PRIMARY Ancillary Substudy

Inclusion Criteria: * Patients who meet all eligibility criteria and are randomized in the parent PRIMARY trial. * For the ancillary biospecimen study, patients who are randomized to MVr in the parent trial. Exclusion Criteria: * Severe claustrophobia not controlled with sedation. * Prior adverse reaction to gadolinium administration. * Patients with an implantable subcutaneous cardioverter defibrillator and/or cardiac resynchronization therapy device with defibrillator may be excluded as they typically produce substantial artifacts on cardiac MRI making assessment very challenging. * Known allergic reaction to adhesives or hydrogels or with family history of adhesive skin allergies (for patients undergoing rhythm monitoring).