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.