Prevalence of the EC
Previous studies have reported an inconsistent prevalence of an EC between right-sided PV and the RA in patients undergoing PVI: 18% by Yoshida et al. and 51% by Hanaki et al.6,12 The prevalence of an EC in the current study fell between that of those studies of Japanese patients, at 31%. In contrast, Barrio-Lopez et al. reported a much lower prevalence (6.8%).7 This may be due to differences in races and the method of ECs verification. They confirmed the presence of ECs after PV antrum ablation, which might have led to underestimation because of the elimination of ECs. Contrary to their study, three other studies, including the current study, evaluated ECs before PV antrum ablation using the LA activation map.
As for the LA activation map, the mean number of LA mapping points in the current study was much larger than that in the reports by Yoshida and Hanaki (2532 vs. 679 vs. 1479, respectively). Further, those other reports did not mention specific methods for visualizing the activation pattern of LA in detail. We confirmed the existence of the EC before ablation with Ripple mapping and Coherent mapping, which are useful for atrial tachycardia and other reentrant tachycardia ablations as well as for detecting the presence of ECs by visualizing activation patterns.
In accordance with previous reports, most EC sites were located anterior to the carina segment of the right-sided PV. However, we must recognize that the EC is composed of multiple myofibers.9 The EC site was defined as the earliest activation site near the right-sided PV except for Bachman bundle. However, the “EC site” in our study was only the earliest conduction site on the PV side of the myofibers. In previous anatomical studies, the muscle fibers were also widely attached elsewhere in the craniocaudal direction and transverse to the epicardial fat of the interatrial groove.9 In Figure4A, we depict the figure of epicardial fiber connected between the RA and LA speculated in a previous study. The attachment of epicardial fibers in the LA might be a variable location that would influence PVI success.