Implant procedure will be per routine percutaneous access, as is standard for pacemaker and ICDs. All subjects will receive an FDA-approved cardiac resynchronization therapy pacemaker or defibrillator device, as per standard of care outlined for the subject. In order to facilitate optimal lead placement, arterial access for levo-phase CS angiography and/or LV septal mapping to characterize site of bundle-branch block may also be performed, at the discretion of the implanting physician per his/her standard practice.