ARTN and atrial fibrillation: The percentage of ARTN-immunopositive cells in AF (79.9 ± 2.7%) and NP (86.0 ± 2.2%) tissues in the advanced degenerated stage was significantly higher than those in the early degenerated stage (AF: 56.9 ± 4.6%, p < 0.05; NP: 69.2 ± 3.6%, p < 0.01, Figure 7a).