Cryoballoon ablation as first-line therapy of paroxysmal atrial fibrillation: dusk of global warming and the dawn of a new ice age era?

This editorial refers to ‘Isolating the pulmonary veins as first-line therapy in patients with lone paroxysmal atrial fibrillation using the Cryoballoon’ by M. Namdar et al., on page 197

The introduction of catheter ablation for the treatment of supraventricular arrhythmias in the early 1980s initially with the delivery of intra-cardiac DC shocks and finally in 1987 with the introduction of radiofrequency energy changed forever the management of supraventricular tachycardias.^1–3 Despite the safety, reproducibility, and high efficacy rates, catheter ablation of supraventricular tachycardias is still not considered first-line therapy. Similarly, despite many attempts with different energy sources radiofrequency ablation remains the gold standard.

The proposal for a catheter-based approach in the mid 1990s for the treatment of atrial fibrillation was met with significant scepticism. Initial attempts using extensive lines trying to reproduce the Cox-Maze approach were associated with mediocre results and untenable procedure and fluoroscopic times.^4,5 Nonetheless perseverance and a better understanding of the mechanisms of atrial fibrillation as well as the recognition, both experimentally and clinically, of the importance of the left atrium and in particular of the role of the pulmonary veins in the initiation and possibly in the maintenance of atrial fibrillation paved the way to the current catheter-based approaches for atrial fibrillation treatment.⁶ In 1998, the Bordeaux group provided the final piece of the puzzle that changed the management of atrial fibrillation and spearheaded the current enthusiasm.⁷

The bulk of evidence collected in the past decade related with the efficacy of radiofrequency catheter ablation in patients with paroxysmal and persistent atrial fibrillation compared with antiarrhythmic drug therapy clearly favours catheter ablation.^8–10 The treatment effect based on time to first recurrence of atrial fibrillation is in the range of a 60–70% relative risk reduction in the short- to mid-term 12–24-month follow-up. It has recently become apparent that the ‘long-term’ results are not as enticing particularly in patients with persistent atrial fibrillation where recurrence can be expected in >50% by 5 years.^11,12

First-line catheter ablation for atrial fibrillation has been previously reported with significant success using radiofrequency catheter ablation and two studies will be presented in the next few months [RAAFT-2 (Radiofrequency Ablation Atrial Fibrillation Trial-2) and MANTRA-PAF (Medical ANtiarrhythmic Treatment or Radiofrequency Ablation in Paroxysmal Atrial Fibrillation)] with >300 patients randomized to either strategy.^13,14 The results of these two trials are being anxiously awaited. Current trends indicate that first-line radiofrequency ablation is being offered more frequently in younger patients and in up to 17% in a recent single-centre report.¹⁵

In the present issue of Europace, Namdar et al.¹⁶ present their preliminary results reporting the use of cryoballoon for pulmonary vein isolation (PVI) as first-line therapy in younger patients with paroxysmal atrial fibrillation. This was a non-randomized single-centre experience involving 18 patients with a mean age of 44 years. By and large this was a relatively healthy population with a preserved left ventricular function and mildly dilated left atrium (39 ± 4 mm). A mean of 2.4 cryoballoon applications were needed and acute success defined as PVI was reported in 97%. In the remaining 3% (two PVIs in two patients) radiofrequency ablation was needed to achieve isolation. Success defined as freedom of recurrence of symptomatic atrial fibrillation was reported in 89% after a mean follow-up period of 14 ± 9 months.

This is yet another attempt to justify early intervention and first-line therapy of atrial fibrillation in this case using a newer technique such as cryoballoon ablation. The study has several limitations given by the very small sample size and single-centre experience. Of note the success rate in this group was markedly superior to that reported by the STOP-AF (Sustained Treatment of Paroxysmal-Atrial Fibrillation) investigators using the same technique.¹⁷ Several factors may account for this observation, such as the small sample size and the younger population opening room for speculation regarding the fact that early intervention (younger patients, earlier stage of atrial fibrillation) may have a higher success rate. Recently, Leong-Sit et al.¹⁸ have also suggested that PVI in patients younger than 45 years seems to have a better efficacy.

A very significant limitation is the definition of success. Unfortunately, this study did not abide by the 2007 Heart Rhythm Society ‘Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation’ recommendations on the definition of a valid primary outcome that should include both symptomatic as well as asymptomatic recurrences of atrial fibrillation and atrial tachycardias and flutter.¹⁹ Furthermore, to be able to identify the above-mentioned primary outcome a very thorough monitoring strategy using preferably trans-telephonic monitoring systems is needed. The current study barely monitored these patients with a single 24h Holter during the follow-up period, seriously limiting the ability to identify recurrences of atrial fibrillation and other tachyarrhythmias known to be observed at follow-up.

Notwithstanding the authors are to be congratulated for pioneering the use of cryoballon ablation as a first-line strategy of paroxysmal atrial fibrillation. Whether cryoballoon ablation will withstand the current ‘global warming’ and not melt down, or whether we are at the verge of a new ‘ice age’ can only be answered by time and the proper conduct of randomized clinical trials.

Conflict of interest: C.A.M. is currently conducting research sponsored by Biosense Webster, St. Jude Medical, and Boston Scientific, and is a member of the speakers' bureau for Biotronik, Boehringer Ingelheim, Sanofi Aventis, and Merck.

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Author notes