Evaluation of A Clinical Diagnostic Test for CRDS

Cohort 1: Calcium Release Deficiency Syndrome (CRDS) Cases Inclusion criteria: • Presence of an RyR2 variant confirmed to be loss-of-function on in vitro testing Exclusion criteria: • Unable to provide informed consent Cohort 2: Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) Cases Inclusion criteria: * Satisfy a clinical phenotype consistent with the Expert Consensus Statement * Presence of a confirmed or presumed pathogenic gain-of-function RyR2 variant OR homozygous or compound heterozygous for likely pathogenic/pathogenic CASQ2 variants Exclusion criteria: * Unable to provide informed consent * Use of a QT prolonging medication, aside from flecainide, at the time of the burst pacing maneuvers Cohort 3: Survivors of Unexplained Cardiac Arrest (UCA) Inclusion criteria: * Cardiac arrest requiring cardioversion or defibrillation that remains unexplained following an ECG, echocardiogram, coronary assessment, cardiac MRI, and exercise treadmill test * Undergone genetic testing that includes screening of RyR2\* Exclusion criteria: * Unable to provide informed consent * Use of a QT prolonging medication at the time of the burst pacing maneuvers * Among survivors of UCA that possess a rare RyR2 variant in the absence of a CPVT phenotype, in vitro functional testing will be performed in order to confirm it is not loss- or gain-of-function (and will be arranged through the laboratory of Dr. Wayne Chen at the University of Calgary). Cohort 4: SVT controls Inclusion criteria: • Undergoing an invasive electrophysiology study Exclusion criteria: * Ventricular cardiomyopathy * Ventricular pre-excitation * Long QT syndrome * Use of a QT prolonging medication at the time of the EP study * Use of a Class I or Class III anti-arrhythmic drug at the time of the EP study * Known obstructive coronary artery disease (existing coronary stenosis \>50%) * Unable to provide informed consent