Optimization of Cardiac Resynchronization Therapy by Non-Invasive Imaging of Cardiac Electrophysiology

This study uses a specialized heart imaging technique (called cardiac mapping from MRI data) to find the most effective programming settings for cardiac resynchronization therapy (CRT) devices — pacemaker-like devices used to improve the pumping function of the heart in people with heart failure and electrical conduction problems. **You may be eligible if...** - You have had a CRT device implanted (CRT-D or CRT-P) that includes the SyncAV programming feature - You have left bundle branch block (a specific electrical problem in the heart) - Your heart's electrical conduction time (PQ interval) was 250 ms or less before implantation - You are able to safely have a cardiac MRI **You may NOT be eligible if...** - You have high-grade heart block requiring continuous pacing - You have any contraindication to MRI (claustrophobia, certain implants, etc.) - Your heart failure is at a very advanced stage (NYHA class IV) or you are currently unstable - You are pregnant or a woman who could become pregnant - Your life expectancy is less than 1 year - You have a substance use disorder Talk to your doctor to see if this trial is right for you.