After training at a high-volume tertiary care center where the primary method of atrial fibrillation (AF) ablation was using the cryoballoon technique, I joined a very busy practice in Ventura County, California. This cardiology group, consisting of eight invasive and/or interventional cardiologists, had never before had an electrophysiologist on staff. In contrast to the five other electrophysiologists who cover multiple other hospitals in addition to SJRMC, my practice is primarily at St. John’s Regional Medical Center (SJRMC). Together with St. John’s Pleasant Valley Hospital, these two hospitals have 411 beds, one dedicated EP lab (at SJRMC), one dedicated catheterization lab, and one dual-purpose lab shared with cardiology and interventional radiology services.1-2
AF ablation is perhaps one of the most important aspects of any clinical EP practice. Due to my experience performing approximately 200 cryoballoon ablations during fellowship and because of the published results of the FIRE AND ICE clinical trial,3 I believe cryoballoon ablation is faster, safer, and more effective than traditional radiofrequency ablation. Soon after starting my practice at SJRMC, I approached hospital administration about acquiring cryoballoon technology. Since the hospital has a limited number of labs, the hospital administration was very supportive of the idea because the cryoballoon technique is faster and takes less lab time. They acquired the Arctic Front Advance System (Medtronic), and I performed the first cryoballoon ablation in Ventura County on November 3rd, 2016 at SJRMC. Since then, I have performed 23 cryoablation cases (as of February 1st, 2017); five other cases have also been performed by another electrophysiologist at SJRMC. The majority of procedures have been performed for symptomatic paroxysmal AF. Below is a summary of protocols and our initial experience with the cryoballoon technique at SJRMC.
During their first visit, the benefits and risks of the ablation procedure are discussed in detail with patients; I often give patients the option to schedule a second brief visit to give them some time before making their decision. I obtain routine preoperative labs including a chemistry panel and blood cell count. In addition, I include a sedimentation rate test, which has helped me to uncover infection (i.e., cellulitis, urinary tract infection) in two patients before the procedure. I often obtain a CT scan of the chest with contrast (unless the patient has renal insufficiency), with focus on the left atrium and pulmonary veins (PVs). This test provides excellent information about the anatomy and size of the left atrium and PVs, as well as the absence or presence of intracardiac thrombus in the left atrial appendage. If the CT scan shows no intracardiac thrombus, I proceed with the ablation procedure; however, if it is not done or if it cannot rule out intracardiac thrombus, then I perform transesophageal echocardiography on the day of procedure and just prior to the procedure. I have had to abort two procedures because of possible thrombus or significant sludge in the left atrial appendage. Anticoagulation is held only the day before the procedure.
Medtronic’s Arctic Front Advance System is comprised of the CryoConsole, Freezor MAX Cardiac Cryoablation Catheter, Arctic Front Advance Cryoballoon, Achieve Mapping Catheter, and FlexCath Advance Steerable Sheath. Other equipment used during the cryoablation procedure includes intracardiac echocardiography or transesophageal echocardiography, tools and equipment for transseptal puncture, and diagnostic EP catheters.
Two sizes of the cryoballoon are available: 23 and 28 mm diameter. For practical purposes, the 28 mm is more commonly used. The catheter diameter is 10.5 French.
The mapping catheter, with loop size of 15 mm or 20 mm, has 8 electrodes at its tip for mapping the PVs. The 15 mm catheter provides the advantage of being able to further advance inside the PVs and its branches, while the 20 mm catheter provides better contact with the vein. If a CT scan is done, the size of the PVs can guide the choice of the catheter size.
The cryoballoon catheter is inserted via a steerable sheath. FlexCath (Medtronic) is the standard sheath for cryoballoon ablation. The inner and outer diameter of the sheath is 12 and 15 Fr, respectively. It is better to insert it via the right femoral vein, which provides straighter access to the heart. It may require using a 10 or 12 Fr dilator after obtaining access with an 8 Fr sheath and before inserting the FlexCath. When the interatrial septum is thick or floppy, advancing the FlexCath into the left atrium needs careful attention. While gently applying forward pressure, rotate the FlexCath in a clockwise/counterclockwise motion to work the sheath across the septum. A secondary approach is to confirm that the dilator is across the septum, slightly draw back the FlexCath, begin to rotate the sheath in a clockwise motion to direct it toward the RSPV, and then advance the guidewire to access the RSPV. Once the wire is positioned in the RSPV, gently apply forward pressure while rotating the sheath in a clockwise /counterclockwise motion to work the sheath across the septum. The DIREX Steerable Sheath (Boston Scientific) is an alternative sheath for this procedure; it has a larger (0.5 Fr) inner diameter compared to the FlexCath, and has a smoother tip to dilator transition.
The interatrial septum is visualized for transseptal puncture using intracardiac echocardiography (8 or 10 Fr AcuNav catheter, Siemens) or transesophageal echocardiography.
A number of diagnostic catheters can be used during the procedure. Unless a full electrophysiology study is required, I use a decapolar catheter to cannulate the coronary sinus and record the coronary sinus electrograms during the procedure. I use the same catheter for pacing and capturing the phrenic nerve when right PVs are ablated.
Using a three-dimensional mapping system is not necessary for cryoballoon ablation. Nevertheless, we routinely use EnSite NavX (Abbott), which helps to identify PV anatomy and electrograms, and reduce fluoroscopy time. We often obtain a voltage map of the left atrium, which provides some prognostic information about the degree of substrate for AF in that particular patient.
All cases at SJRMC are done under general anesthesia. There have not been any complications thus far with cryoballoon ablation.
Ultrasound is not routinely used for vascular access; however, with any difficulty after one or two attempts, access is then obtained by guidance of ultrasound. After sheath removal, hemostasis is often achieved by manual pressure. Purse-string suture was used in certain cases for large venous access closure, and the suture was removed the next day.
Transseptal puncture is done under both fluoroscopy and ICE guidance, and heparin is given immediately after the puncture is performed.
An intravenous proton pump inhibitor is usually given during the procedure to suppress the acidity of the stomach and for esophageal protection. The oral form of the drug then continues for one month after the procedure. There is no evidence that this practice prevents esophageal injury; however, it is a common practice among electrophysiologists.
Cryoablation is done following standard protocol, with a minimal cryoballoon temperature no colder than -55ºC and an ablation duration of 120-180 seconds. Often a second ablation is performed for each vein, even if the vein is isolated in the first ablation or has not shown electrograms. The exception to that is when the veins are close to the esophagus and the risk of esophageal injury is high.
Esophageal temperature is monitored using a one-sensor probe. The location of the esophageal temperature probe is adjusted for each vein, and the temperature is closely monitored by both the operator and the anesthesiologist. The ablation is stopped if esophageal temperature drops more than 4 degrees or to less than 30ºC, or if it drops rapidly. This is perhaps the most conservative approach among all recommendations. Among the first 23 patients in which cryoablation was performed, a lower esophageal temperature (28ºC) was accepted in one patient because of very close proximity of the esophagus and PV. In another case, the esophageal probe malfunctioned and was not showing any drop in esophageal temperature when a decrease was expected based on its proximity to the catheter; that ablation was immediately stopped, and the probe was changed before proceeding with any further ablation. With an adjustment of the cryoballoon position, an effective ablation can be performed that is safe for the esophagus. One useful maneuver is a slight counterclockwise rotation of the FlexCath after sealing the PV with the cryoballoon. That slight movement can often adequately separate the PV from the esophagus in anterior-posterior plane. Among the first 23 patients, there were only two cases (two veins) in which the PV could not be isolated using the cryoballoon technique; this was due to the difficult anatomy of the veins.
Another important safety issue is monitoring the phrenic nerve when right-sided PVs are ablated. In our lab, this is done by pacing and capturing the phrenic nerve at above the level of the cryoballoon throughout the ablation time. The diaphragmatic capture is monitored constantly by palpation of the abdomen by the operator. With any decrease in intensity of the diaphragmatic capture, the ablation is stopped. One confounding factor is the pacing catheter stability; with catheter movement, the diaphragmatic capture might be lost. There has not been any effect on phrenic nerve in any of our patients.
The total procedure time for the first few cases was between 120-150 minutes, and has decreased to 90-120 minutes in the last few cases. This is a shorter procedure time than the mean total procedure time (124 minutes) reported in the FIRE AND ICE trial, which was performed in experienced centers.3 The total fluoroscopy time for our first few cases was between 20-30 minutes, and has decreased to 15-20 minutes in the last few cases. The amount of contrast used to confirm the appropriate position and contact of the balloon and PVs has been between 10-30 cc, and is mainly dependent on the venous anatomy. A few of the EP lab staff were specifically trained by Medtronic for this procedure and scrubbed for the cases. Training included one in-person session with the electrophysiologist reviewing all the steps of the procedure and required equipment. After the first 20 cases, other EP lab staff have started to learn and scrub in for the cryoablation procedures.
Patients are monitored overnight at the hospital and discharged home the next day. Follow-up visits take place at one week (in-office EKG) and at two months (ambulatory EKG). Ambulatory EKG monitoring time is between 3 to 14 days.
Our cryoballoon ablation program, the first in Ventura County, involved a close collaboration between the hospital administration, cardiology group, and Medtronic. Within the first three months of initiating the program, a total of 28 procedures were successfully performed. No complications were observed. In the second month after initiating the program, the total procedure time was less than the average reported at the FIRE AND ICE trial, in which the procedure was performed in experienced centers.
Cryoballoon ablation can be safely and successfully performed at community hospitals where AF ablation is already being performed using a radiofrequency technique.
Disclosure: The author has no conflicts of interest to report regarding the content herein.
- St. John’s Regional Medical Center. Wikipedia. Published October 18, 2015. Available online at https://en.wikipedia.org/wiki/St._John’s_Regional_Medical_Center_(California). Accessed February 15, 2017.
- St. John’s Pleasant Valley Hospital. Wikipedia. Published October 18, 2015. Available online at https://en.wikipedia.org/wiki/St._John%27s_Pleasant_Valley_Hospital. Accessed on February 15, 2017.
- Kuck KH, Brugada J, Fürnkranz A, et al. Cryoballoon or Radiofrequency Ablation for Paroxysmal Atrial Fibrillation. N Engl J Med. 2016;374:2235-2224.