Discussion
The present study investigated the details after catheter ablation in patients with non-paroxysmal AF, particularly those who underwent LAPW cryoballoon ablation including the LA roof. The main results showed that cryoballoon ablation of the LAPW was not associated with AT recurrence after the ablation procedure, but LA roof-dependent AT was observed in several patients (1.5%). Moreover, clinical outcomes were improved after the ablation procedure compared with the strategy without LAPW ablation, especially regarding the recurrence of the persistent type of AF. The details of recurrence patterns, including the type of AT, and the durability of lesions created in the index ablation procedure, were also investigated in this single-center large cohort study.
PVI has been established as the gold standard for treating AF, and cryoballoon ablation has emerged as a novel ablation method instead of the conventional method utilizing RF energy7; however, its efficacy may be limited, especially in patients with non-paroxysmal AF. Various therapeutic approaches have been investigated for AF catheter ablation; linear ablation, such as LA roof line and MI line, is one such approach. In particular, linear ablation that targets the LAPW, including isolation of the LA roof line and LAPW bottom line, has been a prominent focus.2 Recently, it has been demonstrated that a cryoballoon could be utilized for linear ablation at the LAPW, and this additional ablation could generate a broader isolated area after PVI with a cryoballoon.4,8,9 Complete conduction block at the LA roof line was reportedly achieved in 81.0%–95.0% of ablations with RF energy10,11 and in 88.0%–99.8% with a cryoballoon.4,8 Regarding the chronic status of the lesions, the reported durability of the LA roof line was 37.5%–72.0% with RF energy12,13 and 74.5% with a cryoballoon.6 Indeed, several reports have shown additional LAPW ablation results in better clinical outcomes,8,14 but the adjunctive value of LAPW ablation in addition to PVI is controversial.15 In our study, the LA roof line was successfully ablated with a cryoballoon in 97.0% of patients, of whom 72.0% had confirmed durable lesions, which is consistent with previous reports. Moreover, further analysis regarding the recurrence type in this study revealed that LAPW ablation in addition to PVI could reduce the persistent type of AF recurrence, which seemed to be clinically important. A prior examination investigated the atrial substrate size by utilizing the parameter of conduction velocity, refractory period, and LA body area.16 Considering the mechanism of reduced persistence of AF after ablation based on the reported theory, cryoballoon ablation of the LA roof might be effective in reducing the atrial substrate size because it could produce a broader scar area, as previously reported.4,6,9 In this regard, cryoballoon ablation might be preferable to a conventional RF method for creating LA roof line. AF persistence seems to depend on the site of AF drivers, and it might be an important factor where AF drivers exist; however, findings regarding AF drivers were not examined in the present study. Moreover, A wave was significantly lower in the patients who underwent cryoballoon ablation of the LAPW in this study, although that of those who underwent cryoballoon ablation of the LAPW seems compatible according to the previous study17. Further studies might be required for assessing atrial function after the ablation more precisely, and selecting candidates who should undergo cryoballoon ablation of the LAPW.
One of the reasons for hesitation in performing linear ablation was the possibility of iatrogenic AT occurrence after the ablation procedure. After PVI, including both RF energy and cryoballoon ablation, AT recurrence was observed in approximately 10% of patients according to previous reports.18-20 In several studies that compared the prevalence of AT recurrence between patients who underwent PVI with RF energy and those who underwent PVI with a cryoballoon, the AT recurrence rate tended to be lower in those who underwent PVI with a cryoballoon.18 Among recurrent ATs, perimitral AT was reportedly the most frequently observed, accounting for approximately 30% of AT recurrences in previous investigations.19,20 Regarding linear ablation with RF energy, the recurrence of AT originating from the LA was reported to be 4% in patients.21 Data regarding the prevalence of AT recurrence after linear ablation with a cryoballoon are limited. Aryana et al. investigated cryoballoon ablation of the LAPW and demonstrated that approximately 20% of patients experienced AT recurrence regardless of whether cryoballoon ablation of the LAPW was performed in addition to PVI; however, detailed descriptions regarding the type of recurrent ATs are lacking.8 In our study, 7.4% (10/135) of the patients who underwent cryoballoon ablation of the LAPW had AT recurrence, which is comparable with previous reports, including RF ablation. We demonstrated that perimitral AT was the most frequent type of recurrent AT, accounting for half of the identified recurrent ATs in our study cohort. LA roof-dependent AT was confirmed in only two patients, who both underwent cryoballoon ablation for LAPW in the index ablation. However, considering previous reports in which the prevalence of LA roof-dependent AT recurrence was 1%–2% after PVI with a cryoballoon,19,20 the recurrence rate of the LA roof-dependent AT in the present study might not be high. The high durability of the lesions created at the LAPW might contribute to the low prevalence of LA roof-dependent AT recurrence.
Our study had a few limitations. First, this was a single-center, non-randomized retrospective study. Therefore, the results regarding additional cryoballoon ablation of the LAPW should be carefully interpreted, although there were no significant differences in patient characteristics such as left atrial diameter (LAD) or the existence of left common pulmonary vein (LCPV) or right middle pulmonary vein (RMPV) between the patients who underwent cryoballoon ablation of the LAPW and those who did not. Finally, the use of AADs after the index ablation was also different among study patients; thus, clinical follow-up data requires prudent interpretations. A randomized multicenter study with a fixed protocol is necessary to confirm the efficacy and impact of LAPW ablation with a cryoballoon. Nonetheless, we presented detailed data in terms of acute and long-term success rates and clinical outcomes after ablation, including the type of recurrence. We consider that these findings will contribute to further examinations regarding cryoballoon ablation of the LAPW in the future.