Among them, 8 studies evaluated the association between baseline atrial natriuretic peptide (ANP) levels and AF recurrence after CA, 37 studies evaluated for brain natriuretic peptide (BNP), 25 studies evaluated for N-terminal pro-BNP (NT-proBNP), and 4 studies evaluated for midregional N-terminal pro-ANP (MR-proANP). The gene discussed is NPPA; the disease is atrial fibrillation.