Cardiovascular Magnetic Resonance GUIDEd management of mild-moderate left ventricular systolic Heart Failure (CMR GUIDE HF): study protocol for a randomised controlled trial

Background Current heart failure guidelines recommend insertion of implantable cardiac defibrillators (ICD) for primary prevention of sudden cardiac death (SCD) in patients whose left ventricular ejection fraction is (LVEF) ≤ 35% on maximally tolerated medical therapy. However, the majority of sudden cardiac death (SCD) in patients with heart failure occurs in those with mild-moderate systolic heart failure (LVEF 36%-50%) who currently do not qualify for an ICD. At present, our tools to reliably risk stratify patients with mild-moderate heart failure to predict the likelihood of SCD are limited. Recent data however suggest that ventricular scar and/or replacement fibrosis, reliably identified on Cardiac Magnetic Resonance Imaging (CMR), forms a substrate for malignant arrhythmia, thus potentially identifying a group at increased risk of SCD. The primary aim of the Cardiovascular Magnetic Resonance GUIDEd management of mild-moderate left ventricular systolic Heart Failure (CMR GUIDE HF) trial is to test the hypothesis that among patients with mild-moderate heart failure, a routine CMR guided management strategy of implantable defibrillator (ICD) insertion is superior to a conservative strategy of standard care.