HCN4 and sick sinus syndrome: Pathogenic HCN4 alterations have been associated with a broad spectrum of conditions, mainly sick sinus syndrome and Brugada syndrome, but also with LVNC, sinus bradycardia, sinus tachycardia, atrial fibrillation, atrioventricular block, idiopathic ventricular tachycardia, myocardial infraction, sudden infant death syndrome, ARVC, dilation of the aorta and chronotropic incompetence [35,36].