Atrial Remodeling and Lone Atrial Fibrillation. Background: We sought to investigate the role of anatomic remodeling of the atria and pulmonary veins (PVs) in the progression of lone atrial fibrillation (AF) using dual-source computed tomography (DSCT). Methods and Results: From 1,308 consecutive patients referred for an index ablation procedure for AF, we prospectively enrolled 29 consecutive patients with recently developed (<3 months) lone persistent AF (PsAF) and 23 consecutive patients with short-lasting (612 months) lone PsAF, all of whom had a history of paroxysmal AF (PAF). The control group consisted of 33 patients with lone PAF. On DSCT, the recently developed PsAF group showed more extensive atrial anatomic remodeling than the PAF group as shown by similar to 40% higher spot biatrial volume, even though the mean duration of continuous AF was only 6 weeks. In contrast, the DSCT variables in the recently developed PsAF group and the short-lasting PsAF group were comparable, despite the fact that the mean duration of continuous AF in the latter group was 8 months. Series of cross-sectional areas of the ostial 1.5 cm of PV trunks were comparable in the PAF and PsAF groups in all but 3 ostial planes. A higher spot left atrial volume was the only independent factor associated with the progression of lone PAF to PsAF (OR: 1.06, 95% CI: 1.031.09, P<0.0001) on logistic regression. Conclusions: Prominent anatomic remodeling of the atria, rather than the PVs, underlies the mechanism of recent progression of lone paroxysmal AF to the persistent variety. (J Cardiovasc Electrophysiol, Vol. 23, pp. S29-S35, November 2012)