Registry of Unexplained Cardiac Arrest

Inclusion Criteria: * Cardiac arrest requiring cardioversion or defibrillation. * Syncope with documented polymorphic ventricular tachycardia felt to be responsible for the index event. * First degree relative of an index case of UCA undergoing clinical testing. * First degree relative of a family member with UCA or sudden death before age 35 with a negative autopsy for cause of death, presumed arrhythmic. * First degree relative of a family member with UCA or sudden death with objective evidence of primary electrical disease, such as a diagnostic electrocardiogram (ECG), exercise test, drug infusion, or genetic testing. Exclusion Criteria: * Coronary artery disease (stenosis \> 50%) * Reduced left ventricular function (left ventricular ejection fraction \[LVEF\] \< 50%) * Event managed without an implantable cardioverter defibrillator \[ICD\] (for follow-up portion) * Unwilling or unable to provide clinical follow-up (for follow-up portion) * Comorbidity making survival of \> 1 year unlikely * Persistent resting QTc \> 460 msec for males and 480 msec for females * Reversible cause of cardiac arrest such as marked hypokalemia (\< 2.8 mmol/l) or drug overdose sufficient in gravity without other cause to explain the cardiac arrest * Hemodynamically stable sustained monomorphic ventricular tachycardia with a QRS morphology consistent with recognized forms of idiopathic ventricular tachycardia (outflow tract or apical septal) * Brugada's sign with e2 mm ST elevation in V1 and/…