A Study of Triple-site Ventricular Pacing in Patients Who Have Not Responded to Conventional Dual Ventricular Site Cardiac Resynchronization Therapy

Inclusion Criteria: * Implanted with a CRT device \> 6 months previously according to current and conventional CRT indications * Device optimization \> 1 months previously * Aged 18yrs or older * Able to attend outpatient follow up Exclusion Criteria: * Recent MI (\<2 months) * Women who are pregnant or planning pregnancy * Severe co morbid illness (where patients are not expected to survive duration of follow up period or where repeated outpatient visits may not be in best interest of patients) * Upgrade procedure is contraindicated for safety reasons. * Class IV inotropic agents * Patient unwilling to comply with required follow-up protocol including randomization scheme