Ablation for Paroxysmal Atrial Fibrillation

Posted by • June 10th, 2016

2016-06-03_12-16-42According to a 2012 expert consensus statement, catheter ablation of drug-refractory paroxysmal atrial fibrillation is a class I level A indication, and pulmonary-vein isolation is the standard approach. Kuck et al. conducted a randomized trial to compare the performance of the rather complex yet well-established approach of radiofrequency ablation with that of the apparently simpler approach of cryoballoon ablation in a larger population of patients with paroxysmal atrial fibrillation.
Over 700 patients with drug-refractory paroxysmal atrial fibrillation were randomly assigned to cryoballoon or radiofrequency ablation. Cryoballoon ablation was noninferior to radiofrequency for the composite of recurrent atrial arrhythmia, use of antiarrhythmic drugs, or repeat ablation. A new Original Article summarizes.

Clinical Pearl

• How do the two commonly used ablation techniques differ?

The two most frequently used ablation technologies for pulmonary-vein isolation differ in the energy source and mode of application. The most common method is the use of radiofrequency current applied in a point-by-point mode, which leads to cellular necrosis by tissue heating; the other method is the use of cryogenic energy applied with a balloon in a single-step mode, which leads to necrosis by freezing.

Figure 1. Catheter Ablation Methods.

Clinical Pearl

• What are the relative advantages of each of these two ablation techniques?

Radiofrequency ablation for atrial fibrillation requires only limited use of fluoroscopy, because catheter guidance is achieved with the use of an electroanatomical mapping system, but the approach demands extensive training. The complexity of radiofrequency ablation technology has restricted ablation therapy for atrial fibrillation to a few specialized centers and has limited the availability of ablation therapy. Cryoablation for atrial fibrillation requires more extensive fluoroscopic guidance to position the balloon catheter at the pulmonary veins. The cryoballoon was developed to create a circular lesion around each pulmonary vein in a relatively simple manner.

Morning Report Questions

Q: Is cryoballoon ablation as effective as radiofrequency ablation for the treatment of paroxysmal atrial fibrillation?

A: In the study by Kuck et al., cryoballoon ablation was found to be noninferior to radiofrequency ablation with regard to the primary efficacy end point, and superiority was not achieved in either group. The primary efficacy end point in a time-to-event analysis was the first documented clinical failure (recurrence of atrial fibrillation, occurrence of atrial flutter or atrial tachycardia, use of antiarrythmic drugs, or repeat ablation,) following a 90 day period after the index ablation. In the modified intention-to-treat analysis, after the 90-day blanking period, the primary efficacy end point occurred in 138 patients in the cryoballoon group and in 143 patients in the radiofrequency group (1-year Kaplan–Meier event-rate estimates, 34.6% and 35.9%, respectively; hazard ratio, 0.96; 95% confidence interval [CI], 0.76 to 1.22; P<0.001 for noninferiority). In the per-protocol analysis, the primary efficacy end point occurred in 118 patients in the cryoballoon group and in 131 patients in the radiofrequency group (1-year Kaplan–Meier event-rate estimates, 31.9% and 35.0%, respectively; hazard ratio, 0.91; 95% CI, 0.71 to 1.17; P<0.001 for noninferiority). A prespecified superiority test performed for the primary efficacy end point did not indicate a significant difference between the treatment groups (P=0.74).

Table 2. Efficacy End Points.

Figure 2. Event-free Survival for the Primary Efficacy and Safety End Points in the Modified Intention-to-Treat Cohort.

Q: In the study by Kuck et al. what was the most common safety event in each of the two study groups?

A: Phrenic-nerve injury was the most common safety event in the cryoballoon group, although the 2.7% rate in the trial was substantially lower than the 13.5% rate reported in the Sustained Treatment of Paroxysmal Atrial Fibrillation (STOP AF) trial. The most common safety events in the radiofrequency group were groin-site complications, which were unusually frequent in this trial (4.3%). Serious treatment-related adverse events of atrial arrhythmia occurred in 2.7% of the patients in the radiofrequency group and in 0.8% of the patients in the cryoballoon group (P=0.09). There was no significant difference in the primary safety end point (a composite of death from any cause, stroke or transient ischemic attack from any cause, and serious adverse events) between the radiofrequency group and the cryoballoon group.

Table 3. Safety End Points.

One Response to “Ablation for Paroxysmal Atrial Fibrillation”

  1. Sacha Salzberg says:

    There is a third means of achieving pulmonary vein isolation. Namely thoracoscopic ablation is a technique commonly used all over the world. Bilateral pulmonary vein isolation can be achieved with radiofrequency clamps epicardially in a minimally invasive fashion. Data on this have been published in Circulation in 2012 with the FAST trial, where superb effectivity was demonstrated with the thoracoscopic approach. But in addition to PVI – it appears that epicardial LAA resection of clipping also leads to silencing LAA generated AF – which in turn may explain why thoracoscopic ablations fare so well when compared to catheter based techniques.