A, Electrogram leading up to ventricular fibrillation (VF) in the genetically affected first-degree relative of proband 3 showing sinus tachycardia with stable cycle length, 2 premature ventricular complexes (PVCs), a long pause, a sinus beat, and a shorter coupled PVC, precipitating polymorphic ventricular tachycardia/VF. B, Dot plot of appropriate implantable cardioverter-defibrillator high-rate detection in second VF episode in proband 1 with RyR2-p.Q2275H variant. A indicates atrial; V, ventricular.