Learning Curve Affects Cryoballoon Ablation Success in Treatment of Paroxysmal Atrial Fibrillation
January 27, 2011 — At the recent Boston AF Symposium, conference organizer, Dr. Jeremy Ruskin, presented data from the STOP AF clinical trial showing that learning curve impacted cryoablation success in treating paroxysmal atrial fibrillation. Doctors who had more experience with the Arctic Front Cardiac Cryoablation Catheter system had better outcomes than those who had performed just a few cases.
Dr. Ruskin’s findings were based on the number of cryoablation procedures performed by each doctor in Arctic Front’s U.S. clinical trial, STOP AF. The FDA approved the Arctic Front in December based on results from STOP AF. In addition to controlling atrial fibrillation better than antiarrhythmic medication, the Arctic Front also led to a significant improvement in patients’ quality of life.
Arctic Front is the first balloon catheter, and the first catheter to use cryo energy, approved for atrial fibrillation ablation in the US. Cryo energy, which ablates tissue by freezing, may reduce certain complications, such as esophageal injury, that can be associated with the RF energy that is used in traditional ablation catheters. Since Arctic Front is a balloon catheter, it can ablate larger areas of tissue in a single application compared to traditional catheters, which require doctors to ablate tissue point by point, similar to creating a line by making one dot after another.
Using a balloon catheter to perform pulmonary vein isolation is new to most American doctors. European physicians who spoke at the Heart Rhythm Society meeting in May 2010 speculated that some complications seen in STOP AF were related to learning curve. They suggested there would be fewer complications when American doctors become more proficient with the device and new technique. For instance, in Europe, where Arctic Front has been used for several years, the incidence of phrenic nerve palsy following cryoablation is only 2% compared to 11.2% in STOP AF. Damage to the phrenic nerve can make it difficult to breathe, and the high complication rate in STOP AF surprised many doctors.
Dr. Ruskin’s presentation at Boston AF confirmed that learning curve did affect both success and safety. Specifically, doctors who had performed 12–23 cryoablation procedures had a success rate of 90% compared to 56% for those who had performed only one or two cases. Success was defined as freedom from atrial fibrillation with or without antiarrhythmic medication. Of note, some patients counted as “successes” had more than one cryoablation procedure.
Similarly, there were no major adverse events when ablation was performed by doctors experienced with the cryoballoon compared to a 7% serious adverse event rate for those using Arctic Front for the first time. Dr. Ruskin also indicated that having a cryoablation procedure was the only predictor of freedom from recurrence of atrial fibrillation. Separately, he reported that the incidence of phrenic nerve injury was halved in the 80 patients who received cryoablation after the official enrollment in the STOP AF clinical trial had been completed. (Patients sometimes can receive treatment by an investigational device after trial enrollment has finished through what’s called a Continued Access Protocol—these patients are not included in the clinical trial’s official results.)
Dr. Robert Kowal, of Baylor Heart and Vascular Hospital, who provided some of the results presented by Dr. Ruskin, presented a poster at Boston AF on the learning curve seen in STOP AF. The poster showed that the ability to stop atrial fibrillation with a single cryoablation procedure was more pronounced with doctors who had more experience with Arctic Front. For instance, the single-procedure success rate was 70% for doctors who had performed 12–23 cryoablation cases compared to just 33% for doctors who had performed only one to two of them. Success was defined as freedom from atrial fibrillation without antiarrhythmic medication. In addition, experience with the new device allowed doctors to reduce the total procedure time by 15%, to 338 minutes, and reduce the fluoroscopy (x-ray) time by 24%, to 56 minutes, compared to first-time users.
To improve results, Medtronic, which manufactures the Arctic Front cryoballoon system, has established a training center where doctors learn how to position and manipulate the Arctic Front on animals before using the cryoballoon to treat patients.
Comments: The information presented at Boston AF is important for several reasons:
- It demonstrates that both success and safety improve when a doctor becomes more experienced with Arctic Front
- Doctors only need 12–23 cases to achieve good success rates
- Repeat ablation rates are reduced with experience
Since it may take time for a large number of doctors to become proficient with Arctic Front, patients interested in having the procedure immediately may want to consider seeking out a STOP AF clinical trial site.
For more details about cryoablation, see:
- Cryo Catheter Ablation System Approved for Treatment of Paroxysmal Atrial Fibrillation in US
- Study Shows Cryoablation Beats Antiarrhythmic Drugs for Treating Paroxysmal Atrial Fibrillation
- STOP AF Cryoablation for Atrial Fibrillation — Quality of Life and Technical Considerations
- About Arctic Front Cardiac Cryoablation Catheter
Disclaimer: Patients come first at StopAfib.org, and we do not compromise on that. While Medtronic, the maker of the system used in the STOP AF trial, is a donor to StopAfib.org, we believe that research findings from significant clinical trials must be reported to give patients an all-encompassing view of current and future treatment options. Therefore, we feel that it is important to report on this study.