Role of Cardiac Computed Tomography in Optimising Response to Cardiac Resynchronisation Therapy

Inclusion Criteria: 1. Age \> 18, \<90 2. Patients with moderate or severe heart failure ( NYHA functional class II-IV) due to ischaemic or non-ischaemic cardiomyopathy. 3. QRS duration \>120ms on 12 lead ECG 4. LVEF \< 35% 5. LVEDD \>55 mm 6. Patients on optimum medical treatment for heart failure. The doses of these medications have been stable for 3 months. Exclusion Criteria: 1. Patients with a cardiac or cerebral ischemic event within the previous three months prior to recruitment 2. Patients who had had an atrial arrhythmia within one month prior to recruitment 3. Patients with a systolic blood pressure of more than 170 or less than 80 mm Hg 4. Patients with a heart rate of more than 140 beats per minute 5. Patients with severe renal failure (eGFR \< 30) 6. Patients with a history of allergy to iodine based contrast agents 7. Predicted life expectancy \< 1 year 8. Pregnancy