Echocardiography Guided Optimisation of Cardiac Resynchronization Therapy Late after Implantation

Heart failure patients with cardiac resynchronization therapy (CRT) devices will be investigated in a 2 stage trial investigating whether no optimization or echocardiographic CRT optimization, either at rest or on exercise, is advantageous. Optimization will occur by adjusting both the atrioventricular (AV) and ventriculo-ventricular (VV) delay of the CRT device. Stage 1 - individuals will either be randomized to no optimization or resting optimization. For this we will use the iterative method for the AV delay and the Left Ventricular Outflow Tract Velocity Time Integral (LVOT VTI) method for the VV delay. Stage 2 - individuals will either be randomized to resting optimization (as in stage 1) or optimization just on completion of a 6 minute walk test (exercise optimization). Resting optimization will be as in stage 1. On exercise (6 minute walk) we will only adjust the VV delay using the difference in time to systolic peak contraction between opposing LV segments at rest and then on exercise. Individuals will thus be optimized twice in total. At each visit they will undergo a resting echocardiogram, blood testing and measures of functional capacity such as treadmill walking and 6 minute walk test distance. Once at the start of stage 1 (month 1) and then at the start of stage 2 (month 7). Each optimization takes roughly 90 mins once per 6 months.