The purpose of the study is to determine whether MRI guided CRT implantation (using Siemen's software prototype) is superior to standard treatment in terms of CRT response. Data will be collected at enrolment, implant, pre-discharge, 6 weeks and 6 months. The total duration of the investigation will be 6 months.

The primary endpoint will be assessed by calculating the difference in the proportion of responders (>15% reduction in end systolic volume derived from 2-dimensional transthoracic echocardiogram at 6 months post CRT implant).

Inclusion Criteria:

• >18yrs of age
• Standard indication for CRT-P or CRT-D according to European Society of Cardiology (ESC)/European Heart Rhythm (EHRA) guidelines.1
• Stable on optimal medical therapy for at least 3 months
• Ischaemic aetiology
• Patients with atrial fibrillation can be included

Exclusion Criteria:

• Any contraindication to pacing /implantable cardioverter-defibrillator (ICD) implant
• Requirement for endocardial pacing
• Contraindication to gadolinium contrast enhanced cardiac Magnetic Resonance (MR) scanning
• Significant claustrophobia
• Significant renal impairment with estimated glomerular filtration rate (eGFR) <30 mL/min/1.73m2
• Existing pacemaker or ICD system or extraction of a CRT system within the last 6 months
• Participation in other studies with active treatment/ investigational arm
• Pregnant or planning to become pregnant in the next 7 months