Effectiveness of cryoballoon isolation

ROTTERDAM, THE NETHERLANDS. When the pulmonary vein isolation (PVI) procedure was first introduced it was common practice to place the lesion rings just inside the pulmonary veins. However, when it became apparent that this approach had an inherently high risk of pulmonary vein stenosis, the lesions rings were moved so as to be placed in the left atrium itself either very close to the edge of the junction between the veins and the atrium (antrum PVI) or somewhat further out guided by CARTO or similar mapping. This approach, for all intents and purposes, eliminated stenosis, but did made it more difficult to ensure that the rings were complete and totally eliminated electrical conduction between the veins and the atrium.

In parallel with this development EP researchers were also working on an entirely different approach to avoiding stenosis, namely that of cryoablation. Pulmonary vein isolation using cryoablation is a procedure very similar to the standard PVI using radiofrequency energy for lesion creation except that it uses a nitrogen-cooled (-90oC) catheter rather than an electrically-heated catheter. Cryoablation is potentially safer than RF ablation in that the risk of pulmonary vein stenosis and esophageal injury is pretty well non-existent. The procedure also has the advantage that, since no pain is felt during lesion creation, it does not require conscious sedation or anesthesia.

A group of electrophysiologists from the Erasmus Medical Center in Holland now report on their experience using a cryoballoon catheter (Arctic Front, Cryocath, Quebec, Canada) and an 8-mm cryo-catheter (Freezor Max) also developed by Cryocath. Their clinical trial involved 141 afibbers with paroxysmal AF. Average age of the patients was 56 years, 29% were women and only 5% had structural heart disease, so this was essentially a group of lone afibbers, although 19% did have hypertension.

Pulmonary vein isolation was achieved in one procedure in 138 patients. In 33 patients a 23-mm balloon catheter was used, in 99 cases a 28-mm catheter was employed, and in 7 cases both balloons were used. In addition, the Freezor Max catheter was used to complete the PVI in 56 patients. The average (mean) procedure time was 3 hours and 27 minutes and mean fluoroscopy time was 50 minutes.

Eight patients (5.7%) experienced pericardial effusion (an abnormal collection of fluid inside the sac that covers the heart) and 4 patients (2.8%) experienced right phrenic nerve paralysis. All adverse events were either dealt with or resolved on their own. Patients were followed up for an average of 457 days via daily event recording, 24-hour Holter recordings and self-reporting of afib burden (number of episodes times their duration for a specified period of time). The researchers considered the first 90 days following the procedure to be a blanking period and afib episodes occurring during this time were not included in the evaluation of ultimate success rates. Thus, the actual follow-up time was one year.

After the first procedure, 49% of the patients were afib-free without the use of antiarrhythmics. Twenty-four (17%) of the patients still on antiarrhythmics underwent a second procedure using the same equipment and protocol as used in the first procedure. The success rate for this second procedure was 54%. Thus, ultimately 58% of patients were afib-free without antiarrhythmics after an average of 1.2 procedures (20% repeat rate). The remaining 42% continued on antiarrhythmics with a much reduced afib burden. The researchers made the interesting comment that a recurrence in the first 3 months is highly predictive for recurrence after 3 months, whereas the absence of events in the first 3 months is highly indicative for a low recurrence rate. The long-term success rate was 86% in the group with no recurrence during the first 3 months versus only 41% in the group with recurrence during the blanking period.

Van Belle, Y, et al. One year follow-up after cryoballoon isolation of the pulmonary veins in patients with paroxysmal atrial fibrillation. Europace, Vol. 10, 2008, pp. 1271-76

Editorís comment: The single procedure complete success rate for this trial of cryoablation was 49%. This compares well with the 50% observed for 15 top-ranked RF ablation centers in LAF Survey 15. However, the final success rate of 58% after an average of 1.2 procedures is somewhat lower than that observed for 15 top-ranked RF institutions (65%) and significantly lower than that observed for the two top-ranked RF centers (72%). Here is should also be kept in mind that the patient population in the cryoablation trial consisted entirely of paroxysmal afibbers who are usually significantly easier to treat successfully than are those with persistent or permanent afib. It is of interest to note that the Rotterdam researchers found that recurrence of afib during the first 3 months following the procedure is a bad omen. In our September 2005 Ablation/Maze Survey (LAFS-9) we observed that the success rate among ablated afibbers who had no recurrent episodes during the first 3 months was 63% versus 37% for those who did have recurrences during the first 3 months.