NRTN and atrial fibrillation: There were no significant differences in the percentage of immunopositive cells for NRTN in both AF and NP tissues between the early stage (AF: 14.7 ± 2.7%, NP: 17.4 ± 3.5%) and advanced degenerate stage (AF: 18.0 ± 3.5%, NP: 21.0 ± 3.7%) (Figure 5a).