Predicting Response to CRT Using Body Surface ECG Mapping

Inclusion Criteria: * Age \>18 years old * Fulfils established clinical criteria for CRT implantation (with or without a defibrillator) * NYHA Class III-IV Heart Failure (or NYHA II with NYHA III/IV symptoms in the preceding 12 months) * LVEF \<35% (Calculated using echocardiography or Cardiac MR) at the time of implantation * QRS duration \> 130ms * Optimal Tolerated Medical Therapy for Heart Failure Exclusion Criteria: * Severe, life threatening non cardiac disease * Active malignant disease and recent (\<5 years) malignant disease * Prior Heart Transplant * Recent history of unstable angina, acute coronary syndrome or myocardial infarction within three months of enrolment into the study * Pregnancy * Failure to participate in consent process * Atrial Fibrillation * Conventional pacemaker in situ * Heart Failure requiring constant intravenous therapy including diuretics and/or inotropes * Recent revascularisation procedure i.e. coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI) within the last three months