. This is often easier said than done, and requires a commitment from the whole EP team to learn the system and its nuances. However, once this is done, we have found that we are able to routinely perform a complete pulmonary vein isolation with between 5–10 minutes of fluoroscopy (3–6 mSv).
Robotic Catheter Navigation. The two systems currently available are a robotic magnetic catheter navigation system (Stereotaxis, Inc., St. Louis, MO) and a remotely navigated steerable sheath (Hansen Medical, Mountain View, CA). The advantages of a robotic navigation system are numerous. They include decreasing radiation exposure to both the patient and the operator. The operator will usually sit in a separate location outside the main field of radiation. The burden of excessive weight from the lead apron is removed. Reproducible and precise catheter manipulation allows for less reliance on fluoroscopy. Mechanical trauma from magnetically controlled catheters is reduced due to the uniform force applied by the magnetic field. Complex procedures may benefit significantly from the use of robotics. Recently, many studies have been published supporting the fact that remote navigation not only reduces radiation exposure for the patient and operator, but can reduce procedure times overall.
In our center, we utilize a combination of the above technologies, including pulsed fluoroscopy (Siemens Healthcare, Erlangen, Germany), Intracardiac Ultrasound (Acuson, Siemens Healthcare, Erlangen, Germany), 3D mapping (Biosense Webster’s Carto 3 with CartoSound), and remote magnetic navigation (Stereotaxis). By combining the best of all technologies, we are able to achieve our endpoints successfully while minimizing long-term risks to patients from excessive radiation doses. We no longer routinely get pre-procedure CT scans to further reduce radiation doses. We are able to remove our lead after the venous access and transseptal is performed. It remains to be seen how newer cryo technologies (Arctic Front®, Medtronic, Inc., Minneapolis, MN) may begin to affect radiation doses delivered in the EP lab. There appears to be a learning curve with this new technology to reduce radiation exposure. This procedure may never become entirely “fluoroless”, but just as other technologies (intracardiac ultrasound and 3D mapping) have assisted us in reducing radiation, so might they assist the newer cryo technologies in eventually reducing their overall radiation exposure.
Therefore, it is imperative that we begin to recognize the “unseen risk” of excessive radiation in the EP lab, and take it upon ourselves to reduce or eliminate this risk as much as possible. This will require actively documenting and tracking fluoroscopy times and radiation doses on a routine basis. In our rapidly advancing field of electrophysiology, it is necessary for us to embrace new technology that will make our procedures safer, more efficient, and more efficacious. Recognizing the “inconvenient truth” regarding the risk of radiation will allow us to not only do what is best for our patients today, but decrease or eliminate their future risk for malignancy tomorrow.
- Day J. Letter from the Editor in Chief. Journal of Innovations in Cardiac Rhythm Management 2011;2:A8–A10.
- “Cancer Risks for Women and Children Due to Radiation Exposure Far Higher Than for Men.” Institute for Energy and Environmental Research Homepage. 7 July 2005. Accessed 15 Dec. 2011. http://www.ieer.org/comments/beir/beir7pressrel.html