RYR2 and catecholaminergic polymorphic ventricular tachycardia: In contrast to experimental evidence implicating a Ca2+ clock involving RyR2 in pacemaker activity (see section on Features of Ca2+ homeostasis in sino-atrial and atrial cells have implications for rhythm abnormalities), CPVT is associated with high incidences of SAN dysrhythmia in the form of reduced SAN automaticity resulting in basal bradycardia, sinus pauses, and impaired chronotropic responses to β-adrenergic stimulation (Leenhardt et al., 1995; Sumitomo et al., 2003; Postma et al., 2005; Katz et al., 2009).