ECRG4 and rheumatic heart disease: Atrial fibrillation may also be linked to lower ECRG4 expression in other patients besides tumor patients Five suitable atrial appendage specimens from patients with rheumatic heart disease with or without atrial fibrillation were further collected clinically to investigate the expression of ECRG4 in the heart, and immunohistochemistry confirmed the downregulation of ECRG4 in the atrial appendage of patients with atrial fibrillation (30).