Systolic Bundle Branch Block, Left

This 2x2 randomized crossover feasibility study will evaluate the therapeutic value of adding pacing from the left ventricular lead to Left Bundle Branch Area Pacing (LBBAP) using a cardiac resynchronization therapy defibrillator (CRT-D). This combined therapy is known as Left Bundle Branch Optimized Cardiac Resynchronization Therapy (LOT-CRT) and will be compared to LBBAP therapy over sequential 6-month periods in CRT-indicated patients with LBBB. Primary and secondary outcomes are echocardiographic changes. Exploratory assessments will include NT-proBNP and subject-reported quality of life (KCCQ). An observational treatment arm will include subjects who have not been randomized due to unsuccessful implant for real-world observational analysis

This 2x2 randomized crossover feasibility study will evaluate the therapeutic value of adding pacing from the left ventricular lead to Left Bundle Branch Area Pacing (LBBAP) using a cardiac resynchronization therapy defibrillator (CRT-D). This combined therapy is known as Left Bundle Branch Optimized Cardiac Resynchronization Therapy (LOT-CRT) and will be compared to LBBAP therapy over sequential 6-month periods in CRT-indicated patients with LBBB. Primary and secondary outcomes are echocardiographic changes. Exploratory assessments will include NT-proBNP and subject-reported quality of life (KCCQ).