Balloon Technologies for Atrial Fibrillation Ablation　― It Really Is a Hot Topic Now! ―

Atrial fibrillation (AF) is the most common tachyarrhythmia, associated with stroke, systemic embolism, and heart failure, leading to increased mortality. Catheter ablation is an effective therapeutic option to restore and maintain sinus rhythm in patients with AF, and it is being increasingly performed worldwide. Because most of the ectopic beats triggering AF arise from the pulmonary veins (PVs), PV isolation (PVI) is the cornerstone of AF ablation, and point-by-point radiofrequency catheter ablation (RFCA) around the PVs has been the mainstay of PVI. However, despite the development of 3D mapping systems and high-performance ablation catheters with an irrigation tip and contact force sensing technology, point-by-point RFCA remains a technically complex procedure. Thus, several balloon devices have been developed to realize simpler PVI procedure with less catheter manipulation at the target PVs.^1,2

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The cryoballoon was the first approved balloon device for PVI, and is now the most commonly used worldwide.¹ The refrigerant N₂O is delivered into the balloon where it undergoes a liquid-to-gas phase change, resulting in an inner balloon temperature of approximately −80℃. The 1st-generation device (Arctic Front^TM, Medtronic, MN, USA) became available in Europe in 2006 and was approved in the USA in 2011. A 2nd-generation device (Arctic Front Advance^TM, Medtronic) (Figure A) was approved simultaneously in Europe and the USA in 2012, and in Japan in 2014. For this cryoballoon, the refrigerant injection ports were doubled, and their positions were moved 4.5 mm more distal, which enabled more homogeneous freezing of the frontal hemisphere of the balloon. Two different diameters (23 and 28 mm) are available, although the smaller size is rarely used. Recording of PV potentials is available during freezing by a dedicated spiral mapping catheter. The acute PVI success using the 2nd-generation cryoballoon alone was reported to be 97.5–100% per PV and 90.5–100% per patient.³ Recently, 3 randomized clinical trials (RCTs) compared cryoballoon PVI vs. antiarrhythmic drug therapy as the first-line therapy of untreated AF. Cryoballoon PVI was associated with higher arrhythmia-free rates, improved quality of life, and less hospitalization without an increase in the risk of adverse events.⁴ Also, in several RCTs comparing 2nd-generation cryoballoon vs. point-by-point RFCA with contact force sensing catheter, cryoballoon PVI was associated with shorter procedure time and comparable rates of acute complications and mid- to long-term arrhythmia-free survival.² The prevalence of right-side phrenic nerve palsy has been reported to be 1.4–2.7%, although it resolved within 1 year in most cases.^3,4 Recently, a similar type of cryoballoon (PolarX^TM, Boston Scientific, MA, USA) (Figure B) was launched in Europe and Japan. The acute and long-term clinical outcomes of AF ablation using this novel cryoballoon will be evaluated in ongoing and future studies.

Figure.

Balloon devices for PVI available in Japan. (A) Arctic Front Advance^TM Cryoballoon (Medtronic, MN, USA). Image courtesy of Medtronic. (B) PolarX^TM Cryoballoon (Boston Scientific, MA, USA). Image courtesy of Boston Scientific. (C) HeartLight X3 Laser Balloon (CardioFocus, MA, USA). Image courtesy of CardioFocus. (D) Satake HotBalloon (Toray Industries, Tokyo, Japan). Images courtesy of Toray Industries.

The 1st-generation laser balloon (HeartLight, CardioFocus, MA, USA) was approved in Europe in 2011, followed by the USA in 2016 and Japan in 2017. The transparent and compliant balloon is dilated with a continuous flush of deuterium oxide and wedged to the target PV. Under real-time visualization of the PV ostium via a 2F fiberoptic endoscope inside the balloon, point-by-point laser energy applications from the central lumen of the balloon in an overlapping fashion achieve PVI. Although the total procedure time of PVI using the 1st-generation laser balloon was long, 154 min on average, the acute success rate was as high as 98.8% per PV.⁵ With the recently approved 3rd-generation laser balloon (HeartLight X3, CardioFocus) (Figure C), application of the laser energy is automated, and the total procedure time markedly reduced to ≈60 min in early reports.^6,7 The size-adjustable feature of the laser balloon, ranging from 7 to 41 mm, is attractive, enabling isolation of large PVs. On the other hand, real-time recording of PV potentials during the energy application is not available.

The Satake HotBalloon (Toray Industries, Tokyo, Japan) (Figure D) is a compliant 13F balloon catheter that is filled and inflated with contrast medium diluted with saline in 1 : 1 ratio. The balloon diameter ranges from 26 to 33 mm with an injection volume of 10–20 mL. Radiofrequency current of 1.8 MHz induces capacitive heating of the balloon, and the vibratory waves through a catheter lumen mix the fluid and homogenize the temperature inside the balloon. In a multicenter RCT comparing HotBalloon PVI and medical therapy for drug-refractory paroxysmal AF, the acute success rate of PVI was high at 98.0% per PV. The arrhythmia-free rate at 9 months was higher in the HotBalloon than in the medication group (59.0% and 4.7%, P<0.001).⁸ However, high rates of severe PV stenosis (5.2%) and persistent phrenic nerve palsy (3.7%) raised a safety concern.⁸ Because all these adverse events occurred with low (≤8 mL) injection volume, the HotBalloon was finally approved for paroxysmal AF in 2016 in Japan, with a recommendation that the injection volume should be ≥10 mL.

In this issue of the Journal, Yamasaki et al⁹ report their results of a nationwide multicenter, prospective registry of HotBalloon ablation in Japan (the HARVEST study). A total of 613 patients undergoing de novo PVI using HotBalloon for paroxysmal, persistent or long-lasting AF were enrolled from 33 centers. Although the 1-year arrhythmia-free rate with the use of class I or III antiarrhythmic drugs in nearly half of the patients was acceptable, the acute PVI success rate was only 55.6% per patient and 83.5% per PV. The acute success rate was especially low for the left superior PV (66.9%). These results were consistent with a previously reported Japanese post-marketing surveillance study.¹⁰ With regard to procedural complications, severe PV stenosis was observed in 5 of 302 patients (1.7%) who underwent follow-up CT after the procedure, and atrio-esophageal fistula occurred in 1 patient (0.2%) despite aggressive esophageal cooling with cold saline.⁹ Given the higher acute success rates in experienced centers and in patients with paroxysmal AF in the HARVEST study, refinement of the ablation protocol for each PV as well as better patient selection should improve not only the acute success rate but also the long-term clinical outcomes of this Made-in-Japan balloon device for PVI.

References

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