Frequency distribution analysis of activation times and regional fibrosis in murine Scn5a+/− hearts: The effects of ageing and sex

► Scn5a+/− hearts showed an electrocardiographic bundle branch block. ► Epicardial activation analysis demonstrated increased late conducting components. ► This paralleled a myocardial regional fibrosis preferentially involving the RV. ► Such changes were greatest in ageing and male Scn5a+/− hearts. ► We propose a fibrotic mechanism slowing impulse conduction in ageing Scn5a+/− hearts.