BOOST - Benefit of Frequent Optimization After Cardiac Resynchronization Therapy Device Replacement

Inclusion Criteria: * Patient underwent a CRT replacement within the last two weeks, triggered by either the elective replacement indicator (ERI)/end of life (EOL), or by receiving a CRT-D device as an upgrade from a CRT-P device. * Patient has received an FDA approved SJM CRT device as a replacement to the old CRT device within the last two weeks. * Patient has the ability to complete a 6-minute hall walk without any assistance. * Patient is willing to provide written informed consent. * Patient has the ability to independently comprehend and complete a QOL questionnaire. * Patient is geographically stable and is willing to comply with the required follow-up schedule. Exclusion Criteria: * Patient had paced/sensed AV and/or V-V delay optimization using QuickOpt before CRT replacement. * Patient had any paced/sensed AV and/or V-V delay optimization within 3 months before CRT replacement. * Patient has an ability to walk ≥ 450 meters (≥ 1476 feet) in 6 minutes. * Adequate patient's echocardiography/Doppler images will not be available. * Patient is expected to receive a heart transplant during the duration of the study. * Patient has an epicardial ventricular lead system (Active or Inactive). * Patient has limited intrinsic atrial activity (≤ 40 bpm). * Patient has persistent or permanent atrial fibrillation (AF). * Patient has 2° or 3° heart block. * Patient's life expectancy is less than 1 year. * Patient is less than 18 years old. * Patient is pregnant. * Patient is on IV inotropic agents 1 month prior to CRT replacement.