CARDIO-TTRansform: A Study to Evaluate the Efficacy and Safety of Eplontersen (Formerly Known as ION-682884, IONIS-TTR-LRx and AKCEA-TTR-LRx) in Participants With Transthyretin-Mediated Amyloid Cardiomyopathy (ATTR CM)

Inclusion Criteria: * Females must be non-pregnant and non-lactating, and either surgically sterile or post-menopausal or abstinent. If engaged in sexual relations of child-bearing potential, agree to use 1 highly effective contraceptive method * Males must be surgically sterile or, abstinent or, if engaged in sexual relations with a woman of child-bearing potential, the participant or the participant's non-pregnant female partner must be using a highly effective contraceptive method * Amyloid deposits in cardiac or non-cardiac tissue confirmed by Congo Red (or equivalent) staining OR technetium scintigraphy (99mTc -3,3-diphosphono-1,2- propanodicarboxylic acid \[DPD-Tc\], 99m Tc-pyrophosphate \[PYP-Tc\], or 99m Tc-hydroxymethylene-diphosphonate \[HMDP-Tc\]) with Grade 2 or 3 cardiac uptake in the absence of abnormal light chains ratio, centrally confirmed * End-diastolic interventricular septum thickness of \> 12 millimeters (mm) on Screening echocardiogram * New York Heart Association (NYHA) class I-III Exclusion Criteria: * Acute coronary syndrome, unstable angina, stroke, transient ischemic attack (TIA), coronary revascularization, cardiac device implantation, cardiac valve repair, or major surgery within 3 months of Screening * Cardiomyopathy not primarily caused by ATTR-CM, for example, cardiomyopathy due to hypertension, valvular heart disease, or ischemic heart disease * Monoclonal gammopathy of undetermined significance (MGUS) and/or alterations in immunoglobulin …