4.7 Study limitations
Our study had several limitations. First, the sample size was relatively small. Second, some patients underwent a prior ablation. In such cases, we could not completely discriminate between the ablation lesions and pre-existing atrial fibrosis around the PVs. Furthermore, the LGE sites might have been overestimated on the posterior wall adjacent to the vertebrae and anterior wall adjacent to the aortic cusp due to wall compression by those organs. Moreover, it might have been difficult to measure the thickness of the posterior LA wall with consistency in all patients. Thirdly, the new phase-mapping system adopted in this study may have had unknown limitations because it is widely used in Japan but not in other countries. We expect that this system will be widely used worldwide in the future. Fourth, mapping was not performed in the right atrium (RA) because of the stability of the mapping catheter and the reproducibility of the LGE-MRI assessment in the RA. Finally, no histological validation was performed in the LGE areas. LGE-MRI has a potential risk of over- and under- estimating fibrosis.