SCN5A and paroxysmal familial ventricular fibrillation: Furthermore, loss-of-function Nav1.5 mutations have been described in patients with idiopathic ventricular fibrillation (IVF), an uncommon and lethal condition which presents itself as syncope or sudden cardiac death in young people with normal hearts and without electrophysiological manifestations of inherited arrhythmogenic syndromes [5-7].