NOVOSIBIRSK, RUSSIA. Most catheter ablation procedures use radiofrequency (RF) energy to create the lesions isolating the pulmonary veins (PVs) from the left atrium. However, it is also possible to create the lesions by freezing (Cryo) procedure. The Cryo procedure works by delivering liquid nitrous oxide under pressure through a catheter into a balloon (usually 23 or 28 mm in diameter) placed sequentially in each pulmonary vein. The liquid, when released, changes to gas resulting in cooling and subsequent cell death, thus creating an electrical barrier. Several clinical trials have shown that RF and Cryo procedures are about equally effective in attaining freedom from atrial fibrillation (AF) in patients with uncomplicated paroxysmal AF undergoing a first ablation. However, some patients require redo procedures and there is no data as to which procedure, RF or Cryo, is most effective in follow-up procedures.

A group of physicians from the State Research Institute of Circulation Pathology in Novosibirsk and Columbia University College of Physicians and Surgeons in New York now report their results of comparing the two procedures. The patient population involved in the trial consisted of 80 patients who had failed an initial RF pulmonary vein isolation (PVI) procedure for paroxysmal AF about 8 months prior. The average age of the patients was 56 years and 80% were male. They would appear to have no underlying heart disease (lone AF), but left atrial diameter was somewhat elevated at an average of 47 mm and a maximum of 55 mm.

The patients were randomly assigned to have a follow-up PVI using either RF energy (RF group) or Cryo (Cryo group). Prior to the procedure all participants had a cardiac monitor (Reveal XT, Medtronic) implanted so as to be able to determine the AF burden (number of episodes multiplied by their duration in hours) experienced following the procedure. Success was defined as having an AF burden of less than 0.5% (3.6 hours a month) without the use of antiarrhythmics.

The electrophysiologic study involved in the procedures revealed that 72 PVs (average of 1.7/person) had reconnected in the RF group as compared to 77 PVs in the Cryo group (average of 1.9/person). All reconnected veins were successfully isolated. However, to do so required the application of RF energy in 9 PVs in the Cryo group. At the end of a 3-month blanking period, 63% of patients in the RF group and 49% of those in the Cryo group met the criterion of having an AF burden less than 0.5%. Corresponding numbers at the end of the 12-month following were 58% and 43%.

However, when taking into account that some patients in the Cryo group needed RF ablation, the numbers become a little different with those patients receiving Cryo only having a success rate of 38% as compared to 53% in the group receiving RF ablation only, or Cryo plus added RF. At the end of follow-up, 26% of patients (10 in the Cryo group and 11 in the RF group) required antiarrhythmic therapy, whilst 19 patients underwent a third ablation. No complications were observed in the RF group but 3 patients in the Cryo group experienced transient phrenic nerve paralysis. The authors of the report conclude that RF ablation is superior to Cryo when it comes to "redo" procedures.

Pokushalov, E, et al. Cryoballoon versus radiofrequency for pulmonary vein re-isolation after a failed initial ablation procedure in patients with paroxysmal atrial fibrillation. Journal of Cardiovascular Electrophysiology, Vol. 24, March 2013, pp. 274-79

Editor's comment: It is interesting that the American/Russian team defines success as having an afib burden of less than 0.5%. Most afibbers can live with that, and characterizing failure as experiencing one post-ablation episode lasting longer than 30 seconds, as is currently the norm, does seem a bit unrealistic. This study confirms my own opinion that RF ablation is superior to Cryo, assuming equally skilled operators.