Background Previous studies reported that ablation of low‐voltage areas ( LVA s) after pulmonary vein isolation ( PVI ) improves the success rate in persistent atrial fibrillation (Per AF ) patients with LVA s. However, the need for LVA ablation in addition to the posterior left atrial isolation, Box isolation ( BOXI ), for Per AF is unclear. We evaluated the effects of LVA ablation after BOXI for Per AF with LVA s. Methods In 115 patients with Per AF (75 longstanding Per AF ), LA voltage maps were created during sinus rhythm after PVI . Subsequently, BOXI was performed. In 61 patients without LVA s (<0.5 mV ), BOXI alone was performed. Fifty‐four patients with LVA s were randomly assigned to BOXI plus LVA ablation (33 patients) or BOXI alone (21 patients). Results The rate of AF termination or cardioversion after BOXI was significantly higher than that after PVI (100% vs 88%, P < 0.001). The inducibility of atrial tachyarrhythmia after BOXI was significantly lower than that after PVI (27% vs 100%, P < 0.001). During 24 ± 9 months of follow‐up after a single procedure, atrial tachyarrhythmia‐free rate in the patients with LVA s, was significantly lower than that without LVA s (65% vs 82%, P = 0.043). However, the success rate was not significantly different between the BOXI plus LVA ablation group and the BOXI alone group of patients with LVA s (67% vs 62%, P = 0.722). Conclusion BOXI facilitates AF termination and its non‐inducibility. Among patients with Per AF , BOXI alone may be adequate in cases without LVA s. Although cases with LVA s have higher risk of AF recurrence, additional LVA ablation does not improve the outcomes much.

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Background: Additional benefits of posterior left atrial (LA) box isolation (BOXI) over pulmonary vein isolation (PVI) in persistent atrial fibrillation (perAF) have been reported, but the mechanism is still unclear. We evaluated the effects of BOXI on rotors and multiple wavelets in the whole LA. Methods and Results: Twenty patients with perAF (including 12 cases of longstanding perAF) underwent PVI. Real-time phase mapping (ExTRa Mapping) was performed in the whole LA during AF. Subsequently, BOXI was added and re-ExTRa Mapping was performed again at the same site. The nonpassively activated ratio (%NP), the ratio of the form of rotors and multiple wavelets to the recording time, was compared before and after BOXI. After BOXI, the %NP significantly decreased in the anterior wall (from 53±22% to 39±23%, P=0.010), inferior wall (from 51±16% to 34±19%, P=0.001), and LA appendage (from 23±27% to 16±19%, P=0.049). However, there were no significant differences in the septum (49±19% vs. 49±18%, P=0.562) or lateral wall (41±19% vs. 38±15%, P=0.526). Conclusions: BOXI not only reduced the critical mass for maintenance of AF, but also decreased the rotors and multiple wavelets in the anterior wall, inferior wall and LA appendage during perAF.