Histological staining
Masson’s trichrome staining (Nanjing Jiancheng Bioengineering Institute) was performed on samples from the AVN region according to the manufacturer’s instructions to assess fibrosis and delineate the initiation of the inferior region of the AV conduction system. Acetylcholinesterase (AChE) staining was also performed on adjacent sections as a secondary confirmation of the conduction system, as previously described.9