HCN4 and atrial fibrillation: Accordingly, several studies have linked genetic variants in genes encoding sodium (SCN5A, INa) [43], potassium (KCND3,Ito; KCNA5, IKur; KCNN2, ISK2; KCNN3, ISK3) [44,45,46,47], calcium (CACNB2 and CACNA2D4, ICaL) [48], and HCN4 (If) [49] channels with AF.