The cohort defined above will be analyzed using a nested case-control approach, where cases are defined as a first diagnosis of ventricular tachyarrhythmia (VT) or sudden cardiac death (SCD) any time after cohort entry. For each case, up to 30 controls will be randomly selected among the cohort members in the risk sets defined by the case, after matching on age, sex, date of cohort entry (±1 year), and duration of follow-up. Matching on duration of follow-up (i.e., our best estimate of duration of the disease) will serve as a proxy to control for the potential for confounding by progression and severity of Parkinson's disease.