A Study of Olezarsen (ISIS 678354) in Participants With Hypertriglyceridemia and Atherosclerotic Cardiovascular Disease, or With Severe Hypertriglyceridemia

Inclusion Criteria: * Participants must fall into 1 of the following groups (a or b): a. Hypertriglyceridemia with fasting TG ≥200 mg/dL (2.26 millimoles per liter \[mmol/L\]) and \<500 mg/dL (5.65 mmol/L) with either * Clinical diagnosis of atherosclerotic cardiovascular disease (ASCVD) or * At increased risk for ASCVD b. Severe hypertriglyceridemia with fasting TG ≥500 mg/dL (5.65 mmol/L) * Participants should be on standard of care (SOC) lipid-lowering medications per local guidelines. Lipid-lowering medications should be optimized and stabilized for at least 4 weeks prior to Screening to minimize changes in these medications during the study. Exclusion Criteria: * Hemoglobin A1c (HbA1c) ≥ 9.5% at Screening * Alanine aminotransferase or aspartate aminotransferase \> 3.0 × upper limit of normal * Total bilirubin \> 1.5 upper limit of normal unless due to Gilbert's syndrome * Estimated GFR \< 30 mL/min/1.73 m\^2 NOTE: Other Inclusion/Exclusion criteria may apply.