Reduction in muscle mass of the left atrial wall is associated with duration of atrial fibrillation

Introduction The left atrium (LA) plays a central role in the occurrence and maintenance, as well as the recurrence, of atrial fibrillation (AF). Although many studies have demonstrated that LA dilatation is associated with AF, the histological assessment remains insufficient. Methods LA wall samples obtained during cardiac surgery (N = 60) were retrospectively analyzed. The samples were processed by layer and area analysis using Masson’s trichrome staining. Results The thickness of the LA wall was 1257–6905 μm. Layer analysis demonstrated that the wall thickness was not associated with the LA volume. Multivariable linear regression analysis revealed that the LA thinning was associated with persistent AF. Moreover, LA wall thickness was well correlated with muscle layer thickness. The patients who had AF for one year or more showed a significant reduction in muscle content compared to those with AF for less than one year. Among the 36 patients who underwent concomitant Maze procedure, nine had presence of AF one year after surgery. Age, AF duration, and reduction in muscle area were associated with AF persistence after the Maze procedure. Conclusion AF was the only factor associated with a reduction in cardiac muscle mass in the LA wall. Chronic AF of more than one year’s duration enhanced the risk of reduction in LA muscle content.